Flame Spectrometry J. D. Winefordner,‘ Department of Chemistry, University of Florida, Gainesville, Fla. T. 1. VickersI2Department of Chemistry, Florida State University, Tallahassee, Fla.
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PREVIOUS REVIEWS, fundamental developments in flame spectrometry have been included in the section on emission spectrometry (SOA). The large number of recent publications on flame spectroscopy has made it desirable to present a separate review of emission, atomic absorption, and atomic fluorescence flame spectrometry. Papers published in 1968 and 1969, those which appeared too late to be included in the previous review, and those needed to facilitate continuity of certain material are covered. This review is divided into five sections: Reviews, Books, and Bibliographies; Fundamental Studies; Atomic and Molecular Emission Spectrometry; Atomic Absorption Spectrometry; and Atomic Fluorescence Spectrometry. The majority of this review is devoted to material of basic importance to the field. Relatively few citations are reported for publications dealing strictly with applications of flame techniques. The review has been weighted heavily toward the Fundamental Studies and Atomic Fluorescence Spectrometry sections because of the lack of similar sections in the previous review (SOA) for both sections and because of the novelty of the latter section. Finally, some articles are considered in more than one section if the material is concerned with several areas of this review.
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REVIEWS, BOOKS, AND BIBLIOGRAPHIES
The first volume (11-4) of a projected three-volume series on flame spectrometry has appeared. This volume is devoted to theoretical aspects of the three flame spectrometric techniques and contains 13 chapters by a total of 16 authors. I n addition to an introductory chapter on the historical development and fundamental principles of flame spectrometry, there are chapters on several aspects of flame phenomena, atomization and excitation, temperature measurements and calculation, interferences, and accuracy and prec i sion. The book by Slavin (52A) is chiefly devoted to applications (with an element-by-element presentation of pertinent information), a short section on theory, and a somewhat longer section on instrumentation. The book by Work supported by AFOSR (SRC)OAR, V.S.4.F. Grant No. AF-AFOSR-
m-ixm. Work supported by PHS Research Grant S o . 5ROl GM 15996-02. 206R
Ramirez-Munoz (444) has a somewhat shorter presentation on applications and very extensive sections on instrumentation, range and limitations, and experimental methods. Both books contain a short description of atomic fluorescence flame spectrometry. These books are quite similar to two other books (15A, 47A). The excellent book by L’vov (d9A) on atomic absorption spectroscopy has not yet been translated into English. The atomic absorption spectroscopy book by Rubeska and Moldan (49A) has been translated into English. These authors have discussed atomic absorption theory, instrumentation, methodolgy, and applications and the “state of the art’’ of atomic fluorescence spectrometry so well that i t could serve as an introductory textbook for teaching the principles of atomic absorption spectrometry. Papers presented at the Atomic Absorption Spectroscopy Symposium a t the 1968 meeting of the ASThl have been published in book form @A). A revised edition of the Perkin-Elmer atomic absorption manual has been issued (%A). Evans Electroselenium, Ltd., has also issued an atomic absorption users manual (IYA), which like the Perkin-Elmer manual is loose-leaf and will be added to as additional methods become available. The finest atomic absorption spectroscopy conference ever assembled was held this past summer (July 14-18, 1969) a t Sheffield, England. A total of 56 outstanding contributed papers were given by authorities in the field of flame spectrometry. I n addition, eight plenary lectures were given by leaders in the field. These lectures, which will shortly be in book-form were: the applications of new techniques to simultaneous multi-element analysis by A. Walsh (He also received the fifth Talanta hfedal Award for his contribution to the evolution of atomic absorption spectroscopy; the award was presented to Dr. R a l s h a t the meeting.); progress in atomic absorption employing flame and graphite cuvette technique by B. V. L’vov; nonflame cells in atomic fluorescence spectroscopy by J. D . Winefordner; anion effects in atomic absorption and flame photometry by E. Pungor; a theoretical discussion of some aspects of atomic fluorescence by C. T h . J. Alkemade; developments in atomic absorption and atomic fluorescence spectroscopy by T. S. West; a critical evaluation of the analytical capabilities of flame atomic emission and absorption
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
spectroscopy by V. A. Fassel; and the behavior of certain elements in the absorption tube by B. Moldan. It is indeed unfortunate that the excellent, provocative, and critical talk by V. A. Fassel will not appear in print. A number of excellent reviews on various aspects of flame spectrometry have appeared since the review by hfargoshes and Scribner (SOA). Fortunately, the number of reviews in atomic absorption spectroscopy and even on atomic fluorescence spectroscopy have been far fewer than the number of research articles in the respective areas. I n the early years for both methods, the above statement was probably not valid. Perhaps the most distinguishing aspect of several of the reviews during the past two years was in regard to the rather critical comparison of flame emission with atomic absorption and atomic fluorescence. Several of these will be mentioned in some detail while others will only be listed. The popularity of flame emission spectrometry has greatly increased in recent years largely because of the experimental studies and resulting talks and papers by Koirtyohann and Pickett at the University of Xissouri and Fassel and his group a t Iowa State University. I n addition, the talks and papers on the fundamental aspects of flame spectrometry by Xlkemade and his group a t Utrecht and to some extent by Winefordner and his group a t the Cniversity of Florida have also helped in showing that flame spectrometric techniques are really quite similar and that there is little basis to the belief by many that atomic absorption spectrometry is superior to other flame methods. The complementary nature of atomic emission and absorption flame spectrometry was convincingly put forth in a review by Pickett and Koirtyohann (SYA). They compared the two techniques by using equivalent systems as far as possible, it., monochromators, flame type, and burnera. For elements having resonance lines a t wavelengths greater than 300 nm, flame emission generally produced lower limits of detection than atomic absorption spectrometry, whereas the opposite was true for those elements with resonance lines below 300 nm. Interferences, other than spectral, are similar for both techniques as are the instrumental requirements. Pickett and Koirtyohann also stressed that interferences can be significantly reduced and powers of detection
increased by appropriate selection of flames and conditions to the extent that flame methods are frequently preferable to other instrumental methods for the analysis of Zn, Cd, alkali and alkaline earth elements, and possibly for Al, In, Cr, hln, Pb, and the heavier rare earths. Zeegers, Smith, and Winefordner (62A) compared the shapes of analytical curves in atomic emission, atomic absorption, and atomic fluorescence flame spectrometry using derived expressions relating line radiances to the atomic concentration of vapor in thermal equilibrium. The influence of ionization, solute vaporization, compound formation, nebulizer yield, transport rate, and diffusion of atoms upon the shape of the analytical curves was discussed. Alkemade’s ( 1 A ) paper on facts and fantasies in atomic absorption flame spectrometry clearly demonstrated from theoretical considerations that atomic absorption is not superior to flame emission simply because the latter depends on the much smaller excited state population. H e showed that the so-called interelement interferences due to preferential excitation and quenching were much less likely to occur than has been suggested by numerous investigators. H e also demonstrated conclusively that resonance broadening has little influence upon the shape of analytical curves for analyte concentrations below about 1M. Finally, he showed that the shapes of analytical curves for atomic absorption flame spectrometry with continuum sources and atomic emission flame spectrometry should be similar. Other useful but more conventional reviews include the following. DeGalan (IbA) gave a general view of flame spectrometry. Pungor (42A) discussed developments in flame emission spectrometry from 1964 to 1966. Koirtyohann (%A) described the most significant developments from 1966 to 1967 in all types of flame spectrometry. Atomic absorption spectrometry was also reviewed b y malsh (55A), Rains ( 4 3 A ) , Kahn ( d S A ) , R e s t (69A) Lewis (27A), Price (%A) Piccolo and O’Connor (36A), Robinson ( 4 8 A ) ,Slavin and Slavin (5SA) , P\lassmanu ( 3 4 A ) , Brandenberger ( S A ) , and Ringhardtz and Welz ( 4 6 A ) . Flame emission spectrometry has been reviewed by Herrmann (22A) and Kirkbright ( 2 4 A ) . Grant (20A) has compared atomic absorption with other spectrochemical methods. Lewis (28A) and Warn (66-588) compared atomic absorption spectrometry with other instrumental methods. Erdey (16A) has considered the application of atomic spectroscopic methods in a general analytical laboratory. Vallee (54A) has conqidered applications of flame emission and atomic absorption for biological problems. Brech (9A) com-
pared optical emission and atomic absorption spectrometry for analysis of plant tissues. Beamish, Lewis, and VanLoon ( 6 A ) compared the use of atomic absorption and X-ray fluorescence for the determination of noble metals. Boettner and Grunder ( 7 A ) discussed the use of flame emission and atomic absorption for water analysis. The relative merits of atomic absorption and atomic fluorescence were compared by Winefordner (60A). Winefordner and Mansfield (61A ) reviewed the fundamental principles and previous work on atomic fluorescence flame spectrometry. Price (39A) reviewed the theory, principles, instrumentation, and uses of atomic fluorescence spectrometry. Demers (13A) and Ellis and Demers (14A) discussed the potential uses of atomic fluorescence spectrometry. A book dealing with atomic absorption spectrometry in geology was written by Angino and Billings (SA). Dawson and Heaton (10A) published a book on spectrochemical analysis of clinical materials which includes a discussion of flame techniques. Other books containing sections on flame spectrometry were “Proceedings of the XI11 Colloquium Spectroscopicurn Internationale’, (Ottawa) ( @ A ) , “Proceedings of the X I V Colloquium Spectroscopicum Internationale” (Debrecen) (41A ) , Volumes 6 and 7 of the “Developments in Applied Spectroscopy” series (4A, 2 1 A ) , and “Trace Inorganics in Water” (5A) in the Advances in Chemistry Series. Flame spectrometric methods were also included in books on methods of analysis of marine samples (32A) and fresh waters (19A). Marr (31A) wrote an interesting book on the spectroscopy of plasmas. Several bibliographies on atomic absorption spectroscopy have been maintained or initiated. The extensive bibliography of papers and talks by S. Slavin (60A) and W. Slavin (51.4) continues to be listed in Perkin-Elmer’s Atomic Absorption Newsletter. JarrellAsh (18 A ) and Bausch and Lonib ( H A ) have also made available bibliographies on atomic absorption spectroscopy. Aztec (45A)has maintained a fairly complete bibliography of atomic fluorescence spectrometry. Finally, LIasek and Sutherland (33A) are editors of a new document (initiated January-February, 1969) entitled “Atomic Absorption and Flame Emission Abstracts.” Abstracts are listed every other month for the world’s major periodical literature, conference proceedings, and a few unpublished reports. FUNDAMENTAL STUDIES
Flame Temperatures. T h e most popular method of measuring flame temperatures continues to be the line
reversal method. Thomas (134B) reviewed the general emission and absorption properties of radiation in the neighborhood of a spectral line. Doppler and collisional broadening processes were considered and appropriate line shape functions were derived. A relationship was derived for the intensity of an emitted line from a hot gas in thermal equilibrium. H e considered the influence of solid particles, such as soot, ash, unburnt fuel, and the cool boundary layer around the hot gases upon the intensity of radiation. IJsing the above fundamental approach, he derived the conditions under which spectral line reversal may be obtained. Thomas (135B) also described an automatic system for sodium line reversal temperature measurements. He discussed the systematic errors due to lack of thermal equilibrium between the sodium atoms and the flame gases, due to nonuniform flame conditions, due to incorrect positioning of the aperture stop, due to miscalibration of the reference source, and due to nonlinearity of the measurement system. Snelleman (129B) gave a clear and comprehensive description of the line reversal method. He discussed the errors associated with the reference light source, with the transmission properties of the lenses used in t h e setup, with reflection of emitted radiation from the hot gases by the optical system in the direction of the reference source, with restriction of the solid angle of radiation collected from the flame gases, with stray light emitted from parts of the flame not illuminated by the reference source, and with polarization of the transmitted light beam due to optical components within the spectrometer. Snelleman estimated the magnitude of the above systematic errors to be about 2 OK if care were taken to minimize such errors. Random errors were found to be primarily due to shot noise from the light source and to a lesser extent to Johnson-Nyquist noise of the anode resistor of the photodetector or haze of the photographic emission. By means of a rigorous procedure, he estimated that it was possible to measure a 0.5 O K difference in flame temperature using the line reversal method. The author also discussed the types of detection systems for line reversal measurements. To simplify the Abel inversion of a radial distribution of emitters in the flame, Krawec (85B) has described an electronic analog for performing the inversion to obtain temperature profiles. An advantage of this system was that the technique resulted in inversion “online.” Mustafin, Seleznev, and Shtyrkov (98B) used holography with a HeNe laser to measure the temperature distribution of a flame. Smith, Stafford, and Winefordner
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(128B) measured the temperatures using Ir/6O% 1r-40% R h thermocouples of a number of “wet” (water being aspirated) and “dry” low temperature H2-supported flames (air/H2, Ar/entrained air/He, X20/H2, and entrained air/H* flames) produced using total consumption nebulizer burners. Temperature contours and vertical height profiles for a number of flames were given. The principal source of oxidant in such flames was entrained air, and therefore the authors concluded that such flames have similar compositions. The similarity of quantum yields for a given atom in such flames was given as evidence for the latter conclusion. Willis et al. (142B) used the line reversal method to measure vertical temperature profiles of premixed, laminar K20/C2H2flames of different stoichiometries. The temperature of the region where most flame emission and absorption measurements were made was found to be 2880 OK (not the maximum temperature) which departed greatly from the widely quoted maximum value of 3228 “K. Kirkbright et al. (77B) used the line reversal method as well as the two-line method and obtained an average temperature of the red feather (interconal) zone of 3070 OK by the former method and 3025 OK by the latter method. The latter authors postulated that the CX radicals were essential to the promotion of dissociation of the metal monoxide species produced upon solute vaporization. Since such flames are in approximate thermal equilibrium, it is sufficient to say simply that the absence of 0-species within the red feather zone promotes dissociation of the metal monoxides. Willie, Fassel, and Fiorino (141B) measured the temperature of a P\TPO/H~ flame on a slot burner. They used the line reversal method to measure temperature profiles of stoichiometric and fuel-rich flames. Rapid temperature drops occurred above the primary reaction zone of these flames. The maximum temperature was about 2900 “K. The K;20/H2 flame resulted in a poor degree of freeatom formation and greater chemical interference than N20/C2H2 or 02/C2H2flames and was not recommended for analytical flame spectrometry. Dagnall, Thompson, and West (323)also studied the spectral characteristics of this flame and found the background to be five times lower than that of the air/CnH? flame. They recommended this flame for analytical flame spectrometry. Janin, Roux, and D’Incan (64B)measured the temperature of an 02/C2H2 flame burning in air or in N P by using the 1, 0 band of the rotation-vibration band of OH. The measured O H concentration in a N P sheathed 02/C2H2 flame agreed quite well with the calculated value indicating approximate 208R
thermal equilibrium. Chevaleyre et al., ( U B ) calculated the temperature of a methane/fluorine flame assuming thermal equilibrium. This value approximately agreed with the measured rotational temperature of the CN radicals. Flame Characteristics. Pungor and Halls (115B) studied the composition, structure, and emission spectra of various HB- and CzH2-supported laminar and turbulent flames (using 02,O2/N2 mixtures, N20, or C1F03 as oxidants) used in flame spectrometry. The influence of aspirated organic solvents on the above properties was also studied. The high degree of free atom formation of hydrocarbon flames was credited to the presence of C2, C H and CN radicals. Butler and Fulton (25B) measured the emission spectra, maximum flame temperatures, and burning velocities of C2H2 and propane (60%)/butane (40%) flames supported with X2Oor air. The iron particle tracer method was used to measure burning velocities, and the line reversal method was used to measure temperatures. During the past two years, Kirkbright, West, and coworkers have published a number of papers concerning separated flames (56B-58B, 78B-81 B ) . The separated flames were produced using either a quartz sleeve or an Ar- or NP- sheath gas. The resulting interconal zone no longer was plagued with the normal difficulties of air entrainment, secondary combustion, turbulence, and high background. The high excitation energy of the separated flame was useful in exciting some difficult to excite atoms. Dagnall, West, and coworkers (S4B,S5B, S7B, S8B) have also studied the molecular emission characteristics of S2, HPO, SnH, InC1, InBr, and In1 in cool NP/entrained air/Hz flames and in shielded air/Hn flames. Mossotti and Duggan (97B)described the construction and performance of a highly efficient total-consumptionburner that produced a low turbulence, fuel rich N20/C2H2flame from premised gases. The gases were premixed prior to introduction into the fuel and oxidant chambers of a total consumption burner. The premixed flame was spectrally similar but of much lower spectral radiance (more than 10-fold) than the corresponding unpremised turbulent flame. Homann (60B) studied the critical fuel/02 ratio for soot formation and the dependence upon temperature and pressure when using different hydrocarbon fuels. The shape and structure of the flame front for Bunsen flames has a great effect on soot formation. Vinckier and Van Tiggelen (1S9B) stabilized annular turbulent premixed 02/CHI and O2/C2H2flames by using an opposed jet burner. They determined the relationship between the turbulent and laminar burning velocities and the
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
intensity of turbulence. Sanematsu (122B) developed a theory to estimate turbulent flame burning velocities for a n air/CHd flame and obtained good agreement between measured and calculated values. Flames produced by using liquid fuel have recently been used by Bailey (8B) for spectrometric studies. An excellent bibliography on flames and combustion t’heories was written in 1967 by Anderson (SB). This article gave brief but well written sections on flame types (premixed and diffusion), flame geometry (flat, bunsen, and spherical), flame propagation, temperature profiles in flames, composition profiles, flame thermodynamics, and ionization processes in flames. Kinetic Band Equilibrium Processes in Flames. Gilmore, Bauer, and McGowan (48B) have written an extensive review summarizing the present knowledge concerning atomic and molecular mechanisms producing or removing rotationally, vibrationally, and electronically excited species in heated or excited gases. Rate coefficients for vibrational and electronic excitation and de-excitabion reactions were tabulated. Dixon-Lewis (41B ) derived time dependent heat conduction and diffusion equations for some simplified reaction mechanisms representing a fuel rich Nz/02/Hz flame. I n a second paper (42B),he derived equations for the diffusional, thermal diffusional, and thermal fluxes as well as for the mole fractions and temperature gradients in flowing reaction systems. Calculated values for these phenomena agreed quite well with corresponding esperimental values. I n a third paper (4SB) he measured temperature and composition profiles of a slow burning, flat N P / O I / H ~ flame at’ atmospheric pressure using a thermocouple probe and an optical method. Schlieren and shadow photography of the flame with the thermocouple probe indicated little disturbance within the flame gases due to the probe. Clarke (28B) studied the reaction broadening in an 0 2 , ” ~ diffusion flame and the influence of reaction broadening upon flame structure. Jesson and Gaydon ( Z B ) studied (for t,he first time) the absorption spectra of CH, CP, and CBfree radicals in the luminous mantle (feather region) surrounding the inner cone of a fuel rich O2/C2HZflame a t atmospheric pressure. By using a multiple reflection system, good spatial resolution was obtained. The presence of Cz and Cs radicals in luminous flames was considered with regard to soot formation. IlcEwan and Philips (91B) used the LiOH method to determine H radical concentration, the IO method to determine 0 radical concentration, and the XaOH method to determine OH concentration in fuel lean to stoichiometric hydrogen-nitrogen-osygen flames. A table of radical concen-
trations for the above flame type is given, Palmer (IO@) discussed the approach to the steady state in competitive consecut,ive gas reactions. Bulewicz ( d S B ) measured photometrically the intensities of CHI C2, and O H electronic bands in low pressure OZ/CZHZ, Oz/CH4, and Oz/butane flames as a function of pressure, stoichiometry, dilution, and nature of fuel. H e postulat’ed that the excited species of CH, CpJand OH were precursors to the chemi-ionization processes associated with such flames. Remy (119B) in a very extensive article described the types and structures of Oz/H2and O2/CH4 flames. He discussed methods of experimentally measuring the concentration of 0, H, OH, and other radicals and of measuring and calculating the extent of ionization of alkali metals and alkaline earth metals. H e discussed the formation of excited species of CaOH+, BaOH+, and SrOH+, the abnormally high concentrations of ions in hydrocarbon flames, and the recombination of positive ions with electrons or negative ions. The theoretical principles of atomic absorption and atomic fluorescence were also given. Schmitz (id@) presented a mat’hematical analysis of the stability of a one-dimensional model of a diffusion flame to small disturbances. Physical interpretations of the resulting criteria for stability were discussed. Parlange (106B) also treated the stability of a laminar flame subjected bo small disturbances. It was shown theoretically that preferential diffusion tended to stabilize the flame whenever the deficient species &-asalso the less mobile one. Halls and Pungor (52B) examined the relative radical and molecule concentrations in turbulent 02/Hz flames and found the O H and H radicals to be reH20 H. Verlated by Hz O H tical profiles of the H, OH, H2, and HzO species were measured by well known methods. The O H radical concentration in air/Hz flames reached a maximum high in the turbulent flame (about 7 cm) whereas the OH emission reached a maximum low in the flame (about 1 cm). The authors also considered the evaporation of droplets, flame gas expansion, and the blue continuum in such turbulent flames.. Crider (3SB)has noted chemiluminescence from some organic halides when introduced into air,”2 flames containing an SO2 background. Harrison and Juliano (53%) studied the influence of organic solvents on tin absorption in air,”? flames. The depressive effect of organic solvents on Sn absorption was believed due to the effective removal of H radicals which aid in the reduction of SnO to Sn or SnH. Absorption Coefficients, Intensities, Line Widths, Quantum Yields, and Collisional Cross-Sections. Hollander and Broida (59B) measured profiles of
+
*
+
atomic lines in flames by varying the wavelength of the emission line of an electrodeless discharge lamp operated a t microwave frequencies by means of a variable magnetic field. The absorption line was scanned (hO.01 nm) using the Zeeman a-components of a narrow emission line. Line profiles of a Zn line (307.59 nm) and two rotational lines of the 0, 0 and of the *2+-211 transitions in O H were measured. The damping constant, a, of the lines and the average collisional cross sections were derived from the profiles for N2/02/ClH~ flames having pressures from 50 to 760 Torr and temperatures from 2100 to 2300 O K . Other possible uses of this technique included measurement of line shifts and hyperfine structure and enhancement of sensitivity in atomic absorption studies. Yamada (143B) gave analytical expressions for the total radiance and equivalent widths of isolated spectral lines with combined Doppler and collisional broadened profiles. Jansson and Kolb (65B) have tabulated equivalent line widths of isolated lines with combined Doppler and collisional profiles for both weak and strong absorption and for the range of pure Doppler to nearly pure Lorentz line shapes. These authors compared their expressions with those of other workers. Information concerning the excitation-de-excitation processes of atoms in flames can be obtained by measurement of atom quantum yields. Jenkins (66B48B, ?OB) measured the fluorescence quantum yields and calculated the collisional cross section for deactivation of excited atoms of K a , K, R b , Cs, T1, and Li via collisions with HZ, H20, 0 2 , IT2, CO, C02, Ar and He. The experimental system for such measurements was described in detail. From a knowledge of flame gas composition and collisional cross-sections, it is possible to estimate fluorescence quantum yields which would be useful in explaining the shapes of analytical curves and the magnitude of the fluorescence signals in atomic fluorescence flame spectrometry. Hooymayers and Xienhuis (63B) measured fluorescence quantum yields of several alkali elements in a variety of flames. The experimental system and the calculation method to obtain the yields and cross-sections were described. Hooymayers and Lijnse (6dB) studied the influence of radiative nonequilibrium upon the occupation of excited states of metals in flames by measuring the deviation between the line reversal temperature and the true translational temperature as a function of metal concentration. The derivation should be of importance in low pressure flames and in flames containing large concentrations of inert gases, such as those used in analytical atomic fluorescence spectrometry. I t was also possible to determine
the quantum yield from the temperature deviation as long as the former was not too small. The fluorescence yields and quenching cross sections agreed quite well with those of Jenkins (66B). Pearce, De Galan, and Winefordner (109B)experimentally measured fluorescence power efficiencies of Mg, .4g, Cu, T1, Au, Pb, Ca, Rln, Co, Fe, and Cd in , fuel rich turbulent Oz/Hz, O Z / C ~ H Zand Ar/entrained air/Hz flames. The experimental system and calculation procedure were described in detail. The power efficiencies varied considerably from line to line (0.02 to about 0.3). However, as a result of considerable air entrainment, the values were quite similar for the same line of the same element in the three different flames. T h e authors also showed that atomic fluorescence produced during atomic absorption studies should seldom, if ever, affect the shape of the analytical curve. Several other studies on quenching cross sections included the ones by McGillis and Krause (92B) and Belliso, Davidovits, and Kindlmann ( I S B ) . Hooymayers (61B) derived an explicit expression for the intensity of atomic resonance fluorescence as a function of atomic concentrat’ion in a flame. The expression derived was valid for both pure Doppler broadening as well as combined Doppler-collisional broadening of the absorpt,ion line. The derived expressions were used t’o calculate log intensity us. log atomic concentration curves for a number of different damping constant values. The calculations were only applicable to a single isolated resonance line excited via either a very narrow line or a very broad (continuum) line. The author also indicated t’heprocedure to determine the a-parameter and the quantum yield from the asymptotic behavior of the analytical curve if the at,omic concentration a t the intersection of the low and high concentration asymptotes were known. Zeegers, Smith, and Winefordner (146B) using the Hooymayers’ approach derived simplified expressions for the line radiance for the low and high concentration asymptotes in atomic absorption, atomic emission and atomic fluorescence flame spectrometry. They also discussed other factors influencing the shapes of the experimental analytical curve3 in the three flame methods. Jenkins (69B)analyzed the factors det,ermining the intensity, the signal, and the signal-to-noise ratio in atomic fluorescence spectrometry. He particularly was concerned with the effect of the flame gas composition on the fluorescence yield. h table of pseudo-first order rate constants for the quenching of excited E a atoms was also given. Razumov and Fishman (118B) measured the absolute concentration of atoms using atomic absorption. They determined the absorpt’ion coefficients
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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for a given frequency by convolution of the Voigt profile. They were concerned particularly with the measurement of H g in air. Orren (103B) considered the basic principles of atomic absorption spectrometry, Le., the relative population of levels of atoms in thermal equilibrium, the relative degree of ionization of atoms in thermal equilibrium, the influence of broadening, and the intensity expressions. ,4lkemade (2B) also considered some of the factors influencing the shapes of atomic absorption analytical curves. Yasuda (144B)measured the linearity of atomic absorption analytical curves for Ag, Cu, Sr, and Ca using a FabryPerot interferometer. These results were compared with theoretically predicted curves; by assuming the temperature of the hollow cathode sources was between 1200 and 1300 OK, self-absorption was between 0% and 22yo,and the emission line was symmetrical and unshifted in position, he found the resonance absorption line to be 1.5 to 2 times broader than the source resonance line. The absorption line was found to be shifted in wavelength and unsymmetrical. Rann (116B) has performed a n extensive study of the use of a flame as a spectral source for atomic absorption spectrometry. A theoretical treatment of atomic absorption was developed with the use of the Voigt profile equation. I n his treatment, the flame source resulted in approximately half the analytical sensitivity obtained with a narrow line hollow cathode source. Rann (1 17 B ) also considered the possibility of absolute atomic absorption analysis. For such studies, a precision burner producing a homogeneous flame was described. Using this burner, he obtained excellent agreement (within 50%) between experimental and predicted results. The main difficulties stemmed from the lack of accurate data on the free atom fraction, the extent of collisional broadening, and the characteristics of the emission line from the source, Boumans (183) calculated the intensities of 200 persistent atom and ion lines of 53 elements a t three different temperatures (5000, 5600, and 6200 O K ) for a dc arc plasma in air in thermal equilibrium. He considered excitation, ionization, aiid transport processes in the calculations. De Galan, Smith, and Rinefordner (39B) calculated electronic partition functions of the atoms and first ions of 73 elements over the temperature range of 1500 to 7000 OK. The results were presented in the form of a fifth order polynomial expression which has been fitted by a method of least squares. Boumans (17B) using these results determined numerical correction values to account for the temperature dependence
of the electronic partition function of atoms of 40 elements. He defined a temperature-dependent apparent excitation potential and a similar ionization potential and gave tables of such values for 58 elements over the range of 15007000 OK. Compound Formation and Ionization in Flames. Schofield (123B) has reviewed the literature concerning dissociation energies of the Group I I a diatomic oxides. Zeegers, Townsend, and Winefordner (147B) measured the free atom fractions of Ca, Sr, and Ba; these values agreed quite well with calculated values indicating the flame (air/CzHz) to be in thermal equilibrium. From the free atom fractions for Rfg, Cr, Fe, and Mn, dissociation energies of MgO, CrO, FeO, and A h 0 were estimated and found to agree quite well with previously measured values. Cotton and Jenkins (29B) used atomic absorption spectrometry to measure the concentration of alkaline earth atoms as a function of H radical concentration in fuel rich N2/02/H2 flames. I n these flames, the monohydroxide and dihydroxide as well as the monoxide were found to be significant. They measured the bond dissociation energies of the monohydroxides and dihydrosides. Cotton and Jenkins (SOB) by a similar method measured the bond dissociation energy of MgO. The method used had the advantage over previous methods of not requiring a calibrated aspirator or any values of spectroscopic parameters relating fractional absorption to metal concentration. The amount of hydroxide formation for M g was found to be negligible. Cotton and Jenkins (31B ) also measured the bond dissociation energies of gaseous alkali metal hydroxides (LiOH, NaOH, KOH, RbOH, and CsOH) using the same method. The thermodynamic stability (free energies of formation) of l f g o , &03, A10, A1202, A120, MgA1204, LZgC1, hlgCis, Lagos a t 2400 O K and BeO, MgO, CaO, SrO, B a 0 , h1203, La&, BeAA1204, hlgAl~O4,Cari1204, SrX1204, BaA1204and 4/3 LaA1O3 a t 2000 OK were tabulated by Mansell (93B). Manse11 concluded from the free energy values that since MgA1204 is the least stable of the alkaline earth aluminates, such elements as Sr, Ca, etc. should result in the release of Mg atoms in flames with the simultaneous effect of producing Sr-, Ca-, and other metal aluminates. Pleskach and Rykov (112B)studied the formation of phosphorus compounds with calcium. Golden (5OB) calculated the spectral absorption coefficients for several electronics transitions in some diatomic molecules. He tabulated oscillator strengths and spectroscopic constants for 50 transitions in 23 molecules. Jensen ( 7 l B ) studies electron attachment and compound formation in fuel rich ?;d02/H2 flames a t atmospheric
210R * ANALYTICAL CHEMISTRY, VOL. 42, NO. 5 , APRIL 1970
pressure. Addition of boron to these flames seeded with alkali metals resulted in reduction in the concentrations of free alkali metal atoms and in the formation of negative boron containing ions. Standard heats of formation for KBO2, E a B 0 2 , and LiB02 and the electron affinity of BO2 were measured. Hayhurst and Sugden (54B) studied the influence of halogens on the ionization of alkali-laden H2- and C2H2-type flames. The results showed that in the presence of halogen species, the alkali atom ionizes via electron exchange, whereas, without the halogen, the alkali ionizes via a collisional process with a third body. Bulewicz and Padley, (24B) introduced small proportions of electron acceptors, such as chlorine or bromine, into low pressure 02/C2H2 flames and obtained a marked reduction in the free electron concentration in the reaction zone. The measurements strongly suggested the process HX e- = H X-. Traces of cyanogen, sulfur, and ammonia also caused similar electron concentration reduction. From these studies, the electron affinities of C1 and Br were determined. Kelly and Padley ('74B)used a rotating single probe in studies of ionization of metal additives in premixed Pi2/02/H2 flames. They measured the positive ion concentrations of Ga, In, and T1 and estimated the rates of ionization and recombination over the range 2200-2800 OK. The results are consistent with the process 11 X = M+ e X. Kelly and Padley (76B) also measured the positive ion concentrations of various transition metal salts introduced into the same flame listed above. Measurements were taken as a function of additive concentration, form of additive salt, flame temperature, and height in flame and indicated a more complex behavior than with the alkali and alkaline earth metals. When alkali and transition elements were sprayed into the flame, the ion concentration was greater than was expected asssuming the two salts had no mutual effect. Data seemed to indicate that solid particles promoted equilibrium ionization of alkali metals via a solid-state reaction. Zeegers, Townsend, and Winefordner (147B) measured free atom fractions, p, of Ca, E a , Sr, U g , Cr, Fe, and Mn. They used a relative atomic absorption method which gave p-values with systematic errors no greater than 10%. I n their method, the absorption of radiation from a continuum source was compared with that from copper, the reference element which had a of unity. Because a relative method was used, the results were not sensitive to wavelength dependence of the photodetector, and it was not necessary to measure accurately the spray efficiency of the nebulizer, the transport rate, losses of solution in inter-
+
+
+
+ +
connecting tubing, arid the spectral bandwidth of the monochromator. Koirtyohann and Pickett (8SB) measured 0-factors for Al, Ba, Ca, Cd, Co, Cr, Cu, In, Mg, Mn, Na, Sn, Sr, V, and Zn using line sources and both lean and fuel rich air/CzHz and NzO/CZHz flames. It is interesting to compare values for the air/CzHp and NzO/CZHZ flames. For a n element forming a stable monoxide in the flame, e.g., Al, 0 was much larger in the Nz0/C2Hzflame, Le., fi 7 in air/CzHz and p 0.3 in NzO/ CzH2; whereas for a n element forming weak monoxides, e.g., Co, 0 was about the same in both flames, Le., about 0.1. Elements forming stable molecular compounds in the flame have much larger values in the hotter NzO/CZHz flames. Cowley, Fassel, and Kniseley (SdB) have measured atomic and molecular absorption and emission spectra and the vertical profiles of various natural species of the flame (CN, CH, CS, and OH) and species formed upon nebulization of salts (La, Sc, V, Cr, ScO, and L a o ) into premixed Oz/CzHz flames. The data were interpreted in terms of: the relative concentrations of reactive intermediates and stable species in the four flame zones (preburning zone, reaction zone, interconal zone, outer mantle); the mechanism of free atom formation from aerosol droplets; and free atom depopulations processes. According to the authors, the great increase in atom population for many elements-particularly those forming stable molecular compounds with flame gas products-in the interconal zone of the fuel-rich 02/C2H2 flame was due to a deficiency of 0 atom concentration. Nebulization. Hieftje and Malmstadt (55B) recently described a unique system for producing droplets a t a given rate (0.1-200,000 droplets/second) and of a precise and accurate (10-200 p ) size. The time and spatial control permitted introduction of suitable measurement equipment for observation of the evaporating individual droplets and vaporizing individual salt particles. The authors used the generator to study solvent evaporation of water, 100 ppm sodium chloride in water, ethanol, methanol, and acetone, and CCl, and to measure evaporation rate constants. The authors also indicated the possible use of the generator to study dropletparticle interactions, droplet-vapor interactions and vapor-vapor interactions. Stupar and Dawson (1SSB) discussed the most common theories of producing aerosols, including pneumatic and ultrasonic nebulization. The experimental results indicated that ultrasonic nebulization must be operated a t high frequencies (above 500 KHz) and high power to obtain fine aerosols (about 5 p) a t sample flow rates of 1-5 ml/min if ultrasonic nebulization was to improve
-
upon pneumatic nebulization. Spitz and Uny (1SOB) discussed ultrasonic nebulization. The gain in sensitivity in atomic absorption spectrometry due to the use of an ultrasonic nebulizer rather than a pneumatic nebulizer was about 10-20 times because of the amount and fineness of the aerosol introduced into the flame. They studied the influence of frequency, power applied, geometry of the nebulizing chamber, and gas flow and utilized these results to develop an ultrasonic nebulizer for routine analyses. Limits of Detection. I n this section, only papers dealing with the definitions and measurement of limits of detection, noise, and signal-tonoise ratio will be listed. St. John, McCarthy and Winefordner (121B)used a statistical method to define the limit of detection as that concentration resulting in a signal-to-noise ratio of the “Student” t times & divided by the square root of the number of measurements of sample and blank. When one assumes the sample and blank were measured for a sufficient time period t o account for most noises and drift, then the signal-to-noise ratio a t the detection limit was taken as 2. Barney (IbB) defined sensitivity as the slope of the analytical curve, and limiting sensitivity as the slope in the region of the limit of detection. The limit of detection (called detectability) was defined as the limiting detectable increment of analyte and was the ratio of the standard deviation of the output signal (rms noise) a t the detection limit divided by the limiting sensitivity. Therefore, he indicated that all authors reporting detection limits should also report the limiting sensitivity and the standard deviation of a single measurement. Parsons (107B) defined the limit of determination as the lowest concentration determinable with a desired relative standard deviation. The limit of detection and limit of determination were simply related. Belyaev, Ivantsov, and Karayakin (14B, 15B) measured the frequency spectra of phototube shot noise and optical fluctuations of the most widely used light sources in spectrometry over the frequency range of 20-10,000 Hz (sources studied were: dc arc; ac arc; plasma jet; electrodeless discharge lamp; hollow cathodelamp; incandescent lamp ; 0 2 / H z flame; and air/CzHz flame). Low frequency fluctuation predominated in all frequency spectra and exceeded the shot noise as long as the light flux from the source exceeded about) lumen; the high frequency electrodeless discharge lamps and hollow cathode lamps were exceptions to this because the source noise was indistinguishable from the shot noise of the phototube.
Prugger (114B) recently described the noise sources in atomic absorption spectrometry. I n this paper, he also gave spectral radiances of some light sources and the noise frequency spectra between 20 and 600 Hz for several elements (and the corresponding blanks) measured by atomic absorption spectrometry. Lebedev and Dolidze (89B) also described the low frequency noises (0.5-5000 Ha) of various flames. The turbulent flames produced from O2/H2 and OZ/CzHz had the greatest noise. The optical noise in a flame was due to convection of gases and turbulence. Parsons and Winefordner (108B) gave a brief description of the critical instrumental parameters t o be optimized for atomic absorption, atomic emission, and atomic fluorescence flame spectrometry. Several optimization techniques were discussed in the paper. Shatkay (126B) discussed in detail the methods (working curve method, simulation method, standard addition method, successive dilution method, and changing parameter method) for photometric determination of substances. The methods of standard addition or of successive dilution allowed the determination of an analyte in the presence of strongly interfering substances even when the working curve method failed. The changing parameter method allowed the determination of a substance despite the interferenf with an accuracy limited only by the precision of the measuring device. Instrumentation. I n this section, a number of articles which are not necessarily concerned with flame spectrometry but which may be of future interest to workers using flame spectrometry will be mentioned. Articles dealing specifically with instrumentation in flame spectrometry will be mentioned in the appropriate sections. Sources of Radiation. Lowe (90B) described a technique whereby the resonance lines were selectively modulated inside a standard hollow cathode lamp without using extra modulation electrodes. This was done by operating the hollow cathode a t a steady dc level and superimposing upon this a series of short high-current pulses. By adjusting the pulse height, the vapor cloud characteristic of the cathode metal was modulated producing alternate 100% transmission and nearly 0% transmission. This system used in an atomic absorption instrument could also have been used in atomic fluorescence studies. Gofmeister and Kagan (49B) studied the electrical and optical characteristics of hollow cathode discharge in neon. The influence of different size cathode, argon pressure, and current densities upon the radial and axial distribution of electron concentration and intensity was studied. The results indicated thermal
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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equilibrium of a number of excitation levels. Semenova, Gorbunova, Bokova, and Sukhanova (125B) experimentally studied the mechanism of the hollow cathode discharge. The volt-ampere characteristics of C, Fe, and Ca vapors produced using a pure carbon cathode were studied. The discharge temperature, the positive ion concentration, and Doppler half-widths of spectral lines were measured. The vapor temperature and ion concentration was critically dependent upon the discharge voltage. Tkachenko and Tyutyunnik (1S6B) studied the influence of a magnetic field upon the discharge in a hollow cathode. The applied magnetic field resulted in decreases in the electron temperature at the cathode center, the particle mobility, and the intensity of atomic lines and molecular bands. Bodretsova et al. (16B)measured the electrical properties, the emission line widths, and the intensities of hollow cathodes made from various metals and filled with various inert gases (He, Ne, Ar, or Xe); these parameters w r e measured as a function of inert gas pressure and type and current density. Katskov, Lebedev, and L'vov ('i'3B) measured the spectral characteristics of pulsating hollow cathode lamps used for atomic absorption studies. Emission intensities, line widths, and line contours were measured a t different dc and pulsating current levels. At the same average current, the line widths were slightly greater and the intensity much greater (20-130 times) when using pulsating current. Other advantages of pulsating currents included simpler lamp construction, absence of variation of intensity on heating, lesser dependence of intensity on gas pressure, and longer lifetimes. Bueger and Fink (19B) measured line intensities in the negative glow zone of hollow cathodes and noted a fall in intensity for all lines near the edge of the glow zone. Calculated excitation temperatures also decreased toward the glow edge. Bueger et al. @OB, 21B) investigated the use of hollow cathodes in analysis. Bueger and Fink (20B) evaporated solutions within the metal cathode and operated with Ar at a pressure of 3 Torr and with a current of 400 mA. Emission intensities stabilized within 3 min. Analysis of impurities within the evaporated solution required 15 min. Bueger, Maierhofer, and Reis (21B) quantitatively analyzed gas mixtures in a hollow cathode at a high current. The intensity of the measured lines was critically dependent upon the electron temperature and concentration of excited atoms. The excitation of a gas mixture favored the gas components with lowest ionization potential. Nitrogen gas adsorption to the cathode required special clean-up procedures between analyses. Bueger and Scheuerman (22B) measured excitation temper212 R
atures in a high current hollow cathode. The negative glow of the hollow cathode consisted of a nonthermal plasma, and so the Saha and Corona ionization equations were not applicable. Equations were derived to estimate relative intensity as a function of excitation temperature which increased as pressure and cathode bore size decreased. A mechanism of excitation and ionization in a hollow cathode was postulated. A comparison was made between the spectral lines emitted within the cathode layer to those in the negative glow region. Tsukamoto (137B) investigated the spectroscopic characteristics of five cathodes of Ag and Cu for various currents, gas pressures, and cathode compositions. Curves of sustaining voltage and spectral intensity as a function of discharge current and cathode composition were given. The voltage and intensity increased with increased current, Prugger (11SB) gave spectral plots of the measured spectral radiance of a number of continuum light sources. Radiances of a number of line sources, including hollow cathode and electrodeless discharge lamps were also given. Grimm (51B) described in detail the construction and use of a low pressure discharge lamp which could be operated either as a glow discharge lamp or a hollow cathode lamp for spectrochemical analysis. Current-voltage curves at different gas pressures were given. Mansfield et al. (94B) described the construction and operation of electrodeless discharge lamps for 14 elements. By using a statistical evaluation of data, it was shown that source intensities useful for atomic fluorescence were directly related to the lamp diameter, gas fill pressure, and form of metal but were independent of weight of metal introduced into the lamp. The optimum tube diameter, gas fill pressure, and form of metal for producing analytically useful atomic fluorescence were listed. Problems encountered in the construction of useful sources were given. Also a comparison of microwave (2450 MHz) antenna and cavity coupling devices were given. The A-antenna with quartz insulation around each source was recommended for atomic fluorescence studies. Later, Zacha, Bratzel, Winefordner, and Mansfield (145B) recommended an evacuated quartz jacket around some lamps t o thermally insulate the lamps from ambient temperature fluctuations. Silvester and McCarthy (127B) studied the experimental parameters (choice and pressure of inert gas, amount of metal, and microwave power) affecting the intensity of a Cd-electrodeless discharge lamp. By means of a statistical design, they optimized the Cd tube for operation a t 2450 MHz and 200 watts. Baranov, Mashtakov, and Pofralidi (10B) tabulated the working
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5 , APRIL 1970
parameters of high frequency electrodeless discharge lamps for 15 elements. The maximum ignition current, working current, radiation intensity, line halfwidths, and lifetimes were given for each lamp type. Modulation properties of the lamps were investigated. Pechorin and L'vov (11OB) developed high frequency electrodeless discharge lamps for elements difficult to vaporize, e.g., IlloCla, FeC12, and M n C L The emission intensity of the lamps was 100-1000 times greater than the corresponding hollow cathode lamps. The Mo and F e lamps were used for more than 100 hours with no loss of intensity. The M n lamps decreased in intensity with operation, probably because of the reaction of MnClz with CaO from the quartz envelope. Klein (82B) measured the spectral radiance of a high pressure xenon arc lamp in the stationary (2.2 KW) and pulsed (10 KW) modes in the spectral range of 300 nm to 2p. Excellent stability and reproducibility resulted in either mode of operation. An expression was given relating the spectral radiance to the temperature and pressure of the arc. The temperature profile of the xenon arc was obtained by using the derived expression and b y applying the Planck-Kirchhoff method to the Abel inverted emission and absorption of a n IR line. Photodetectors. O'Haver and Winefordner (100B) have derived a n equation for the anodic shot noise of a multiplier phototube by considering the thermionic emission from the dynodes as well as the cathode. The shot noise was about 10% greater if thermionic emission from the dynodes were considered than if it were neglected. T h e calculated shot noise equation gave good agreement with experiment. Cetorelli a n d Winefordner (26B) used signal-to-noise ratio expressions and measurements to evaluate the photoanodic sensitivity factor and the effective gain of a 1P28 multiplier phototube. Mayden and Shaanan (95B) found a logarithmic relationship between the voltage and gain of a group of three dynodes. Barna and Cisneros (11B) conducted high speed light pulse studies on the Amperex XP-1210, 10 stage multiplier phototube a t a voltage of 4.5 kV and gain of 2 x 107. The light pulser was a gallium phosphide diode pulsed by two 0.8-nsec wide pulses at various intervals. Lavoie and Winston (88B)described an active magnetic shielding system for multiplier phototubes. Fields as great as 100 G were effectively shielded. Kennedy, DeLorenzo, and Brashear (76B) designed a versatile voltage sensitive preamplifier for use with multiplier phototubes. The unity gain rise time was 5 nsec. Larkins et al. (87B) described the use
of solar-blind multiplier phototubes for flame spectrometry. Such devices have virtually zero response a t wavelengths greater than about 310 nm and should have great use for resonance detectors and especially for atomic fluorescence studies. Spectrometric Systems. D e Galan and Winefordner (4OB) have given solutions of the convolution integral for triangular, Gaussian, and Lorentzian slit functions folded on Gaussian and Lorentzian shaped emission and absorption lines. Expressions for the irradiance and radiant flux were given for the different combinations of line profiles and slit functions. Expressions in the limit of narrow arid wide slits were used to discuss: the measurement of the total intensity or total absorption of an atomic line, instrument calibration with a continuum source, definition of the spectral bandwidth, and the advantage of using a peak integrating device in the photoelectric detection of atomic spectra. Kruegle and Dolin (86B) described a rapid-scan spectrometer for scanning 200 nm to 15 p in 3 sec. The device was used to determine the absorption and emission spectra of hot gases. The measured resolution a t 312.5 rim was better than 0.6 nm and a t 3.3 p was better than 0.011 p. Other rapid scan spectrometers of possible interest to flame spectroscopists have been described by several research groups ( 9 B , 84B, 11 1 B , 120B, 132B). Stauffer and Sukai (131B) described the technique of derivative spectroscopy. This method is an effective means of enhancing detectability of overlapped spectral bands, suppressing of background radiation, and minimizing stray light and atmospheric turbulence problems. Williams and Kolitz (140B) described a method called molecular correlation spectrometry for determination of trace concentrations (ppb) of gases of importance in air pollution. By use of an oscillating mask a t the focal plane of the monochromator, the signal due to light absorption was maximized when the slits in the mask were made to exactly coincide with the absorption maxima of a certain molecular species. The ac signal was measured by a phase-sensitive-amplifier locked into the proper frequency and phase of the oscillating signal. The system was used to detect parts-per-billion of certain gases in the presence of other gases with a precision of better than f10%. Artem’ev et al. (4B-YB) has described the construction and use of a fast correlation photon counter for visible spectra. The device was used to measure the time correlation of photons in coherent light fluxes by using a spiral delay line which caused standing waves to be produced. The transient response of multiplier phototubes, the width and
shape of the 587.1-nm Kr line from a discharge tube, and the lifetime of photons emitted by a Kr-gas laser and a He-Ne laser in several modes were studied. Because the time resolution was less than 1 nsec and the sensitivity was greater than watt, it would seem that this device would have some use in applied and fundamental studies in flame spectrometry. Nicol (99B) described the construction and operation of a doublebeam spectrophotometer for the direct measurement of integrated absorption lines. Foskett and Weinberg (45%) have analyzed the Michelson spectral line discriminator as a linear device. The instrument was capable of measuring spectral discontinuities in the presence of strong background continua. The appropriate equations for several analytic line shapes were presented. Photon Detection Systems. A number of articles concerning photon counting have appeared in the past two years. Foord et al. (45B) assessed number of multiplier phototubes for photon counting. They concluded that the ideal multiplier phototube would have a small cathode (low dark count) and would produce narrow pulses (useful for high count rates). For statistical experiments, there should be no correlations either of the dark counts or the signal counts. Tu11 (138B) compared photon counting and current measuring systems for use in spectrometry of low intensity light sources. The dark noise component due tocerenkov pulses in multiplier phototubes (pulses produced by cosmic ray mu mesons) was shown to be the limiting factor in dc measuring systems. Photon statistics and the signal-to-noise ratios for both photon counting and dc charge integration devices were given, and the advantages of photon counting over the dc method were listed. Morton (96B) condidered the criteria for selecting suitable multiplier phototubes and methods of calculating the counting errors that may occur during measurement. The use of photon counting with simple photoconductive devices was shown to be poor unless carrier multiplication with photoconductive multipliers was used; such devices with high quantum efficiencies and wide spectral response should ultimately replace multiplier phototubes for photon counting. Franklin, Horlick, and Rilalmstadt (47B) studied the basic and practical considerations for using photon counting in quantitative spectrometric methods. The advantages of photon counting over other methods were listed as: direct digital processing of discrete spectral information, decrease of effective dark current by several orders of magnitude by discrimination, increase in signal-to-noise ratio, sensitivity to
low light levels, accurate signal integration, improved precision of analytical results, elimination of reading error, and better spectral resolution. To demonstrate the use of photon counting in spectrometry, photon counting was used for standard absorption spectrophotometry. Eather and Reasoner (44B) gave design details for constructing an optimized tilting-filter photometer for detecting weak light signals. The photometer electronics system was simple and inexpensive and was linear up to 10 MHz counting rates. Alfano ( 1 B ) described a technique to reduce unwanted scattered light and ghosts in Raman spectroscopy. I n this method, the Raman spectra were chopped and phase detected while the Raleigh scattering and unwanted ghosts were not. Pao and Griffiths (105B) have described a clever device for detecting low light levels. I n this method, the conventional slowly varying signal was discarded, and the mean of the square of the fluctuations was detected instead. I n principle, the incident light could be detected equally well by this method. However, this system was very effective in discriminating against dark noise and in practice performed better than either dc or phase-sensitive systems a t low light levels. O’Haver and Winefordner (101B) described the construction of a simple, inexpensive, versatile, solid-state, constant band-width recording nanoammeter for measurement of phototube currents (10-5-10-~~ amp full-scale). O’Haver and Winefordner (102B) also described a solid-state source intensity compensating device for use in atomic fluorescence spectrometry. The method used was similar to the use of an internal standard used in many directreading emission spectrometers and was based on the analog integration of the fluorescence and source monitor signals (one phototubedetected the fluorescence and one detected directly the excitation source). When the source monitor phototube-amplifier-integrator circuit recorded a set “intensity” level, a relay terminated the integration of the fluorescence signal resulting from a phototube-amplifier-integrator circuit. ATOMIC AND MOLECULAR EMISSION SPECTROMETRY
Instrumentation. Flames and burners, nonflames, optical systems, detectors, measurement systems, and specialized instruments will be reviewed. Several articles reviewed in the Fundamental Papers section are mentioned again in this section b u t with regard to analytical studies rather t h a n more fundamental studies. Flames and Burners. Nitrous ox-
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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ide supported flames continued to be a subject of considerable interest. Pickett and Koirtyohann (7SC, 97C, 98C) described the use of the N20/ C2Hzflame for emission analysis. They used a conventional slot burner with the long axis aligned with the optical axis and found a large increase of intensity (and only a slight increase in selfabsorpt'ion) compared to arrangements with a shorter path. They reported detection limits for a large number of elements wit'h this system. Christian (17C) has also investigated the use of the K20/CzHz flame on a slot-type burner for emission analysis. He observed the emission of 52 elements and reported detection limits. For a number of elements his detection limits were 10 to 100 times poorer than those of Pickett and Koirtyohann (72C, 97C, 98C). The discrepancy was unexplained. Fiorino, Kniseley, and Fassel (S7C) described the construction and operation of a particularly versatile burner. The burner was of the slot type and could be operated with premixed 02/C2H2 as well as N20/CzHz flames. An interesting and worthwhile feature of this paper was t'he discussion of the principles of burner design. Absorption spectra for flame species such as Cz and CN were reported, and atomic absorption detection limits of a number of elements were compared for t'he 02/ CzH2and N ~ O / C ~ Hflames. Z PIIossotti and Duggan (90C)described a system for producing a premixed N20/C2Hz flame with the cylindrical shape niore common to flame emission analysis. I n this system, NzO and C2H2were mixed a t each entry port of a conventional total consumption burner so that a N20/C2H2 mixture issued from both the fuel and oxidant ports of the burner. Detection limit's in terms of concentration were similar to those reported with the Kniseley burner but somewhat' poorer than those reported with the long slot burner (72C, 97C, 9%').
The possible analytical utility of the K 2 0 / H z flame was examined by Dagnall, Thompson, and West' (27C) and by Willis, Fassel, and Fiorino (140C). The two groups arrived a t rather different conclusions as to the usefulness of this flame. Dagnall el al. (27C) felt the flame showed considerable promise for emission and absorption. Willis et al. (l4OC) found that the r\'20/Hz flame had a temperature only 150" less than that of S20/C2H2flames, but for most elements, it yielded considerably poorer detect,ion limits than those found for NzO/C2H2flame. West et al. (51C, 64C, 65C) continued their studies of separated flames and have investigated the utility of a separated NzO/CzHzflame for emission analysis. X silica tube was used as the separator with the flame viewed through 214 R
a window attached to a side arm on the separator. They reported that this arrangement resulted in a large reduction in flame background emission and an enlargement of the fuel rich region. Reported detection limits were, for the most part, somewhat poorer than those reported with the slot burner premixed N20/C2H2 flame (SSC, 72C, 97c, 98C). West et al. ( Y C , 54C, 55C, 62C, SSC) also described investigations of air/CsHz and N20/C2Hz flames shielded by a stream of nitrogen or argon. Again the advantages were reduced flame background emission and an enlarged fuel-rich zone. Reduction of OH flame background emission is reported to be sufficient to allow determination of Bi at 306.8 nm. Kirkbright and West (66C) presented a survey of their work with separated flames. Chapman and Dale (1SC) described a burner modification which allowed 0, enrichment of a premixed air/C2Hz flame. The problem of adequate monitoring and reporting of the flow rate of gases for flame spectrometry was the subject of two brief communications (61C, 81 C). The introduction of sample to the flame received attention in several papers. The sensitivity enhancement attainable by use of heated air was briefly discussed (107C). A system was described (13'6C) for producing a dry aerosol from a solution. The system employed a pneumatic sprayer, a heated chamber, and a condenser for removal of solvent vapor. A very similar system which used an ultrasonic nebulizer was also described (S2C). Two complete burner systems with provision for solvent removal were described (47C, lS7C). Several recent papers (85C,123C, 125C, 126C, lS8C) described arrangements for convenient utilization of ultrasonic nebulizers. Additional work on intermittent sample nebulization was reported (112C, IS4C). Sample introduction was modulated a t 50 Hz by oscillation of the capillary submerged in the solution. Some modulation of the flame background emwion also occurred with aqueous solutions. An order of magnitude hiprovement in the detection limit for X g was reported (134C) with this technique. Hieftje and Malmstadt (49C) explored the utility of the isolated sample droplet method for analysis. They were able to demonstrate a long term relative standard deviation of 0.17, for measurements carried out with the system. They found absolute detection limits for Na and Ca of 6.9 X g and 2.7 X 10-14 g, respectively, and relative detection limits of 0.00002 ppm and 0.001 ppm, respectively. Several devices have been described which permit the direct analysis of
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
samples which are not in solution form. Woods (14SC) and Coudert and Vergnaud (18C) described devices for the direct introduction of powders into a flame, and Crider (SOC, 2SC) and Pueschel (IOSC) described devices for the introduction of inorganic aerosol particles in air into a flame. Nonflame Sources. A number of devices have been proposed as a replacement for the chemical combustion flame in emission analysis. These devices include t h e plasma torch, plasma jet, high frequency plasma flame and discharges of the hollow cathode type. These devices have instrumental features and applications in common with both chemical flame sources and arc discharge sources, and some overlap of coverage with the review on emission spectroscopy seems unavoidable. Only those devices of most immediate interest to the flame spectroscopist will be described here. The analytical potential of the Langmuir atomic hydrogen plasma torch was investigated by iildous et al. (E). Spectra were obtained for a number of metals introduced as nebulized solutions, but quantitative measurements have not yet been reported. The plasma jet was employed for the analysis of boron tribromide (S5C) and a modification of the nebulizer was claimed (132C) to improve the performance of the plasma jet. A plasma jet for solid samples was described ( S S C ) . Further investigations of the plasma jet have been reported by Czakow et al. (2SC) and Kranz (7SC). Schirrmeister (116C, 117C) investigated interelement effects in the plasma jet. Hoffman and Holdt (56C) described a stabilized arc for high concentration solution analysis. A stabilized low temperature arc for solution analysis has also been described ( 8 3 3 . The temperature of the arc was controlled by introduction of buffers. The arc is said to be quite stable and good detection limits are reported for a number of elements. Among the various types of nonflame sources, the high frequency plasma flame has received the greatest attention during the past tn-o years (SSC, doc, 74C, 86C, 95C). Several papers have appeared which describe fundamental studies of plasma flames. Eckert et al. (3%') reported spectroscopic observations of induction coupled plasma flames in air and argon a t atmospheric pressure. Their discharge was operated a t 4 MHz with a power of about 20 kW. Measured temperatures and electron densities were reported. Armstrong and Ranz (3C) considered the design of inductively coupled plasma sources and investigated a system operating from 15 to 28 N H z . Kalvina (582) investigated the properties of a 9500-LIHz plasma discharge in argon, krypton,
and xenon. T h e electron temperatures and electron concentrations were reported. Lassale and Roig (76C) invest,igated the dependence of intensity on pressure and power for a high frequency discharge. Veillon and Margoshes ( f S 5 C ) and Dickinson and Fassel (SSC) investigated the analyt'ical utilit'y of induction coupled radio frequency plasma sources. Veillon and Margoshes ( f 35C) produced the plasma discharge in argon with a 5 - k R power unit operat,ed a t 4.8 MHz. ,4 pneumatic nebulization system was used with the sample desolvated before introduction to the plasma. Useful emissions were found for several elements which were difficult to atomize with chemical flames, but rather severe interferences were noted. Dickinson and Fassel (SSC) also generated the plasma discharge in argon but employed a 2.5-kW power unit operat,ed a t 30 RIHz. - i n ultrasonic nebulization system \vas employed, and the sample was desolvated before introduction to the plasma. Detect'ion limits for 26 elements were measured and many of these were better than the limits obtained by other techniques. Dickinson and Fassel, unlike Veillon and Margoshes, found the technique to be substantially free of intereference effects. The discrepancy in results was attributed to quite different arrangements for injecting the sample into the plasma. Roodriff ( I 41 C) has commented on t'he difficulties associated with the introduction of a solid or liquid aerosol into a high energy plasma. Borgianni et al. (9C) have examined t'he decomposition processes for metal oxides injected into an argon induction coupled plasma operated a t 4 MHz. The high frequency plasma source was applied to the det,erminations of aluniinurn and molybdenum by Suzuki (127C, l S 8 C ) . Goleb and Middelboe (41C) determined the abundance of nitrogen-15 in small nit.rogen samples by excitation of the nitrogen spectrum in a 100-AIHz discharge. The effect of the noble gases 011 the intensity and duration of the nitrogen spectrum was investigated. Kamada et al. (59C) determined the isotope ratio of oxygen using a microwave discharge method. Kleinniaiin and Svoboda (68C) described a n induction coupled plasma source in which the sample was independently vaporized from an electrically heated graphite support. A 200-W power unit operating a t 40 ILIHz in argon was employed. Measurements were made for a number of elements. It was observed that a decrease of line intensities resulted when NaCl was added to the discharge. Woodriff and Sienier ( l 4 S C ) have employed a capacit'or coupled discharge for excitation of silver vaporized from an electrically heated filament. A unit operating a t
23.8 MHz with a maximal output power of 59.5 W was employed. The discharge was operated in a helium atmosphere. Copper was observed to interfere in the determination. Murayama et al. (91C) investigated the analytical potential of a 2450-MHz discharge produced in a coaxial-line waveguide. The power unit was capable of 400-W output, and the discharge was formed a t atmospheric pressure in argon. Samples were introduced as solutions nebulized by the argon stream. Detection limits were reported for a number of elements. Interference effects were noted when sodium was introduced into the discharge. The spatial distribution of emission in the discharge was investigated and found to be dependent on the element introduced. Aldous et al. ( f C ) used a 2450-MHz discharge to excite spectra from organosulfur and organo-phosphorous compounds mixed with helium at low pressure in sealed silica tubes. Tubes were operated in a 1/4-wave cavity at a power of 40 W. Characteristic spectra were reported. Hingle, Kirkbright, and Bailey (50C) described a low power, 2450M H z device for emission spectroscopy of nebulized solution samples. Interest in the use of the hollow cathode discharge for emission analysis continued in the two years since the last review. Semenova et al. ( f f 8 C )investigated the discharge mechanism in hot hollow cathodes. Xaksimov et al. (78C) used a hollow cathode discharge for the determination of selenium and cadmium in germanium. Pevtsov et al. (94C) described a method of in s i t u chlorination in a hollow cathode discharge which is said to improve the sensitivity of the method for the determination of Ti, Mo, Ta, Zr, and V. Pevtsov et al. (9%') also described the analysis of solution residues. Bueger et al. ( I S C ) investigated conditions for the quantitative analysis of gaseous mixtures of 02, He, Ar, COz and N P . Bueger and Reis ( f 4 C ) described the analysis of iodine in a high current hollow cathode. Bueger and Fink ( f l C , 12C) extended the hollow cathode technique to liquids. Matic and Pesic (84C) used a hollow cathode discharge in the determination of lithium in some refractory oxides. Milazzo and Cecchelli (87C, 88C) explored the potential of a hollow cathode source for measurements in the vacuum ultraviolet region of the spectrum. Rossi et al. ( f f O C , f f f C ) carried out isotopic analyses of uranium with a hollow cathode source. T h e construction and use for quantitative analysis of a lamp which can be operated as a glow discharge or hollow cathode discharge was described by Grimm (4SC). This lamp was primarily intended for samples in the form of metal plates or sheets.
Optical Systems. T h e wide use of Czerny-Turner and Ebert monochromators for flame spectrometry makes two recent papers (89C, I W C ) on multiple diffracted radiation of considerable interest. The problem was treated theoretically and experimentally, and solutions were recommended. Detectors. Most papers concerning detectors have been reviewed 111 the Fundamental Papers section. Topp et al. ( f S S C ) described means of improvement of the signal-to-noise ratio of multiplier phototubes for very weak signals. I n addition to a theoretical treatment of noise in multiplier phototubes and possible methods of reducing it, they described the reduction of the dark current of an EAII 9558QA multiplier phototube by magnetic defocusing of the electrons originating from the inefficient part of the photocathode. They also described the use of a light pipe cone for concentrating the radiation on a small area (2.7-mm diameter) of the photocathode. Larkins et al. ( 7 6 3 described some of the properties of an H T V R166 solar blind multiplier phototube and suggested its applicability in certain areas of flame spectrometry. T o date its applications have been in atomic absorption and atomic fluorescence rather than in flame emission spectrometry. Measurement Systems. Wildy ( f S 9 C ) described a flame emission instrument with provision for electronic integration and automatic background correction. Considerable interest in photon counting for measurement of faint signals was evident during the past two years. These articles have already been reviewed in the Fundamental Papers section. It appears likely that computers ail1 increasingly find application as part of flame spectrometric measuring systems. The use of computer techniques in flame spectrometry was surveyed by Malakoff et al. (79C). Margoshes and Rasberry (SSC) described two procedures for calculating spectrometric analytical functions with digital computers. T o date, flame spectrometric computer use has been limited to processing of the data. Hieftje and Malmstadt (49C) suggested the possibility of a flame spectrometer with computer feedback control utilizing their isolated droplet system. Specialized Instruments. A flame photometer specialized for the determination of Cs was described b y Folsom et al. (S8C). The system consisted of two multiplier phototubes observing the same portion of a flame simultaneously, but each through a different optical filter. One filter passed the Cs 852.11 n m line and the other passed nearby background radiation. Signals from the two phototubes were compared by a differential circuit.
ANALYTICAL CHEMISTRY, VOL. 42,
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Provision was made for automatic sample changing, for rapid comparison of samples and standards, and for monitoring of the aspiration rate. The described procedure was said to allow the determination of Cs in sea water at a concentration of 0.3 Mg/l. with a standard deviation of less than 2%. An instrument for determining Na and K in single cells and nanoliter quantities of biological fluids has been described by Haljamae and Larsso? (45C). This device was said to allow g of K the determination of 6.5 X and 2.2 X g of Na with standard deviations, respectively, of 4.9 and 3.8y0. Sample was introduced to the flame as a solution residue on a fine wire. Signals for the two elements were measured simultaneously by simple phototubes behind the appropriate interference filters. Provision was made for signal integration. The ultramicro flame photometric technique was investigated also by Katz (60C). An instrument for the determination of ultramicro quantities of Na and K was described, and the factors affecting the magnitude of the integrated signal were discussed. Crider et al. (22C) described a flame emission spectrometer for monitoring the concentrat'ion of Fe203 aerosol in animal exposure chambers. Crider (SOC) also described a flame scintillation technique for the measurement of aerosols in air. Pueschel (IOSC) described a flame scintillation instrument for the investigation of the mechanism of decomposition of Ka-containing particles in a flame. Experimental Methods. Sample preparation, nebulization and atomization, interferences, measurement techniques, calibration and calculation, limits of detection, and accuracy and precision will be reviewed. Sample Preparation. Flame spectrometric methods frequently require only a minimal treatment of the sample t,o make it suitable for analysis. Such t,reatment as is required does not differ appreciably from the kinds of sample treatment required for other instrumental measurements. Because the flame technique is most suited t o the analysis of solutions, one of the most common sample preparation treatments is the dissolution of solid samples. X o general discussion of the dissolution process is possible because it must be adapted to the particular requirements of the sample. Two recent examples may be cited (6C, 7 C ) of dissolution procedures for relatively intractable samples. The first described two procedures for dissolving elemental boron for the flame spectrometric determination of impurities. The second described a procedure for dissolving silicon oxide films on silicon surfaces for the 216R
determination of Na contamination of the film. From a knowledge of the rate of dissolution of the silicon oxide film, it was possible to determine the distribution of sodium in the film. The sample dissolution step was avoided in some cases. Crider et al. (IdC) and Pueschel (IOSC) introduced atmospheric aerosol particles directly into the flame. Lebedev ( 7 W ) utilized the procedure first described by Gilbert of nebulizing suspensions of powders. Lebedev investigated the effect of several variables on the determination of alkali metals in minerals. He found that the emission intensity was always less than for solutions of comparable concentration, but that the precision was equally good. It was necessary to control the particle sizes, and the alkali metals were found to evaporate differently from different minerals. Pueschel (1OSC) also found variation in the rate of production of S a from particles of compounds such as NaCl, KaBr, and Na2S04 introduced to the flame. A procedure for determination of atmospheric sulfuric acid aerosol by flame photometry was also described (115C). I n this latter case, considerable treatment of the sample preceded the measurement. The sample was collected, separated from other sulfates, and converted to sulfur dioxide before introduction to the flame. For solution samples, a separation and/or concentration step is frequently desirable. Solvent extraction continues to be the most widely used technique for both purposes. Among recent papers are the following which described the use of the solvent extraction technique in the flame emission determination of Mo ( f d 9 C , ISOC), R h ( S I C ) , As (SOC), and R h and P d (15C). The danger of contamination in sample treatment was made strikingly evident by Robertson (108C). He examined possible sources of contamination in trace element analysis of sea water by use of an activation analysis method. The concentration of 10 trace elements in a variety of solvents, reagents, and other materials, such as rubber tubing, nylon, and polyethylene, was reported. Robertson correctly pointed out that his measurements did not indicate the rate a t which the impurities entered the sample, but they did indicate the potential hazard. Of particular interest to flame q ~ e c troscopists was the information on the concentration of trace elements in a number of reagents used in solvent extraction procedures. Nebulization a n d Atomization. Koirtyohann and Pickett (71C) and Zeegers, Townsend, and Winefordner (144C) estimated the efficiency of free atom formation for a number of elements in premixed flames. The atomization process in premixed, fuel-rich
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
02/C2H2 flame was investigated by Cowley, Fassel, and Kniseley (19C). The results of the latter study made it clear that the enhancement of both emission and absorption observed in such flames was largely due to the favorable chemical environment found in the interconal zone. Interferences. Smith, Stafford, and Winefordner (12SC) investigated interference effects occurring in the ilrlentrained air/Hz flame. Total consumption burners were used. They found that, except for ionization effects, interferences were increased in this rather cool flame compared to higher temperature flames. Smith and Winefordner (121C)reinvestigated the effect of phosphate on the calcium emission signal in turbulent 02/H2 and iirlentrained air/Hz flames and laminar acetylene-air flames. The laminar flame was found to be relatively free of interferences. Interference effects with Ca were studied by Pleskach et al. (1OOC, l o l C ) , Spitz et al. (124C), Pungor and Szasz (lOgC, 105C), and Rocchiccioli and Townshend (109C). Evans and Grimshaw (347) described the use of La and sulfuric acid to suppress interferences in the determination of Ca in soil extracts. Mansell (80C) discussed the thermodynamic stability of alkaline earth osides and aluminates in flame spectrometry. Other studies of chemical interferences included the following (IOC, 57C, 9 9 0 . Sastri, Chakrabarti, and Willis (11SC, 114C) attempted to demonstrate that formation of refractory oxides in the flame proceeded largely through retention of metal-oxygen bonds existing in the sample solution. They compared absorbances obtained from solutions of simple salts of the metals and solutions of metallocenes and found a considerable enhancement for the metallocene solution in which no metal-oxygen bonds exists in the solution. Fassel and Becker (S6C) demonstrated the availability of premixed high temperature flames makes discussion of interferences of the calcium-phosphate type largely academic. The disappearance of the phosphate interference in the flame employed was attributed to the production of smaller aerosol particles, higher flame temperatures, and longer residence times in the flame. The results of others would seem to corroborate the findings of Fassel and Becker. Harrison and Wadlin (4SC) found that interferences in the determination of l l g can be largely eliminated by use of a N20/C2H2 flame. Atwell and Hebert (4C) similarly concluded that use of K20/C2H2 flames eliminated interferences in the determination of Rh. Koirtyohann and Pickett (70C) have reported the observation of a new type
of interference in the premixed NzO/ C2Hz flame. An enhancement of the emission and absorption signals of a number of elements was noted in the presence of mineral acids and salts when the burner slot was aligned with the optical axis. The enhancement effect did not appear when the slot was perpendicular to the optical axis. Koirtyohann and Pickett found that the spatial distribution of the atoms within the flame was altered by the additives. Kirkbright and Wilson (67C) have described a technique for attenuating spectral interference from resonance lines. Pickett and Koirtyohann (96C) neatly summarized causes of interferences and means of dealing with them. Measurement Techniques. T h e past two years have seen increased activity in t h e use of both higher temperature flames (N20/CzH2) and lower temperature flames. Investigations dealing with the N20/CzHz flame have already been touched upon in the section on Instrumentation. Pickett and Koirtyohann (72C, 97C, 9%') have dealt most extensively with the use of the N20/C2H2 flame for emission analysis. They have described the general characteristics of this source and reported detection limits for 34 elements (9"). They investigated in more detail the use of this source in the emission determination of Li and the alkaline earth elements (72C) and Al, Ga, I n , T1, Ge, and Sn (98C). Results for the rare earth elements have been reported by Kniseley, Butler, and Fassel (69C). Lower temperature flames were chiefly of intereqt for determinations based on emission from molecular species. Much of the emission seemed to be chemiluminescent. Largely the elements determined in cool flames were those, such as the nonmetals, which gave no useful atomic emission in a conveniently accessible region of the spectrum. The low temperatures encountered using such flames increased the occurrence of chemical and solute vaporization interferences. Dagnall, Thompson, and West (26C) have employed a KZ/H2diffusion flame in the emission determination of phosphorous. The emitting species was identified as HPO. The detection limit was found t o be 0.1 ppm phosphorous. Nobt cations interfered and use of an ion exchange method to convert phosphates to orthophoqphoric acid was recommended. Syty and Dean (129C, I S l C ) described the determination of phosphorous and sulfur in a shielded, reversed air/Hz flame. The emitting species measured were H P O and Sz. Detection limits were reported to be 6 pg/ml and 5 pg/ml for phosphorous and d f u r , respectively. Dagnall et al. (28C) also used a Nz/Hz diffusion flame for the determination
of Sn a s the SnH species with a detection limit of 1.5 ppm Sn. A method for the determination of chloride, bromide, and iodide was described by Dagnall et al. (29C). This method utilized the intense band emission observed for the halides in the presence of indium in the cool Nz/Hz diffusion flame. The emitting species has been identified as InX. Detection limits for chloride, bromide, and iodide were reported to be approximately 0.7, 1.6, and 2 ppm, respectively. Indium chloride band emission was also used by Gutsche, Herrmann, and Rudiger (44C) for the determination of organic chlorides in the analysis of pesticide residues. They used an apparatus similar to that described some time ago by Gilbert in which an insert of indium metal in the burner was used to supply the indium responsible for the band emission. A detection limit of 0.23 pg of lindane, corresponding to 0.16 pg of C1, was reported. Gutsche and Herrmann (43C) also described a simplified procedure using a filter photometer. With this procedure, the detection limit was reported to be 0.006 pg lindane (0.06 pg chlorine). Herrmann and Gutsche (4SC) have reported a further development of the method. Crider (W1C) reported the emission spectrum for a number of organic halides introduced into hydrogen-air flames. Parsons (92C) measured the relative emission intensities of C H and Cz for a number of normal and branched alcohols introduced into a hydrogen-entrained air flame. He suggested the possibility of qualitative analysis based on the variation of C H and C2 intensity with structure. This possibility has also been investigated by Dagnall et al. (25C). Calibration and Calculation. Shatkay (119C) considered some of the errors which may be associated with the usual techniques for relating spectrometric response to analyte concentration. H e considered possible errors in the use of the analytical curve method and the method of standard additions when strongly interfering substances were present in the sample solution. H e described a method of avoiding errors of this type. Barnett, Fassel, and Kniseley (6C) considered the theoretical principles of the internal standardization technique. Included in their study were the effect on the line intensity ratio of excitation energy, ionization energy, partition functions, and electron density. It was concluded that in choosing an analytical line pair, the most important factors were excitation energies, degree of ionization, and partition function behavior. The discussion was most pertinent to high temperature sources, such as the induction coupled plasma. An interesting type of internal stan-
dardization was discussed by Skogerboe, Todd, and Morrison (12OC). I n this technique the intensity ratio of component lines of a multiplet of an element was plotted us. concentration. Over a certain range of concentrations of the two lines with different oscillator strengths, their intensities were affected to different extents by self-absorption and the intensity ratio would vary with concentration. With this technique, the element in many respects served as its own internal standard. It was demonstrated for several examples that the intensity ratio was largely insensitive to changes in fuel flow rate, flame region viewed, and solute vaporization. Limits of Detection. Limits of detection must be employed with some discretion, b u t , despite a n y shortcomings, a detection limit reported for clearly specified conditions is t h e most useful single quantity available in assessing the potential utility of a method for determination of a given element. A useful list of flame emission detection limits obtained under uniform conditions were reported by Pickett and Koirtyohann (72C, 97C, 98C). Detection limits and determination limits for the rare earth elements were reported by Kniseley, Butler, and Fassel (69C). Measurement conditions were nearly identical to those of Pickett and Koirtyohann. Christian (17C) also reported detection limits for similar conditions, but his limits are surprisingly very much higher that those of Pickett and Koirtyohaiiii and Kniseley et al. Accuracy and Precision. Factors affect'ing t h e accuracy and precision of flame emission and flame at,omic absorption spectrometry were investigated by Boettner and Grunder (8C). For flame emission, they found the burner to be t'he component which has the most significant effect on the precision. They found it possible to maintain a long term standard deviation of 3 to 5% for the analysis. Rains and Menis (106C) described a system with which they were able to carry out flame emission analysis with standard deviations of 1% and better. Instrumental components were optimized and a differential measurement, technique was used. 'The differential measurement technique was analogous to the scale-expansion technique frequently employed in spectrophotometry of solutions, L e . , the instrument was made to read zero for a sample of finite concentration and to read full scale for a sample of any selected higher concentration. ATOMIC ABSORPTION SPECTROMETRY
Instrumentation. Radiation iources, flameless atomization technique?, and the same topics reviewed i n the atomic
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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a n d molecular emission spectrometry section will be reviewed here. Radiation Sources. Hollow cathode discharge tubes are commercially available for most of t h e elements and continue t o be the most popular radiation source for atomic absorption spectrometry, b u t a number of recent papers have suggested changes in t h e design of hollow cathodes or substitution of other kinds of radiation sources for atomic absorption. T h e papers dealing with the mechanism of excitation and characteristics of the discharge of hollow cathode tubes are given in the Fundamental Papers section. Two papers described demountable hollow cathode lamps. The design of Popham and Schrenk (1070, 1080) was reported to give performance equivalent to commercially available lamps, and, therefore, its chief virtue was economy. Rossi and Omenetto (1220) described a demountable water-cooled hollow cathode lamp which could be operated a t currents u p to 500 mA. A modified hollow cathode which gave increased line intensity without appreciable line broadening was described by van Gelder ( 4 2 0 ) . This tube was similar in principle to the high intensity lamps in that the sputtering and excitation functions are separate, but the electrode arrangement was different. Two power supplies were required, Schrenk, Meloan, and Frank (129D) operated a hollow cathode lamp in a magnetic field to seek to broaden the lines and thereby increase overlap with noncoincident absorption lines. Interest in microwave-excited electrodeless discharge lamps was stimulated by the requirement for high intensity sources for atomic fluorescence, but it rather quickly became apparent that electrodeless lamps could be of considerable utility in atomic absorption as well. The preparation, operation, and characteristics of electrodeless lamps have been discussed in the Fundamental Papers and the iltomic Fluorescence Spectrometry sections. The use of electrodeless discharge lamps in the atomic absorption spectrophotometric determination of thallium and mercury has been described by Browner, Dagnall, and West ( 2 2 0 ) . Browner et al. ( 2 1 0 ) have also described a method of electronically modulating the output of electrodeless discharge tubes. Bache and Lisk (SD) described a simple device for improving the tuning of a tapered waveguide in operating electrodeless discharges. Rann ( l l 4 D ) has taken another look a t the utility of a flame as the radiation source for atomic absorption measurements. From both a theoretical and experimental treatment he concluded that the sensitivity was reduced by 218R
approximately a factor of two if a flame replaced a hollow cathode source. Strasheim and Human (1S8D1 1590) investigated the use of a time resolved spark as a primary light source for atomic absorption spectrometry. The most appealing feature of this source was its convenience for simultaneous multielement analysis by atomic absorption. Strasheim and Human (1S9D) demonstrated its utility for this purpose. The chief disadvantage of this source was the rather poor precision achieved. A gas stabilized dc arc, described by Human, Butler, and Strasheim (560) offered the same convenience as the time resolved spark for multielement analysis, and the precision was as good as with hollow cathode lamps as primary sources. The sensitivity was somewhat poorer than that achieved with hollow cathode sources. A high frequency plasma torch was used ( 4 4 0 ) as the primary source for atomic absorption spectrometry. An interesting survey of available light sources over the wavelength range 150 nm to 20 p was given by Cann (260). This survey contained a great deal of information on the spectral output of sources that was not readily available elsewhere. Flames and Burners. The desirable characteristics of flames a n d burners are t h e same for both emission and absorption measurements and, therefore, the greater part of the discussion of flames and burners in the section on flame emission applies equally well t o flame atomic absorption. This section will include only those papers which bear more directly on atomic absorption, and the reader must refer to the earlier section to complete the discussion of this subject. Higher temperature flames have been of considerable interest for atomic absorption as well as flame emission. Willis (1540) gave a thorough review of the subject of high temperature flames for atomic absorption spectroscopy. Shifrin, Hell, and Ramirez-Munoz (1SID)presented some results for atomic absorption with the heated chamber NzO/C2Hz burner. Butler and Fulton ( 2 4 0 ) investigated the analytical utility of flames providing temperatures between those of air/CZH* and NzO/CzHz flames. A CzH2 flame supported with mixed N20-air can be varied continuously from one temperature extreme to the other. The results seemed to indicate that for most applications there were no advantages significant enough to justify the additional complexity of gas mixing. Rubeska and Moldan ( l % + D1250) , reported on further investigations of longpath absorption tubes of the type first described by Fuwa. I n their work, the tube was additionally heated in a fur-
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
nace. Employing air/Hz and 02/Hz flames they studied the effect of experimental variables on the sensitivity of determination of a number of elements, such as M g and Sn, for which difficulty with oxide formation might be anticipated. I n all cases, the best sensitivities were obtained for fuel rich conditions. Under these conditions, a separated flame was obtained] with secondary combustion occurring a t the end of the tube. Hingle, Kirkbright, and West ( 5 4 0 ) also described a long tube separated flame device for atomic absorption. Their apparatus differed from earlier arrangements in several respects. Principally, a premixed air/CzHz burner was used, and the burner was sealed to the system in such a way that no entrainment of air occurred. Ando et al. ( 2 0 ) found that the determination of As with the long tube burner could be markedly improved by dilution of the flame with Nz]Ar, or He. The background flame absorption, which was severe a t the most sensitive As resonance line, was reported to be greatly reduced by the addition of inert gases. Most atomic absorption determinations were carried out with C2Hzflames supported by either air or N20. Hydrogen flames may, however, offer advantages for some elements. Schallis and Kahn ( 1 2 7 0 ) have pointed out the situations in which use of an air/Hz flame should be considered. These include: (a) when the absorption line lies between 200 and 230 nm, because background absorption of the air/Hz flame was considerably less than that of the air/CzHz flame in this region, and (b) when lower temperatures were required to avoid ionization effects. The Ar/ entrained air/Hz flame has much the same characteristics as the air/Hz flame, and has been found useful in improving the detection limits for several elements (6SD).
Kirkbright, Sargent, and West (71D ) described a burner for producing a 5 cm long air/CzHz flame which was shielded from atmospheric entrainment by a flow of nitrogen. This arrangement resulted in an improvement of the background absorption and noise observed a t short wavelengths. This burner was used by Kirkbright et al. for the determination of As and Se. Bleekrode (IOD, 11D) described the apparatus employed in measuring the absorption of iron in a low pressure OZ/ CzHz flame. The reduced flame noise observed when a single-slot burner was replaced by the three-slot Boling burner was explained ( I Z D ) as being due to a much larger optically homogenous region in the flame above the burner. Two unusual combustion flames were recently discussed. Miaud and Robin
(990) have further investigated the technique introduced by Venghiattis of using a solid propellant mix to produce the flame. Bailey and Rankin (50,6 D ) investigated the use of organic liquids as fuels for flame spectrometry. Kahn, Peterson, and Schallis ( 6 2 0 ) described a novel means of introducing sample to the flame which they call the “sampling boat” technique. The sample was placed in a small tantalum boat, solvent evaporated, and the boat then placed in the flame of a Boling burner. The more volatile elements were quickly vaporized with, in some cases, a substantial improvement in detection limits compared to aerosol introduction techniques. Crawford and Greweing (SOD) added a stream splitting device t o the sample port of a premix nebulizerburner system to allow automatic sample dilution. Flameless Atomization Techniques. A number of alternatives exist to t h e usual practice of atomization of samples b y introduction of a n aerosol of the sample t o the hot gases of a combustion flame. Brandenberger (16D) and Brandenberger and Bader (17D) described a technique in which the element of interest was first plated on a wire and then volatilized into a cell in the optical path of a n atomic absorption spectrometer by electrical heating of the wire. This technique was reported to have been successfully employed in the determination of Hg, Cd, Zn, Pb, Te, Cu, Ag, Au, and Pt. West and Williams (15 5 0 ) vaporized samples from a heated carbon filament without prior reduction or separation of the element of interest. Sample solution was placed directly on the filament, solvent was removed, and the filament was heated to 2000-2500’ C in a n inert atmosphere by passage of a current of about 100 A a t 5 V. Results were reported for the determinations of silver and magnesium. The absorption detection limits were reported to be g for both silver and magnesium. The relative standard deviation was reported to be 9% for magnesium in the range of 1-5 X g and 15% for silver in the g. Interelement range 1-10 X effects were not investigated. Massmann ( 9 5 0 , 9 6 0 ) continued to investigate atomization of samples from a graphite crucible electrically heated in a n argon atmosphere. He reported detection limits with this technique for 16 elements. Detection limits ranged from 2 ng for Se to 5 x 10-4 ng for Mg. L’vov et al. ( 6 4 0 , 67D, 7 9 0 - 8 6 0 ) reported a number of further measurements with the graphite cuvette technique. These included a general discussion of the method (??OD), correction for background absorption (??lo), and a n integration-measurement technique (82D), and determination of Cd (64D), I (83D), P ( 8 5 0 ) and Zn and
Cd in radioactive mixtures (840). A spectrometer for use with the graphite cuvette has also been described (67D). The present status of this work was recently discussed by L’vov (79D). A list of detection limits was included in this latter article. Woodriff et al. (1560-159D) described a high temperature furnace method for atomization of samples for atomic absorption. I n their arrangement, a long graphite tube was heated in an argon atmosphere by passage of current from an electrical arc welder. Temperatures u p to 3000’ C are achieved. Samples were introduced as nebulized solutions or as solids through a side arm near the middle of the tube. Detection limits were reported for 15 elements. The limits ranged from 5 X 10-1 to 1 X lo-* ng for All Dy, Ho, and E r as well as some of the more readily atomized elements. A number of papers in the past described the use of a hollow cathode discharge for the atomization of samples for atomic absorption spectrometry. Yokoyama and Ikeda (1640) reported a modification of this technique in which the discharge was pulsed and absorption was observed during a selected time interval after the initiation of each pulse by using a pulsegated photomultiplier. Absorption was found to decay rather slowly and persisted some time after disappearance of the emission spectrum. A time resolved atomic absorption technique was also briefly reported b y Kantor and Erdey (65D). I n their work a pulsed arc was employed for atomization of solid samples. A rotating disk was used as the time resolving element, and spectrographic detection was employed. The rf plasma torch was employed (15D, 440, l49D, 150L)) for sample atomization for atomic absorption. X decision as to the utility of this device in atomic absorption awaits further investigation. Karyakin and Kaigorodov (66D) further investigated the use of a pulsed laser for atomization of samples for atomic absorption measurements. They used continuous radiation emitted from the laser-produced crater as the primary sources for the absorption measurement. The de arc discharge was also employed (7D) for sample atomization. The measurement precision is somewhat less than satisfactory. Marinkovic et al. (9SD) described a low temperature stabilized arc for atomization of solutions for atomic absorption. I n a brief note (123D), atomization of samples by electron bombardment was described. Optical Components. Sullivan and Walsh (l4OD) have provided a useful and interesting review of the “resonance monochromator” and “selective modulation]’ techniques. Lowe (78D) de-
scribed a recent modification of the selective modulation technique. The selective modulation technique was utilized in the determination of Au, Pt, Pd, and R h (l48D). Kahn ( 6 1 0 ) described a system for background compensation in atomic absorption measurements. This system alternately passed light from a deuterium arc, and from a hollow cathode lamp through the flame. The ratio of the two signals was read. Snelleman (157D) described a method for rapid scanning of a small portion of the spectrum around the absorption line. A continuum primary source was used, and a vibrating mirror in the optical path between the dispersing element and exit slit caused a small portion of the spectrum to vibrate across the exit slit of the monochromator. Such a system automatically compensated for broad band background absorption and reduced the noise due to fluctuations in source intensity. Equations for the theoretical detection limits with this system were derived and discussed. Svoboda (141D) described a device which accomplished much the same purposes as Snellernan’s system but was quite different in design. Svoboda’s system employed an oscillating interference filter for modulation of the absorption line. Detectors. See the corresponding section in the Emission portion for articles concerning det’ectors. Measurement Systems. .i logarithmic converter using a silicon transistor in the feed-back loop of a n operational amplifier circuit was described (1010). This converter w s designed for use with the Perkin-Elmer 303 atomic absorption spectrophotometer but should be adaptable to other instruments. Harrison and Berry ( 4 9 0 ) described a n analog integrator for use with the Perkin-Elmer 303. Further pertinent information will be found in the Emission section. Special Purpose Instruments. Simultaneous multielement atomic absorption spectroscopy continues to be of considerable interest. Mavrodineanu and Hughes (97D) described a system for simultaneous multielement analysis in which the characteristic radiation from hollow cathode tubes was combined into a single, collimated polychromatic beam and passed through the flame into a conventional dispersing system. The polychromatic beam was obtained by performing the dispersion experiment in reverse. Each source was placed a t the position which would normally correspond t’o t’he exit slit position of a monochromator for the desired wavelength and the polychromatic beam emerged a t the position which would normally be the entrance slit,. Provision was also made for
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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simultaneous flame emission measurements. Walsh (1510) discussed a number of possible arrangements for simultaneous multielement analysis, with particular emphasis on systems employing resonance detectors. Brech described instruments for rapid sequential multielement analysis ( 1 8 0 ) and for simultaneous multielement anaylsis (19D). Ling (77D) designed an atomic absorption spectrometer specifically for the determination of nanogram quantities of mercury. Experimental Methods. T h e same topics reviewed in the section on atomic and molecular emission spectrometry will be reviewed here. Sample Preparation. T h e sample preparation requirements for atomic absorption are identical with those for flame emission, and only a few additional examples of procedures will be included in this section. T h e bibliographies of the Slavins (ISSD, 1 3 5 0 ) are the best sources of information for papers describing sample preparation procedures for specific types of samples. The decomposition of silicate materials for atomic absorption analysis has received a surprising amount of attention during the past two years. Four groups (9D, 75D, IOSD, 14rD) independently published procedures for the decomposition and analysis of silicates. Langmyhr published a series of eight papers, only the first of which is cited (75D), on the subject during the current review period. Scholes (1280) published a review of procedures for the atomic absorption analysis of iron and steel. Numerous papers reported procedures for biological samples. T o cite only a few examples, procedures were reported for the digestion of brain and hair (4D), human hair ( 5 1 0 ) , sugar beet leaves (4SD),and wool (52D). I n contrast to the extensive sample preparation described in some of the above examples, several recent papers described atomic absorption analysis of samples with little or no prior treatment. Iron has been determined in nitrogen tetroxide (1650) by direct aspiration of liquid nitrogen tetroxide into the flame. Molybdenum hexafluoride in uranium hexafluoride has been deterniined (2260) by direct introduction of the gaseous uranium hexafluoride into the flame of a premix burner. Silver in air has been determined (37D) by addition of the silver-containing air stream to the primary air supply of the burner. Other procedures were also described for determination of gas phase samples. Holak ( 6 6 0 ) has determined As as arsine. I n his procedure, the As present in the sample was converted to arsine, the arsine was trapped a t liquid nitrogen temperature, and, after warming to 220R
*
room temperature, a flow of nitrogen was used to sweep the arsine through the sample port and into a premix burner. Hatch and Ott (53D) determined mercury by sweeping mercury vapor through a quartz cell in the optical path of an atomic absorption spectrometer. The technique of Brandenberger and Bader (17D) for mercury and other volatile metals was described in the section on Instrumentation. Solvent extraction for separation and concentration is one of the most commonly employed sample treatment procedures. Extraction procedures were described in detail in numerous papers on the application of atomic absorption to specific analysis problems. Some recent examples included extraction of Ca ( l @ D ) , Au (45D, 4 6 0 , 165D), Co and Zn (35D),and trace elements in calcium sulfate minerals (58D). Law and Green (76D) discussed the applicability of solvent extraction procedures in the presence of emulsion-forming residues. Munro (102D) investigated the effect of acidity and extraction ratio on extraction procedures. Giraud and Robin (43D) investigated the effect of organic solvents on atomic absorption measurements. Several recent papers described ion exchange procedures for isolation and concentration of trace elements. Anion exchange resins were used to separate Sn, Cd, and Zn from Cu (87D), Ag in fresh water (28D), and Au in fresh water (27D). Chelating ion exchange resins were employed (1180) to concentrate trace elements in sea water and separate them from the major components. Mislan and Elchuk (1000) described a procedure for preconcentration of samples by continuous evaporation with a rotary evaporator. A preconcentration factor of 70 was found to be the practical limit. Nebulization and Atomization. Takada and Nakano (l4SD-2460) investigated the effect of the nebulization system on the sensitivity of atomic absorption measurements. Factors investigated included spray chamber size, shape, and temperature, temperature of the air used for nebulization, and solution flow rate. Reinhold, Pascoe, and Kfoury (117D) found the internal diameter of the sample capillary tubing to have a critical effect on the aspiration rate of serum and plasma. The “sampling boat” technique was found (S1D) advantageous for atomization of T1 in blood and urine. Increase of 25-fold in sensitivity was reported compared to aspiration of the sample. Interferences. There appears t o be a n unfortunate tendency in many atomic absorption papers to rediscover interferences observed long ago in flame emission analysis. I t is worth repeating t h a t any process t h a t affects the atomic concentration in
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
the flame affects flame emission and atomic absorption measurements t o t h e same extent and requires t h e same remedy in either case. Interferences which affect both emission and absorption measurements have been included in the section on Emission. Harrison and Juliano (50D) observed that a variety of organic solvents depress the absorbance of Sn in a premixed air/Hz flame. They suggested that this effect was due to the removal of atomic H from the flame by organic radicals. Further evidence would seem desirable before this suggestion is accepted. A number of additional examples of spectral interferences in atomic absorption measurements were reported. Hall and Woodward (47D) observed that a high concentration of Cu interfered in the d@ermination of P b when the P b 2170 A line was observed. Further examples have been reported of the overlap of the absorption line of one element with the emission line of another element. Fassel, Rasmuson, and Cowley ( 3 8 0 ) first pointed out that the likelihood of occurrence of this type of interference had been considerably underestimated. They reported several examples of line overlap interferences: Eu on Cu a t 324.7 nm, P t on Fe at 271.9 nm, V on Si a t 250.7 nm, V on A1 a t 308.2 nm. Additional interferences of this type were reported by Slavin and Sattur (lS4D) for P b on Sb a t 217.0 nm, by Manning and Fernandez (92D) for Co on Hg a t 253.7 nm, and by Allan (1D ) for Ga on M n a t 403.3 nm. Measurement Techniques. A large number of papers described t h e application of atomic absorption t o t h e determination of specific elements. I n this section, only a few examples are given of the application of conventional atomic absorption techniques, and greater attention is devoted t o t h e more novel approaches, such as indirect methods and isotope analysis. Popham and Schrenk have further investigated the atomic absorption determinations of Ga and I n (llOD) and Ge (109D) The determination of As has been investigated by Menis and Rains (98D). Chakrabarti ( M D ) has described the atomic absorption spectrometry of Se. Makarov and Kukushkin have investigated the determination of I r ( 8 9 0 ) and R u (9OD),and have Oslinski and Knight (lo@) determined Os. Feldman, Blasi, and Smith ( 3 9 0 ) have briefly described the use of atomic absorption techniques for the determination of major constituents (5% or greater), An internal standard method was employed. Burgess and Donega ( 2 3 0 ) have used an atomic absorption technique to determine the partial pres-
sure of N a present in quartz tube furnace atmospheres. Two independent reports of the atomic absorption determination of the isotopic concentrations of lead have appeared. Kirchhof ( 6 9 0 ) measured the concentrations of P b 206 and P b 208 using the absorption of Jhe hyperfin? components of the 4058 A and 2833 A lines. Samples and standards containing known isotopic mixtures were incorporated into hollow cathode discharge lamps which were used as primary radiation sources. The concentration of the individual isotopes was determined by measuring the absorption of isotopically pure vapors. A hollow cathode-type discharge was used to produce the absorbing vapor. Agreement with mass spectrometric data was reported to be within 2%. Brimhall ( 2 0 0 ) measured the concentrations of lead-206, -207, and -208 in solutions using the hyperfine components of the 283.3 n m line. A standard atomic absorption system was used, but three hollow cathodes, each enriched in one of the isotopes, were used, and standard solutions of known isotopic composition were prepared. From the absorptions measured with the three lamps, the isotopic concentrations of a n unknown were calculated by solving a set of three simultaneous equations. Agreement within 2% was reported. A number of recent papers described indirect atomic absorption techniques. Boltz et al. reported the largest number of applications of this technique, and the majority of these are based on the measurement of the atomic absorption of Mo. The indirect determinations of P and Si ( 5 7 0 ) were reported. The molybdophosphoric and molybdosilicic acids were formed in solution, separated from each other and from excess molybdate by solvent extraction, and the concentration of molybdenum was subsequently measured. Concentrations of P and Si were calculated from the measured M o concentrations. Similar procedures have been described for V (59D), T1 and NH3 (340), and As (330). Kirkbright et al. have used similar procedures for the determination of ?Jb ( 7 2 0 ) , T h ( 7 0 0 ) , and T i (7'3D), and Ramakrishna, Robinson, and West (1110) have described a procedure for P, As, and Si. Sheridan, Lau, and Senkowski (13 0 0 ) determined the concentration of nonionic surfactants by precipitation of the surfactant as a heteropoly phosphomolybdic acid-barium complex and measurement of the remaining molydenum. Sulfur dioxide was determined (1810 ) by conversion to sulfate and atomic absorption measurement of lead remaining after precipitation of lead sulfate. Sulfate was also determined ( 3 6 0 , 8 8 0 ) by measurement of excess barium after barium sulfate precipitation. Sulfite
was determined (60D) by atomic absorption measurement of mercury, and chloride has been determined (116D) b y measurement of silver. Phthalic acid was determined (7'40) by solvent extraction with neocuproinecopper chelate and subsequent determination of copper. Methods based on the measurement of copper have also been described for the determination of thiocyanate (32D), nitrate (1630), and perchlorate (29D). A similar procedure was employed for the determination of mercury (160D) by measurement of the atomic absorption of zinc. Vitamin B12 was determined ( 8 0 ) by the measurement of cobalt absorption. The indirect determinations of iodine (1680) and phydroxy naphthoic acid (1610 ) were also reported. A somewhat different type of indirect determination was based on the enhancement or depression effect of a species on the atomic absorption of a selected element. Bond and O'Donnell (130) have shown that fluoride can be determined by observation of its depression of the absorption of magnesium, or enhancement of the absorption of zirconium or titanium. Bond and Willis ( 1 4 0 ) used the enhancement of the atomic absorption of zirconium for the determination of ammonia. The accuracy of the various indirect methods has been discussed by Pleskach (1060). Flame molecular absorption has been employed for the determination of sulfur in amino acids b y Fuwa and Vallee (410). Absorption due to SOs was measured. A hydrogen discharge primary source and Fuwa long tube burner were used. A detection limit of 10 pg was reported. Calibration a n d Calculation. Smith, Blasi, and Feldman (13 6 0 ) described adaptation of the internal standard method to atomic absorption measurements. A t least two-fold improvement in precision is reported. The internal standard method was used by Katskov and L'vov (680) with the graphite cuvette technique. Rann (11 5 0 ) investigated absolute atomic absorption measurements. A t the present state of development of atomic absorption, this work was of relatively little analytical use (see Fundamental Studies section), Treatment of atomic absorption analytical data by digital computer was described by Wendt (1520) and Marshall (940). Malakoff, RamirezMunoz, and Scott (910) discussed computer techniques for simultaneously following the effect of two independent variables on the absorption signal. Ramirez-Munoz (11 2 0 ) discussed the application of sensitivity diagrams to atomic absorption measurements, and Ramirez-Munoz and Brace (11S D ) derived an expression for the dynamic range of atomic absorption.
Limits of Detection. T h e most complete a n d up-to-date listings of atomic absorption detection limits are t o be found in the literature supplied by the manufacturers of atomic absorption equipment, e.g., t h e recently revised Perkin-Elmer looseleaf methods book (1050). Fiorino et al. (400) have reported detection limits for 14 elements in premixed acetyleneoxygen and acetylene-nitrous oxide flames. The definition of detection limit has been further considered by Shifrin and Ramirez-Nunoz (13 2 0 ) Accuracy and Precision. Roos (1800) investigated the relationship between transmittance reading and precision for atomic absorption. He found that for some cases the uncertainty in transmittance was independent of transmittance, but for others the uncertainty was proportional to T log T . I n either case, the optimum concentration range was found to be approximately 20 to 200 times the sensitivity of the analyte. An interlaboratory studjr was reported (1190) for the atomic absorption determination of zinc in foods. For zinc contents from 5 to 60 ppm recoveries of 98 to 1027, and standard deviations of 0.2 to 3 ppm were reported. ATOMIC FLUORESCENCE SPECTROMETRY
The majority of the articles on atomic fluorescence are concerned with flames, sources, and theory, but relatively few are concerned with applications. The total number of scientific paperq on atomic fluorescence is rather small, and so this section of the review will be divided differently than the preceding two sections on flame emission and atomic absorption. The majority of the papers published within the past two years have been concerned with the development of sources and flamer to improve detection limits. In the first part of this section, detection limits (for aqueous solutions unless otherwise stated) are given for elements in each group of the periodic table for a variety of experimental conditions in atomic fluorescence flame spectrometry. I n the second part of this section, a variety of other studies involving atomic fluorescence are mentioned. Analytical Results in Atomic Fluorescence Flame Spectrometry
Group Ia Elements. The atomic fluorescence of alkali elements is of academic interest only. Fluorescence quenching studies have been carried out by several and are listed in the Fundamental section. h s far as t h e authors know, no an:tlgtical studies have yet been performed. Xldous, Dagnall, and West ( 2 E ) have described the glass and preparation procedure for electrodeless discharge tubes (abbre-
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
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viated EDT hereafter) of the alkali metals. Burling, Czajkowski, and Krause (l9E)also described the preparation of rf powered EDT’s for the excitation of atomic fluorescence. Group IIa Elements. T h e resonance lines of the alkaline earth elements studied b y atomic fluorescence spectrometry are: Be, 234.9 nm; Mg, 285.2 nm; Ca 422.7 nm; Sr, 460.7 nm. Beryllium has been studied by Hingle, Kirkbright, and West (28E), Rob’inson and Hsu (4OE), Bratzel, Dagnall, and Winefordner (YE). The first group obtained a detection limit of 0.01 pg/ml using a premixed IUZ/OZ/CZH~ flame and an EDT (prepared as iodide or chloride). The second group obtained a detection limit of 0.5 pg/ml using a premixed N20/C2H2 flame produced with a special multislot burner and a high intensity hollow cathode discharge tube (abbreviated H C D T hereafter). The last obtained a detection limit of 0.04 pg/ml employing a premixed fuel rich N20/ C2Hz flame produced using a total consumption burner. The fluorescence signal as a function of flame height was also investigated in the latter study. The best detection limit above is about 10-fold poorer than the best atomic absorption value previously reported. Magnesium has been extensively studied by atomic fluorescence. Because quartz EDT’s are subject to attack by magnesium vapor (even if present in E D T as iodide), most studies have involved the use of high intensity HCDT’s and continuum sources. Xevertheless, Zacha et al. (51E) obtained a detection limit of 0.008 pg/ml using a turbulent hrlentrained air/Hz flame and an EDT (prepared from the iodide). Smith, Stafford, and Winefordner (44E) obtained 0.01 pg/ml with a similar system and 0.1 pg/ml in jet engine oils, West and Williams (49E) detected 0.001 pg/ml using a high intensity H C D T with optimized currents and either a premixed air/propane flame or air/Hp flame. Demers and Ellis (24E) obtained a detection limit of 0.04 pg/ml using a turbulent entrained air/ HZflame and a 450 watt xenon arc lamp. Similar interferences as in atomic absorption studies were found in the latter studies. Manning and Heneage (323) obtained a detection limit of 0.1 and 0.01 pg/ml, respectively, in an air,”, flame using a 150-watt xenon arc lamp and a shielded HCDT, respectively. Omenetto and Rossi (%E) obtained a detection limit of 0.5 pg/ml for M g using an air,”? flame and a Hg line at 285.24 n m from a H g vapor discharge arc lamp. Rossi and Omenetto (41E) obtained a detection limit of 0.03 pg/ml using a similar flame and a water cooled HCDT. Bratzel, Dagnall, and Winefordner (7E) evaluated premixed and unpremixed air/HZ, Oz/H2, Ar/entrained air/H2, N,O/H?, and N20/C2H2 flames for 222
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atomic fluorescence of Mg. The influence of flame gas composition, height, and interferences on Mg fluorescence was investigated. The optimum flame types recommended were N20/H2 if negligible chemical interference was present and NzO/CZHZif appreciable chemical interference was present. Zacha et al. (61E) obtained detection limits of 0.02 and 0.03 pg/ml, respectively, for Ca in an air/Hz flame and Sr in an Ar/entrained air/Hz flame using EDT’s (prepared as iodides). Demers and Ellis (@E) also reported a detection limit of 0.02 pg/ml for Ca using an entrained air/Hz flame and a 450-watt xenon arc source. Similar interferences as in atomic absorption were found in atomic fluorescence by the latter authors. Manning and Heneage (%E) obtained a detection limit of 2.0 kg/ml for Ca in an air/Hz flame using a 150-watt xenon arc lamp. No detection limits have been reported for Ba during the past two years. Group IIIa Elements. T h e lines of the Group I I I a elements studied b y atomic fluorescence are: Ga, 403.3 and 417.2 n m ; I n , 410.5 and 451.1 n m ; and T1, 377.6 and 535.0 nm. T h e first lines listed for each element are resonance lines and the second are direct line fluoresence. Omenetto and Rossi (%E) studied the direct line fluorescence of Ga, In, and T1 in a n air/HZ flame using vapor discharge arc lamps. They measured the ratio of direct line to resonance fluorescence for each element and found it to be greatest for Ga and least but appreciable for T1. The direct line fluorescence was actually augmented by thermal excitation of these atoms to the metastable level involving the direct line fluorescence, and so in this case “direct line” fluorescence was actually thermally stimulated resonance fluorescence. The latter mechanism was not significant for T1 because of the large energy difference between the ground and metastable levels. Browner, Dagnall, and West (11E) obtained a detection limit of 0.12 pg/ml for TI using an air/Hz flame and an E D T (prepared as Tl(1) chloride). They studied the relative fluorescence intensities of the most sensitive T1 lines. Zacha et al. (51E) obtained detection limits of 1.0, 0.1, and 0.008 pg/ml for Ga in an air/Hz flame, I n in an Ar/ entrained air flame, and T1 in a n -4r/ entrained air flame using EDT’s (Ga and I n prepared as iodides; T1 prepared as metal). The value for T1 is similar to the best reported values obtained by flame emission and atomic absorption; the limits of Ga and I n are somewhat poorer than the best values reported by flame emission and atomic absorption. Bratzel, Dagnall, and Winefordner (YE) evahated premixed and unpre-
ANALYTICAL CHEMISTRY, VOL. 42, NO. 5 , APRIL 1976
mixed
air/Hn,
Ar/entrained
air,”,,
02/H~,NzO/HZ, and N20/C2H2 for Ga and T1 fluorescence. They studied the influence of flame type, height, and interferences upon the fluorescence of Ga and T1. The N20/H2 flame was recommended if solute vaporization interferences was small and the NzO/ CzHz if large. Bratzel, Dagnall, and Winefordner (6E) also studied the influence of organic and aqueous solvents, type of nebulizing gas, scattering of exciting light, and the effect of flame background upon the atomic fluorescence signals of Ga and TI when using premixed laminar and unpremixed turbulent Hz-supported flames. They recommended the use of the unpremixed air/Hz although all unpremixed and premixed Hz-supported flames gave similar results because of air entrainment. Dinnin ( M E ) obtained detection limits of 5, 50, and 0.1 pg/ml for Ga, In, and T1, respectively using an air/Hz flame and a hot H C D T . Dinnin and Helz (%E) described the construction of such sources. Manning and Heneage (%E) obtained detection limits of 0.5, 0.2, and 0.1 pg/ml for the same elements using an air/Hz flame and shielded HCDT’s. The same authors obtained values of 5,2, and 0.2 pg/ml for the same elements using a n air/Hz flame and a 150-watt xenon arc lamp. Rossi and Omenetto (41E) obtained detection limits of 1.0 and 0.1 pg/ml for Ga and T1, respectively, using a n air/Hz flame and demountable water cooled HCDT’s. Group IVa Elements. T h e lines of the Group IVa elements studied primarily b y atomic fluorescence are : Ge, 265.1 n m ; Sn, 303.4 n m ; P b , 283.3 and 405.8 n m and Si, 251.6 nm. Since the stability of the monoxides of Si, Ge, Sn, and Pb decreases rapidly with atomic weight, t h e fluorescence intensities for equal concentrations increase rapidly from Si to Pb. Silicon fluorescence has been reported by Dagnall et al. (133) using a silicon E D T (prepared from iodide; the ratio of Si to I was quite critical). A limit of detection in an Ar-sheathed separated fuel rich ?rT20/C2H2flame was 0.55 pg/ml. No interferences from a wide range of cations and anions were observed. Germanium has been examined by Dagnall, Thompson, and West (16E) using an Oz/S2/CzHz flame and an EDT (prepared from iodide). They also studied the relative fluorescence of several Ge lines. 4 detection limit of 15 pg/ml was reported. Bratzel, Dagnall, and Winefordner (6E) studied the influence of isopropanol-water mixtures, quenching of several nebulizing gases, the extent of scattering, and burner height on the fluorescence signal and signal-to-noise of Sn in premixed laminar and unpremixed
turbulent air/Hz and Ar/entrained air/ Hz flames produced using total consumption nebulizer burners. An E D T (prepared from iodide) was used in all studies. Best fluorescence intensities resulted when using Ar rather than O2 or Nz as the separating gas. Browner, Dagnall, and West (1OE) reported a detection limit of 0.1 pg/ml for Sn with a nitrogen-separated Ar/OZ/H2 flame and a modulated EDT source. A variety of flames, analytical lines, and interferences were studied for Sn fluorescence. These authors recommended the use of ac electronics and modulated sources for the elements of this group due to the presence of a rather high flame background. Lead fluorescence has been observed a t the resonance line (283.3 nm) and the direct-line fluorescence line (405.8 nm) b y several groups. Bratzel, Dagnall, and Winefordner (6E) investigated the effect of isopropanol-water mixtures, nebulizing gas type, scatter of exciting radiation, and flame height upon the fluorescence of P b in premixed laminar and unpremixed turbulent air,”? flames. The latter flame !vas recommended for atomic fluorescence studies when interferences were minimal. An E D T (prepared from the pure metal) was used. Zacha et al. (51E)obtained a detection limit of 0.5 pg/ml for P b using an Ar/entrained air/Hz flame and a n E D T (prepared from the metal). Smith, Stafford, and Winefordner (443)obtained a similar value in aqueous solutions but a much poorer value in methyl isobutyl ketone and in jet engine oils. Dinnin ( M E ) obtained a detection limit of 1.0 pg/ml for P b using a n air/H2 flame and a demountable hot H C D T . Rossi and Omenetto (41E)using a n air/ H2 flame and a demountable water cooled H C D T also obtained a limit of detection of 1.0 pg/ml. Manning and Heneage (S2E) were able to detect 3 and 1.0 pg/ml of P b using air/Hz flames and a 150-watt xenon arc lamp and a shielded H C D T , respectively. T h e same authors ( % E ) were able to detect 0.02 pg/nil using the same flame and a high intensity H C D T . This is one of the few cases where the high intensity HCDT’s give lower detection limits than the EDT’s. The 0.02 pg/ml value is similar to the best values reported for P b by atomic absorption and emission flame spectrometry. Group Va Elements. T h e lines of the Group Va elements primarily studied b y atomic fluorescence include: As, 189.0, 193.7, and 197.2 n m ; Sb, 231.2, 206.8, 217.6 a n d 259.8 n m ; a n d n i , 302.6 a n d 306.8 nm. Since these elements are easily atomized in flames, most studies have been carried out using cool air,”? flames. The most thorough studies of these elements have been performed by
Dagnall, Thompson, and West (2OE22E). They (2OE) studied the fluorescence spectrum of Sb in a n air/propane flame using a n E D T (prepared from iodide) and obtained a detection limit of 0.05 pg/ml. The same authors (21E) used a n iodine E D T with a line a t 206.163 nm to excite Bi in a cool Kz/entrained air/H* flame or a n &/entrained air/Hz flame. By exciting the Bi line a t 206.170 nm with the iodine line a t 206.163 nm, the direct line fluorescence a t 302.6 n m proved to be the most intense transition due to a deexcitation of Bi to a lower excited state following excitation. A detection limit of 0.05 pg/ml was obtained. The intense fluorescence line a t 306.8 nm was not as useful because of the presence of intense O H band emission from the flame gases. Several other Bi fluorescence lines were also observed. The same authors (22E) used an E D T (prepared from iodide) and cool N2/entrained air/H2 or dr/entrained air/H2 diffusion flames as well as premixed flames to excite As and obtained a detection limit of 0.2 pg/ml. The limits of detection for Sb, Bi, and As by atomic fluorescence compare favorably with the best values reported for other flame methods. For the three elements in Group Va, the above authors (2OE-22E) performed a thorough interference study and found no interferences even with 100-fold excesses of many cations and anions. Dagnall and West (2SE) and Dagnall, Thompson, and West (17E) reviewed the preparation and spectral characteristics of EDT’s for Sb, Bi, and As and the production of atomic fluorescence using these lamps and a variety of cool flames, including Ar/entrained air/H2, Xz/entrained air/H2 and air/ C2H2. Menis and Rains ( N E ) also prepared an E D T for As using the Dagnall and West (2SE) procedure. Zacha et al. (51E) obtained detection limits of 0.4 and 0.7 pg/ml for Sb and Bi (using the 306.8 nm resonance line) in air/H* and Ar/entrained air/Hs turbulent diffusion flames, respectively. The sources used for these studies were EDT’s (prepared as iodides), Dinnin (25E) obtained a detection limit of 0.1 pg/ml for Bi using an air/H2 flame and a demountable hot HCDT. Manning and Heneage (S1E) obtained for As a detection limit of 1.0 pg/ml using a high intensity H C D T and an air/H2 flame. The same authors (S2E) could detect only 200 and 300 pg/ml of Bi and Sb, respectively, using an air/H2 flame and a 150-watt xenon arc lamp. The detection limits were 10 and 20 pg/ml for the same elements in the same flame using shielded HCDT’s. Group VIa Elements. T h e lines of the Group VIa elements studied primarily in atomic fluorescence spectrometry have been: Se, 196.1, 204.0, 206.3, and 214.3 n m ; and Te, 238.3
a n d 238.6 nm. The most ext’ensive analytical studies on these elements has once again been performed b y Dagiiall, Thompson, and West (18E, 19E). The details of preparing EDT’s (Se-pure metal and Te-as iodide) were described in the first article (18E) and the relative fluorescence intensities of various Se and T e lines was given in the latter article (19E). The excitation process may involve resonance absorption from the ground state and resonance or direct-line fluorescence or thermal excitation to a low lying metastable state and excitation followed by resonance fluorescence. I n the latter paper (19E),detection limits of 0.25 and 0.12 pg/ml, respectively, for Se arid T e using EDT’s and an air/propane flame were reported. S o appreciable interferences for a wide range of cations and anions were found. Dagnall and West, (2SE) and Dagnall, Thompson, and West (17E) reviewed the preparation and characteristics of EDT’s of Se and T e and the production of atomic fluorescence using an air/propane flame. The above detection limits are comparable to the best values reported by other flame methods. Zacha et al. (61E) obtained detection limits of 0.4 and 0.5 pg/ml for Se and T e using a turbulent Ar/entrained air/ H2 flame and EDT’s (prepared from pure metal). Group I b Elements. The lines of the Group I b elements studied in atomic fluorescence include: C u , 324.8 and 327.4 n m ; Ag, 328.1 and 338.3 nni; and Xu, 267.6 nm. T h e lowest limit of detection yet reported for Cu was 0,001 pg/ml by Manning and Heneage (S1E) using an air/Hs flame and a high intensity H C D T . This value is below the best values reported in atomic absorption and flame emission spectrometry. Smith, Elser, and Winefordner(42E) using a similar source and an .$r/entrained air/Hg flame obtained a detection limit of 0.003 g / m l and a linear analytical curve covering five decades of concentration. I n the presence of 0.01X HCl, only aluminum, phosphate, and silicate gave chemical interferences. These latter authors also showed that in favorable instances, nearly 1% total dissolved solids did not cause significant scattering of exciting light in low temperature Hs-supported flames. Zacha, et al. (51E) obtained a detection limit of 0.005 pg/ml for Cu in an Xr/entrained air/Hz flame using an E D T (prepared as iodide). Smith, Stafford, and Winefordner (44E) obtained similar results in aqueous solutions but about 10-fold poorer in methyl isobutyl ketone and in jet engine oils. Dinnin (25E) was also able to detect 0.001 pg/ml of Cu in an air/H2 flame using a hot H C D T . LIaIining and Heneage (S2E) mere able to detect
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only 0.01 pg/ml using a shielded H C D T and the same air/H2 flame used for the high intensity H C D T (S1E). Omenetto and Rossi (%E) using the continuum from a Hg vapor discharge arc lamp and an air/H2 flame detected 0.1 pg/ml of Cu. Rossi and Omenetto (41E)using a demountable water-cooled H C D T also detected 0.1 pg/ml. The best detection limit so far for Ag was the 0,0001 pg/ml value obtained by Zacha et al. (51E) using an air/H2 flame and an EDT (prepared as iodide). Smith, Stafford, and Winefordner (44E) obtained a 10-fold poorer value using similar condit,ions and even worse when using nonaqueous solvents and jet engine oils. Aldous, Dagnall, and West (SE) described the preparation and spectral characteristics of Ag and Xu EDT’s (prepared as iodide or chloride for Ag and iodide for Au) but gave no analytical results. West and Williams (48E) using an oxidizing air/propane flame (better than X20/C2H2flame) and a high intensity H C D T obtained a detection limit of 0.002 pg/ml for Xg. The relative intensities of a number of Ag fluorescence lines, the influence of flame type, the effects of size of primary and secondary currents, and the magnitude of interferences were also studied. The same interferences as in atomic absorption were found. Manning aiid Heneage (S2E) were able to detect 0.2 and 0.003 pg/ml Ag using an air/H2 flame and a 150-watt xenon arc lamp and a shielded H C D T , respectively. Rossi aiid Omenetto (41E) using a demount’able H C D T and an air/H2 flame detected 0.03 pg/ml Ag. Dinnin (26E) obtained a detection limit of 0.001 pg/ml Ag using a hot H C D T and an air/Hz flame. Gold fluorescence has been observed by Zacha et al. (51E), Manning and Heneage (SWE), and Dinnin (26E). The first group obt’ained a detection limit of 0.2 pg/ml Au in an air/Hn flame using an E D T (prepared as iodide). The second group detected 10 pg/ml Xu in an air/H* flame using either a 150watt, xenon arc lamp or a shielded HCDT. The third aut’hor detected 4 pg/ml using a hot, H C D T and an air/H2 flame. These values are inferior to those in atomic absorption. Group IIb Elements. T h e only lines studied in atomic fluorescence spectrometry for Group I I b have been: Zn, 213.9 n m resonance line; Cd, 228.8 n m resonance line; and Hg, 253.7 n m intercombination line (the Hg, 184.9 n m resonance line is in a spectral region in which atmosphere absorpt,ion is appreciable). If heaven exists for atomic fluorescence, this Group is it’ as can be noted by the spectacular limits of detection obtained by many workers. Most det,ection limits are considerably
better than by other flame methods. For example, Zacha et al. (51E)gave detection limits of 0.00004, 0.000001, and 0.1 pg/ml for Zn, Cd, and H g in an air/Hz flame using EDT’s (prepared as metals for all three). Manning and Heneage (S2E) obtained limits of detection of 20 and 2 pg/ml for Zn and Cd, respectively, using an air/H2 flame and a 150-watt xenon arc lamp. The same authors using the same flame but shielded HCDT’s obtained detection limits of 0.05 and 0.5 pg/ml, respectively, for Zn and Cd. Omenetto and Rossi (%E) obtained detection limits of 0.0005 and 0.005 pg/ml for Zn and Cd, respectively, using an air/H2 flame and metal vapor discharge arc lamps. Vickers and Merrick (46E) detected 0.002 pg/ml of H g using an extraction method, an O Z / H ~ flame, and a Hg-pen light (no values in aqueous solution were reported). Bratzel, Dagnall, and Winefordner (6E)compared various premixed laminar and unpremixed turbulent flames for Cd fluorescence. The influence of organic solvents, type of nebulizing gas, scatter of incident light, and flame height upon Cd fluorescence signals and signal-to-noise ratios were studied for both types of flames. Bratzel, Dagnall, and Winefordner (YE)studied Cd fluorescence in premixed and unpremixed air/ H2, Ar/entrained air/H2, N20/H2 and premixed N20/C2H2flames produced using a total consumption nebulizer burner. The premixed and unpremixed H2 supported flames gave similar fluorescence signals and interferences with Cd and were preferred over other flames if chemical interferences were negligible. If chemical interferences were appreciable, then the IL’2O/C2H2 flame was preferred. Browner, Dagnall, and West (11E) compared atomic fluorescence with atomic absorption flame spectrometry for Hg when using EDT’s (prepared from metal) and a lean air/H2 flame. They obtained a detection limit of 0.12 pg/ml which was about 10-fold below the absorption value. These authors also found that ascorbic acid had to be added to all solutions to obtain reliable results. Hobbs et al. (29E) used a K2 separated air/C2H2 flame and metal vapor arc discharge lamps for producing atomic fluorescence of Zn (0.0002 pg/ ml detection limit) and of Cd (0.0005 pg/ml detection limit). Bratzel and Winefordner (8E) investigated the influence of acid type and concentration upon Cd fluorescence. Group IIIb-VIIIb Elements. Atomic fluorescence has been observed from most of the first row transition elements and several of the second and third row as well. The most extensive study of the atomic fluorescence characteristics of Fe, Co, and Ni has been carried out by Matousek
224R * ANALYTICAL CHEMISTRY, VOL. 42, NO. 5 , APRIL 1970
and Sychra (%E). They studied the relative fluorescence intensities of various lines, the shapes of analytical curves, and the limits of detection of these elements. The strongest fluorescence occurred for Fe, Co, and Ni a t 248.3, 240.7, and 232.0 nm, re9pectively. The limits of detection of Fe, Co, and Ni in premixed Ar/02/H2 and unpremixed air/Hz and Ar/02/H2 were 0.02, 0.01, and 0.003 pglrnl, respectively. By use of an extraction method, the detection limits were lowered by about 100-fold. Fleet, Liberty, and West (27E) obtained fluorescence from Co in premixed air,”*, air/propane, and air/ CzH2 flames using a high intensity H C D T and an E D T (prepared as iodide). The latter source and either air/H2 or air/propane flames resulted in a limit of detection of 0.005 ,ug/ml. Manning and Heneage (32E) obtained limits of detection of 1, 2, 3, 0.5, 10, 50, 10, 500, 100, and 100 pg/ml for Fe, Co, Si, Mn, Cr, Pd, Rh, P t , Ru, and Ir, respectively, in an air,”* flame using a 150-watt xenon arc lamp. The same authors using the same flame and shielded HCDT’s obtained limits of detection of 0.4, 0.2, 0.1, 0.05, 20, 2, 3, 50,200, and greater than 1000 pg/ml for the same elements. Using high intensity HCDT’s, the same authors ( S I E ) obtained detection limits of 0.1, 0.04, and 0.003 pg/ml for Fe, Co, and Ni, respectively, in an air/H2 flame. Zacha et al. (51E) obtained detection limits of 0.2, 0.1, 0.04, 0.006, and 10 pg/ml for Fe, Co, Xi, N n , and Cr, respectively, in an air/H2 or Xr/entrained air/H2 flame using EDT’s (prepared as iodides). Smith, Stafford, and Winefordner (&E) using the same type sources and an Ar/entrained air/ Hz flame had detection limits of 1 pg/ml for both F e and Ni. Bratzel, Dagnall, and Winefordner (6E) studied the influence of organic solvents, nebulizing gas type, flame height, and scatter of exciting light upon the fluorescence signal and signal-to-noise ratio of Fe in premixed laminar andunpremixed turbulent air/Hs flames. Bratzel, Dagnall, and Winefordner (YE) also compared premixed and unpremixed air/Hz, Arlentrained air/H2, 02/Hzand N 2 0 / H 2 and premixed N20/C2H2 flames produced using total consumption nebulizer burners. Maximum fluorescence of Fe occurred a t low flame heights. Because of the large amount of air entrainment in all unsheathed unpremixed and premixed Hz supported flames (4SE), the enhancement of quantum efficiency by use of Ar is rather small. Thus the main concern with such flames was to improve limits of detection via improvement in atomization efficiency and minimization of interferences. Easily vaporized elements, such as Cd, Zn, Se, Te, Sb, Bi, As, etc., should be de-
termined above the luminous part of the flame background, whereas more difficult to vaporize elements, e.g., F e and Mg, must be measured within the flame gases. Dinnin (Z5E) obtained detection limits of 5, 0.5, 0.1, 5, and 100 Mg/ml for Fe, Co, Xi, M n and Cr, respectively, in an air/Hz flame using hot HCDT’s. There is some question concerning the validity of the limits of detection for Pd, Pt, Al, Zr, and T i reported by Dinnin (Z5E). There is also some question concerning the validity of the values for Be, Hf, Sc, Ti, U, and Zr reported by Zacha et al. ( 5 f E ) . The observed “fluorescence” signals for these two groups seemed to be a result of scattering of exciting light for these elements. Rossi and Omenetto ( 4 f E ) using a demountable water cooled H C D T and an air/Hz flame reported detection limits of 2, 0.3, 1, 0.05, and 1 for Fe, Co, Xi, Mn, and Cr, respectively. The same authors (38E) using the same flame and a Hg vapor discharge lamp source had detection limits of 1, 3, 0.5, 5, and 10 pg/ml for Fe, Ni, Mn, Cr, and Pd, respectively. The 248.27 nm Hg line was used to excite Fe a t 248.33 nm; the Ni 232.0 nm line was excited by the continuum of the Hg source; the hfn 279.482 nm line was excited by the Hg source continuum; Cr 359.349 nm line was excited by the 359.348 Hg line; and the Pd 340.458 nm line was excited by the 340.365 Cd line. Rossi and Omenetto ( 4 f E ) using water cooled HCDT’s and an air/Hz flame had detection limits of 2, 0.3, 1, 0.05, and 1 pg/ml for Fe, Co, Ni, Mn, and Cr, respectively. Aldous, Dagnall, and West ( S E ) described the preparation of P t and P d EDT’s. All lamps (including those of Ag and Au) were prepared from the element and chlorine. The spectral characteristics of the resulting lamps were reported. Dagnall, Pribil, and West ( f 4 E ) and Zacha et al. ( 5 f E ) described the preparation of EDT’s for Ti, V, and Zr. Spectral characteristics of the lamps were given. No limits of detection of any of these elements in atomic fluorescence were reported. The studies performed up to the present time indicate the need for a thorough investigation of the fluorescence of the transition elements. It certainly seems apparent that high temperature, low burning velocity flames, such as NzO/ CZHZ, will be necessary to obtain efficient atomization. Also the EDT’s prepared using the chlorides rather than the iodides seem necessary. The Lanthanides. X o documented atomic fluorescence flame spectrometric studies of the lanthanides (elements 58-71) have been reported during the past two years. The Actinides. KO real evidence
of atomic fluorescence of the actinides (elements 90-103) has been reported during the past two years. Other Studies. Several studies of interest to flame spectroscopists do not belong in any of the above categories b u t still should be listed. Flame Cells. Bratzel, Dagnall, and Winefordner (7E) described the use of premixed flames produced using a total consumption nebulizer burner. The gases (HZor CZHZfuels and Oz, Ar, air, or NzO oxidants or diluents) were premixed in small chambers prior to introduction into the “fuel” and oxidant ports. The flames produced were quite laminar as noted from Shadowgram and temperature profiles. The flame system used was previously described by Mossotti and Duggan ($723). Nonflame Cells. Nassmann (34E) used a heated graphite cell instead of a flame cell for both atomic fluorescence and atomic absorption studies. T h e samples were vaporized using electrical resistance heating of t h e cell in a n Ar atmosphere. For the determination of Zn and Cd, atomic fluorescence resulted in absolute detection limits of 4 X l O - l 4 and 2.5 X g, respectively, and atomic absorption gave poorer results of about 8X and 2 X g for the same elements. The absolute detection limits for Sb, Fe, T1, Pb, Mg, and Cu by atomic fluorescence were 2 X 3 x 10-9,2 x 10-9,3.5 x io-11,3.5 x and 4.5 X g, respectively; the results by atomic absorption were slightly better because of the lack of intense line sources for atomic fluorescence. Massmann used laboratory constructed high intensity HCDT’s. N o matrix effects were found in the atomic fluorescence studies as long as the transient signals were integrated. West and Williams (50E) described a carbon filament atom reservoir for atomic fluorescence and atomic absorption studies. Aqueous solutions (5 11) were placed upon the filament and vaporized into an Ar atmosphere oia electrical resistance heating. Analyses were completed in 5 seconds, and limits of detection of 3 x 10-11 g and g for Ag a t 328.07 nm and Mg a t 285.21 nm, respectively, were obtained. High intensity HCDT’s were used. Other Source Studies. A1 Ani, Dagnall, and West (1 E ) described the preparation of a longer lived Cu E D T . The lamp was prepared from copper(1) chloride and mercury and was intense, stable, and long-lived if run a t less than 50 watts. The most extensive single investigation of the preparation, operation, and characteristics of EDT’s has been given by Mansfield et al. (3%). These authors used a statistical evaluation of data to obtain the optimum lamp geometry, type of material to be excited,
gas pressure, and microwave coupling devices. Limits of detection in atomic fluorescence flame spectrometry were listed for sixteen elements-Ag, Au, Bi, Cd, Co, Cu, Ga, Hg, In, Mg, Mn, Pb, Se, Te, T1, Zn. Browner, Dagnall, and West (QE) described electronic modulation of EDT’s by superimposing a 50-Hz component upon the dc potential of the anode of the magnetron. Modulated EDT’s gave greater atomic absorption sensitivity for P b and Sn than HCDT’s. Dagnall, Taylor, and West (15E) reviewed the construction and operation of EDT’s for 21 elements-Ag, Al, As, Bi, Cd, Co, Cr, Cu, Fe, Ga, Hg, In, Mn, Ni, Pb, Sb, Se, Sn, Te, Tb, and Zn. Atomic fluorescence limits of detection were 10-fold lower than the corresponding atomic absorption values. Aldous et al (ZE) have described EDT’s containing organo-sulfur and organo phosphorous compounds. When operated a t microwave frequencies, the S lamp contained CS, SZ, CN, and Nz emission bands and the P lamp contained CO, CN, Nz, and PO emission bands. Both lamps emitted the atomic carbon line. These lamps were studied only to evaluate the emission spectra of organo compounds excited within a microwave excited gas chromatographic detector. Bailey (5E) described the basis of selecting excitation and fluorescence lines in atomic fluorescence spectrometry. Good agreement between calculated and experimental results were obtained for Ag, Co, and Fe but not for Ni. Solar Blind Detectors. Larkins et al. (30E) described the use of solarblind detectors in flame spectrometry. Such detectors have virtually no response below 310 nm. The authors recommended the use of these detectors for selective modulation techniques, resonance detectors, and atomic fluorescence techniques, especially multielement analysis. The authors postulated the development of a simple flame fluorescence instrument for simultaneous multielement analysis using solar-blind detectors in conjunction with several lamps operated at different frequencies. Synchronous demodulation would be used to isolate the desired signals. A novel use of a solar-blind multiplier phototube was put forth by Vickers and Vaught (47E) who developed a simple nondispersive atomic fluorescence instrument. The instrument consisted of metal vapor arc lamps for Cd and Zn or a pen light for Hg, a flame atomizer, and a solar-blind detector. No spectral isolation devices were needed as long as the flame background and light scattering were minimal. They obtained detection limits of 0.001, 0.0002, and 1 Mg/ml for Cd, Zn, and Hg, respec-
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tively, using the simple, inexpensive device. This system should also work well with As, Sb, Ri, Se, and T1. Applications. Unfortunately few applications of atomic fluorescence flame spectrometry appeared during the past two years. Smith, Stafford, and Winefordner (443) evaluated atomic fluorescence flame spectrometry for the determination of wear metals in jet engine lubricating oils. The authors obtained results on Ag, Cu, Fe, and M g in jet engine oils using a total consumption nebulizer burner with a n air/Hz flame or an hr/entrained air/Hz flame and EDT’s. The results compared favorably with atomic absorption and the rotating disk-spark method. No pretreatment of the oils were needed prior to nebulization directly into the flame. Atomic fluorescence was recommended for the determination of Ag, Cu, Fe, Mg, I%, and P b using the above conditions. Elements, such as Al, Cr, Sn, and T i could not be measured using the cool HPsupported flames. Sychra, Matousek, and Masek (45E) found atomic fluorescence to be more sensitive than atomic absorption flame spectrometry for N i in petroleum fractions. They used a high intensity H C D T to determine concentrations as low as 0.01 Gg/ml of Ni in n-heptane and xylene of petroleum fractions. Demers and Ellis (ZCE) also indicated that atomic fluorescence flame spectrometry should be useful for trace analysis. LITERATURE CITED Reviews, Books, and Bibliographies
(1A) Alkemade, C. T. J., Appl. Opt., 7, 1261 (1968). (2A) American Society for Testing and Materials, “Atomic Absorption Spectroscopy,” 443, ASTM, Philadelphia, Pa., 1969. (3A) Angino, E. E., Billings, G. K., “Atomic ,,Absorption Spectrometry in Geology, American Elsevier, New York, 1967. (4A) Baer, W. K., Perkins, A. J., Grove, G. L., Eds., “Developments in A p plied Spectroscopy,” Plenum Press, New York, 1969. (5A) Baker, R. A., “Trace Inorganics in Water,” Advances in Chemistry Series, No. 73, American Chemical Society, Washington, D. C., 1968. (6A) Beamish, F. E., Lewis, T. L., Van Loon, J. C., Talunta, 16, 1 (1969). (7A) Boettner, E..A., Grunder, F. I., in “Trace Inoreanics in Water.” R. A. Baker, Advalces in Chemistiy Series, No. 73, ACS, Washington, D. C., 1968. (8A) Bradenberger, Von. H., Chimia, 22, 449 (1968). (9A) Brech, F., J . Ass. Ofic. Anal. Chem., 51, 132 (1968). (10A) Dawson, J. B., Heaton, F. W., “Spectrochemical Anal sis of Clinical Material,” Charles C Jhomas, Springfield, Ill., 1967. (11A) Dean, J. A,, Rains, T. C., “Flame Emission and Atomic Absorption Spectrometry,” Vol. 1, Dekker, New York, N. Y., 1969. (12A) DeGalan. L.. Chem. Weekbl.. 64 ’ (29), 11 (1968). ’ 226R
(13A) Demers, D. R., Appl. Spectrosc., 22, 797 (1968). (14A) Ellis, D. W., Demers, D; R., in “Trace Inorganics in Water, R. A. Baker, Advances in Chemistry Series, No. 73, Washington, D. C., 1968, p 326. (l5A) Elwell, W. T., Gidley, J. A. F., “Atomic Absorption Spectrophotometry, 2nd Ed., Pergamon Press, New York, N. Y., 1966. (16A) Erdey, L., Zh. Anal. Khim., 24, 48 (1969). (17A) Evans Electroselenium, Ltd., “Atomic Absorption Analytical Methods,” Vol. 1, Halstead, Essex, England, 1967. (18A) Fisher Scientific Co., “Bibliography for Atomic Absorption Spectroscopy, Pittsburgh, Pa., 1968. (19A) Golterman, H. L., Clyne, R. S., “Methods for Chemical Analysis of Fresh Water,” F. A. Davis Co., Philadelphia, Pa., 1969. (20A) Grant, C. L., in “Atomic Absorp tion Spectroscopy,” Am. SOC.Testing Mater., S.T.P. 443, Philadelphia, Pa., 1969, p 37. (21A) Grove. E. L.. Perkins. A. J.. “Developments in Applied Spectrosbopy,” Vol. 7A, Plenum Press, New York, N. Y . .1969. ~ - - I
(22A) -Herrmann, R., Zeiss Infomation, 68,62 (1969). (23A) Kahn, H. L., in “Trace Inorganics in Water,” R. A. Baker, Advances in Chemistry Series, No. 73, American Chemical Society, Washington, D. C., 1968. ~- -,D. 183. (24A) Kirkbright, G. F., Lab. Practice, 17, 906.(ivaa). (25A) Koirtyohann, S. , R., in “Develop ment,s in Applied Splectroscopy,” Baer, W. K., Perkins, A. J., Grove, E. L., Eds.. Vol. 6. Plenum. Press, New York, N. Y . , 1968,‘p 67. (26A) Lermond, C. A., Capacho-Delgado, L., “Atomic Absorption Bibliography,” Bausch and Lomb, Inc., Rochester, N . Y., 1968. (27A) Lems, L. L., 4NAL. CHEM., 40, (12), 28A (1968). (28A) Lewis, L. L., in “Atomic Absorp tion Spectroscopy,” Am. SOC.Testing Mater., S.T.P. 443, Philadelphia, Pa., 1969., D 47. ~(29A)-L’Vo;, B. V., “Atomic Absorption Analysis, Nanlla, MOSCOW,USSR, 1966. (30A) Margoshes, M., Scribner, B. F., ANAL.CHEM.,40, (5), 223R (1968). (31A) ?$am, G. V., “Plasma Spectroscopy, American Elsevier, New York, N. Y., 1969. (32A) Martin, D. F., “Marine Chemistry: Analytical Methods,” Vol. 1, Dekker, New York, N. Y., 1968. (33A) Masek P. R., Sutherland, I., “Atomic Absorption and Flame Emission Abstracts,” Science and Technology Agency, London, 1969. (348) Massmann, H., Chimia, 21, 217 (1967). (35A) Perkin-Elmer Corp., “Analytical Methods for AAomic Absor tion Spectrophotometry, Norwalk, 8onn., 1968. (36A) Piccolo, B., O’Connor, R. T., J . Amer. Oil Chem. SOC.,45, 789 (1968). (378) Pickett, E. E., Koirtyohann, S. R., ANAL.CHEM.4 1 (14), 28A (1969). (38A) Price, W. J., “Atomic Absorption Spectroscopy” (chapter in “Spectroscopy,” Browning, D. R., Ed.), McGraw-Hill Book Co., Inc., New York, N. Y., 1969. (39A) Price, W. J., “Atomic Fluorescence Spectroscopy” (chapter in “SpectroscopyI1’ Browning, D. R., Ed.), McGraw-Hill Book Co., Inc., New York, N. Y., 1969. 1
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(40A) “Proceedings of the XI11 Colloquium Spectroscopicum Internationale,” Hilger, London, 1967. (41A) “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967. (42A) Pungor, E., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, D 369. (43A) Rains, T. C., in “Atomic Absorp tion Spectroscopy,” Am. SOC.Testing Mater., S.T.P. 443, Philadelphia, Pa., 1969, p 19. (44A) Ramirez-Munoz. J.. “Atomic Absorption Spectroscopy and Analysis bX Atomic Absorption Flame Photometry, American Elsevier Publishing Co., Inc., New York, N. Y., 1968. (45A) Reiss, R., “Atomic Fluorescence Bibliography,” Aztec Instruments, Inc., South Norwalk, Conn., 1969. (46A) Ringhardtz, I., Welz, B., 2. Anal. Chem., 243, 190 (1969). (47A) Robinson, J. W., “Atomic Absorp tion Spectroscopy,” Dekker, New York, N . Y., 1966. (48A) Robinson, J. W., Spectrosc. Lett., 2, 37 (1969). (49A) Rubeska, I., Moldan, B., ::Atomic Absorption Spectrophotometr Chemical Rubber Co., Cleveland, (%io, 1969. (50A) Slavin, W., At. Absorption Newslett., 7, 1 (1968). (51A) Slavin, S., At. Absorption Newslett., 8 , 8 (1969). (52A) Slavin, W., “Atomic Absorption S ectroscopy,” Interscience, New York, Y.. 1968. (53A) Siavin, W., Slavin, S., Appl. Spectrosc., 23, 421 (1969). (54A) Vallee, B. L., Clin. Chim. Acta, 25, 307 (1969). (55A) Walsh, A., in “Atomic Absorp tion Spectroscopy,” Am. SOC.Testing Mater., S.T.P. 443, Philadelphia, Pa., 1969. D 3. (56A) Warn, J. R. W., Meas. Znstr. Rev., 15, 505 (1968). (57A) Ibid., p 576. (58A) Zbid., p 669. (59A) West, T. S., Minerals Sci. Engany I (a), 3 (1968). (60A) Winefordner. J. D.. Rec. Chem. Proor.. 29. 1 (1968). (GlA)“Winejordner,-’ J. D., Mansfield, J. M. Appl. Spectros. Rev., 1, 1 (1967). (62A) deegers, P. J. T., Smith, R., Winefordner, J. D., ANAL. CHEM.,40 (13), 26A (1968). ~
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Fundamental Studies
(1B) Alfano, R. R., Appl. Opt., 8, 2095 (1969).
(2B-?zkemade, C. T. J., Appl. Opt., 7, 1261 (1969). (3B) Anderson, R. C., J . Chem. Educ., 44,248 (1967). (4B) Artem’ev, V. V., Opt. Spektrosk., 23, 635 (1967).
1969. (9B) Baker, D. J., Steed, A. J., Appl. Opt., 7, 2190 (1968). (10B) Baranov, S. V., Mashtakov, L. K., Pofralidi, L. G., Zh. Prikl. Spektrosk., 10, 595 (1969). (11B) Barna, A., Cisneros, E. L., Rev. Sci. Instrum., 40, 370 (1969).
(12B) Barney, J. E., Talanta, 14, 1363 (1967).
(57B) Hobbs, R. S., Kirkbright, G. F., Sargent, M., West, T. S., ibid., p 997. (58B) Hobbs, R. S., Kirkbright, G. F., West, T. S., Analyst, 94 554 (1969). (59B) Hollander, T. J., hroida, H. P., Combust. Flame, 13, 63 (1969). (60B) Homann, K. H., Angew. Chem., 7, 414 (1968). (61B) Hooymayers, H. P., Spectrochim. Acta, 23B, 567 (1968). (62B) Hooma ers, H. P., Lijnse, P. L., J . Quunt. i!&ectrosc. Radiat. Transfer. “
I
9, 965 (igsgj. (63B) Hooymayers, H. P., Nienhius, G., ibid., 8, 955 (1968). (64B) Janin, J., ROW, F., D’Incan, J., Spectrochim. Acta, 23A, 2939 (1967). (65B) Jansson, R. H., Kolb, C. L., J. Quant. Spectrosc. Radiat. Transfer, 8 ,
(34Bj Dagnall, R. &I., Thompson, K. C., West, T. S., Analyst, 92, 506 (1967). (35B) Ibid., 93, 72 (1968). (36B) Zbid., p 153. (37B) Ibid., p 568. (38B) Ibid., 94, 643 (1969). (39B) De Galan. L.. Smith. R.. Winefordner, J. D.,‘ Spkctrochim’. A&, 23B, ,521 (1968). (40B) De Galan, L., Winefordner, J. D., i._ h .d . , p 277. (41B) Dixon-Lewis, G., Proc. Roy. SOC., 2988, 495 (1967). (4213) Zbid., 307A, 111 (1968). (43B) Dixon-Lewis. G.. Isles. G. L.. ibid.. ~
(44B) Eather, R. ’H., Reasoner, D. L., A p p l . Opt., 8, 227 (1969). (45B) Foord, R., Jones, R., Oliver, C. J., Pike, E. R., A p p l . Opt., 8 , 1975 (1969). (46B) Foskett, C. T., Weinberg, J. M., ibid., p 2185. (47B) ’Franklin, hf. L., Horlick, G., Malmstadt, H. V., ANAL.CHEM.,41, 2 (1969). (48B) Gilmore, F. R., Bauer, E., McGowan, J. W., J . Quant. Spectrosc. Radiat. Transfer, 9, 157 (1969). (49B) Gofmeister, V. P., Kagan, Y. >I., Opt. Spektrosk., 26, 689 (1969). (50B) Golden, S. A., J . Quant. Spectrosc. Radiat. Transfer, 7, 225 (1967). (5lB) Grimm, W., Spectrochim. Acta, 23B, 443 (1968). (52B) Halls, D. J., Pungor, E., Anal. Chim. Acta, 44, 40 (1969). (53B) Harrison, W. W., Juliano, P. O., ANAL.CHEM.,41, 1016 (1969). ( S B ) Hayhurst, A. N., Sugden, T. M., Trans. Faraday SOC.,63, 1375 (1967). (55B) Hieftje, G. M.,Malmstadt, H. V., ANAL. CHEM., 40, 1861 (1968). (56B) Hingle, D . N., Kirkbright, G. F., West, T. S., Talanta, 15, 199 (1968).
1399 (1968). (66B) Jenkins, D. R., Proc. Roy. SOC., 303A, 453 (1968). (67B) Zbid., p 467. (68B) Ibid., 306A, 413 (1968). (69B) Jenkins, D. R., Spectrochim. Acta, 23B, 167 (1967). (70B) Jenkins, D. R., Trans. Faraday Soc., 64,36 (1968). (71B) Jensen, D. E., ibid., 65,2123 (1969). (72B) Jessen, P. F., Gaydon, A. G., Combust. Flame, 11, 11 (1967). (73B) Katskov, D. A., Lebedev, G. C., L’vov, B. V., Zh. Prikl. Spektrosk, 10, 215 (1969). (74B) Kelly, R., Padley, P. J., Trans. Faraday SOC.,65,355 (1969). (75B) Zbid., p 367. (76B) Kennedy, E. J., DeLorenzo, J. T., Brashear, H. R., Rev. Sci. Znstrum., 40,1504 (1969). (77B) Kirkbright, G. F., Peters, M. K., Sargent, M., West, T. S., Talanta, 15, 663 (1968). (78B) Kirkbright, G. F., Sargent, M., West, T. S., ibid., 16, 245 (1969). (79B) Kirkbright, G. F., Semb, A., West, T. S., zbid., 14, 1011 (1967). (80B) Zbzd., 15,441 (1968). (81B) Kirkbright, G. F., West, T. S., A p p l . Opt., 7, 1305 (1968). (82B) Klein, L., ibid., p 677. (83B) Koirtyohann, S. R., Pickett, E. E., “XI11 Colloq. SpectroscoJjicum Internationale, Ottawa (1967), Adam Hilger, Ltd., London, 1968. (84B) Kostewski, J., Jasny, J., Grabowski, Z. R., A p p l . Opt., 7, 2178 (1968). (85B) Krawec, R., Rev. Sci. Znstrum., 39, 4021 (1968). (86B) Kruegle, H. A., Dolin, S. A., A p p l . Opt., 8, 2107 (1969). (87B) Larkins, P. L., Lowe, R. M., Sullivan, J. V., Walsh, A., Spectrochim. Acta, 24B, 187 (1969). (88B) Lavoie, L., Winston, R., Rev. Sci. Znstrum., 40, 1350 (1969). (89B) Lebedev, V. I., Dolidze, L. D., Talk given at Atomic Absorption Spectroscopy Conference, Sheffield, England, July 1969. (90B) Lowe, R. M., Spectrochim. Acta, 24B, 191 (1969). (91B) McEwan, M. T., Philips, L. F., Combust. Flame, 11, 63 (1967). (92B) McGillis, D. A., Krause, L., Can. J . Phvs., 46, 25 (1968). (93B) KIansell, R. E., A p p l . Spectrosc., 22, 790 (1968). (94B) Mansfield, J. M., Bratzel, M. P., Norgordon, H. O., Knapp, D. O., Zacha, K. E., Winefordner, J. D., Spectrochim Acta, 23B, 389 (1968). (95B) Mayden, D., Shaman, M., Rev. Sci. Instr.. 40. 218 (1969). (96B) Morton, ’G. A:, Appl. Opt., 7, 1 (1968). (97B) Mossotti, V. G., Duggan, M., ibid., p 1325
(98B) Mustafin, K. S., Seleznev, V. A., Shtyrkov, E. I., Opt. Spectrosc., 22, 174 (1967). (99B) Nicol, D. R., Rev. Sci. Znstrum., 40, 1300 (1969). (100B) O’Haver, T. C., Winefordner, J. D., A p p l . Opt., 7, 1647 (1968). (101B) O’Haver, T. C., Winefordner, J. D., J . Chem. Educ. 46, 241 (1969). (102B) Ibid.. D 435. (l03B) Orren, M. J., Chem. Processing, 3 (21, 35 (1968). (104B) Palmer, H. B., Combust. Flume, 11, 120 (1967). (105B) Pao, Y., Griffiths, J. E., J . C’hem. Phys., 46, 1671 (1967). (106B) Parlange, J. Y., J . Chem. Phys., 48, 1843 (1968). (107B) Parsons, M. L., J . Chem. Educ., 46. 290 (1969). - -, (l08b) Parsons, M. L., Winefordner, J. D., A p p l . Spectrosc., 21, 368 (1967). (109B) Pearce, S. J., DeGalan, L., Winefordner, J. D., Spectrochim. Acta, 23B, 793 (1968). (llOB) Pechorin, V. P., L’vov, B. V., Z h . Prikl Spektrosk., 7, 764 (1968). (111B) Pimentel, G. C., A p p l . Opt., 7, 2155 (1968). (112B) Pleskach, L. I., Rykov, N. A., 2. Anal. Khim., 24, 250 (1969). (113B) Prugger, H., Spectrochim. Acta, 24B, 197 (1969). (114B) Prugger, H. J., Talk given a t Atomic Absorption Spectroscopy Conference, Sheffield, England, July, 1969. (115B) Pungor, E., Halls, J. D., Kemiai Kozlenenyek, 31, 49 (1969). (116B) Rann, C. S., Spectrochim. Acta, 23B, 245 (1968). (117B) Zbid., 827 (1968). (118B) Razumov, V. A,, Fishman, I. S., Z h . Prikl. Spektrosk., 10, 710 (1969). (119B) Remy, F., Rev. Chim. Mzneral, 5, 1201 (1968). (120B) Roldan, R., Rev. Sci. Instrum., 40, 1388 (1969). (121B) St. John, P. A., AIcCarthy, W. J., Winefordner, J. D., ANAL. CHEW , 39, 1496 (1967). (122B) Sanematsu. H. S.. Combust. Flame. . 13, i (1969). ’ (123B) Schofield, K., Chem. Rev., 67, 707 (1967). (124B) Schmitz, R. A., Combust. Flame, 11, 49 (1967). (125B) Semenova, 0. P., Gorbunova, T. &I., Bokova, N. A., Sukhanova, G. B., Z h . Prikl. Spektrosk., 10, 937 (1968). (l26B) Shatkay, A., ANAL. CHEM.,40, 2047 (1968). (127B) Silvester, M. D., McCarthy, W. J., Anal. Lett., 2, 305 (1969). (128B) Smith, R., Stafford, C. M., Winefordner, J. D., ANAL.CHEM., . 41,. 946 (1969). (129B) Snelleman, W., Combust. Flame, 11, 453 (1967). (130B) Spitz, J., Uny, G., A p p l . Opt., 7, 1345 (1968). (131B) Stauffer, F. R., Sukai, H., ibid., p 61. (132B) Strojek, R. W., Grover, G. A., Kuwana, T., ANAL. CHEM., 41, 481 (1969). (133B) Stupar, J., Dawson, J. B., A p p l . Opt., 7, 1351 (1968). (134B) Thomas, D. L., Combust. Flame, 12, 541 (1968). (135B) Ibid., p 569. (136B) Tkachenko, V. M., Tyutyunnik, V. B., Opt. Spektrosk., 26, 896 (1969). (13723) Tsukamoto, A., J . Sci. Hiroshima University, Sec. IZA, 32, 15 (1968). (138B) Tull, R. G., A p p l . Opt., 7, 2023 (1968). (139B) Vinckier, J., Van Tiggelen, A., Combust. Flame, 12, 561 (1968). >
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(140B) Williams, D. T., Kolitz, B. L., Appl. Opt., 7, 607 (1968). (141B) Willis, J. B., Fassel, V. A., Fiorino, J., Spectrochim. Acta, 24B, 157 (1969). (142B) Willis, J. B., Rasmuson, J. O., Kniselev. R. N., Fassel. V. A.. ibid., 23B, 72% (1968).’ (143B) Yamada, H. Y., J . Qmnt. Spectros. Radiat. Transfer, 8, 1463 (1968). (144B) Yasuda, K., Bunseki Kagaku, 17, 289 f\ -l R RI8 ) . __
(145B) Zacha, K. E., Bratzel, M. P., Winefordner, J. D., Mansfield, J. M., ANAL.CHEM.,40, 1733 (1968). (146B) Zeegers, P. J.T., Smith, R., Winefordner, J. D., ibid., 40 (13), 26A 11968). \ - - - - I -
(147B) Zeegers, P. J. T., Townsend, W. P., Winefordner, J. D., Spectrochim. Acta, 24B, 243 (1969). Atomic and Molecular Emission Spectrometry
(IC) Aldous, K. M., Dagnall, R. M., Pratt, S.J., West, T. S., ANAL.CHEM., 41, 1851 (1969). (2C) Aldous, K. M., Dagnall, R. M., Thompson, K. C., West, T. S., Anal. Chim. Acta, 41, 378 (1968). (3C) Armstrong, D. R., Ranz, W. E., Ind. Eng. Chem., Process Des. Develop., 7, 31 (1968). (4C) Atwell, M. F., Hebert, J. Y., Appl. Spectrosc., 23, 480 (1969). ($2) Barnett, W. B., Fassel, V. A., Kniseley, R. N., Spectrochim. Acta, 23B, 643 (1968). (6C) Barry, J. E., Donega, H. M., Burgess, T. E., J . Electrochem. SOC., 116, 257 (1969). (7C) Bedrosian, A. J., Lerner, 31. W., ANAL.CHEM.,40, 1104 (1969). (8C) Boettner, E. A., Grunder, F. I., in “Trace Inorganics in Water,” R. A. Baker, Advances in Chemistry Series, No. 73, ACS, Washington, D. C., 1968, p 236. (9C) Borgianni, C., Capitelli, M., Cramarossa, F., Triolo, L., Molinari, E., Combust. Flame, 13, 181 (1969). (lOC) Borovik-Romanova, T., Zh. Anal. Khim.. 24. 974 (1969). (11C) Bueger, P. A., Fink, W., Z . Anal. Chem., 244, 121 (1969). (12C) Ibid., p 314. (13C) Bueger, P., illaierhofer, J., Reis, A., ibid., 234, 176 (1968). (14C) Bueger, P. A., Reis, A., ibid., 235, 181 (1968). (15C) Camubell. 11. H.. ANAL. CHEM.. 40; 6 (1988). ’ (16C) Chapman, J. F., Dale, L. S., Analyst (London), 94, 563 (1969). (17C) Christian, G. D., Anal. Lett., 1, 845 (1968). (1%) Coudert, M., Vergnaud, J. M., C. R. Acad. Sci. Paris, Ser. C, 268, 1225 (1969). (19C) Cowley, T. G., Fassel, V. A., Kniseley, R. N., Spectrochim. Acta, 23B, 771 (1968). (20C) Crider, W., Rev. Sci. Instrum., 39, 212 (1968). (21C) Crider, W. L., ANAL.CHEM.,41, 534 (1969). (22C) Crider, W. L., Strong, A. A., Barkley, N. P., Appl. Spectrosc., 22, 542 (1968). (23C) Czakow, J., Boboli, K., Ney, W., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 709. (24C) Dagnall, R. M., Kirkbright, G. F., West, T. S., Wood, R., Anal. Chim. Acta, 47, 407 (1969). (25C) Dagnall, R. M., Smith, D. J., Thompson, K . C., West, T. S.,Analyst (London), 94,871 (1969). ~
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(26C) Dagnall, R. M., Thompson, K . C., West, T. S., Analyst (London), 93, 72 (1968). (27C) Ibid., p 153. (28C) Ibid., p 518. (29C) Ibid.; 94, 643 (1969). (30C) Dean, J. A., Fues., R. E., Anal. . L e i 2, lob (1969). (31C) Dean, J. A., Morrow, R. W., Anal. Lett.. 1. 619 - ~ (1968). (3%).Dickinson, G. W., Fassel, V. A., ANAL.CHEM.,41, 1021 (1969). (33C) Eckert, H. U., Kelly, F. L., Olsen, H. N., J. Appl. Pkys., 39, 1846 (1968). (34C) Evans. C. C.. Grimshaw. H. M., Tuhnta, 15,413 (1968): (35C) Fagan, A. W., Klein, H. M., ANAL. CHEM.,40, 2041 (1968). (36C) Fassel, V. A., Becker, D. A., ibid., 41, 1522 (1969). (37C) Fiorino, J. A., Kniseley, R. N., Fassel. V. A.., Svectrochim. Acta. 23B. . 413 (1968). (38’2) Folsom, T. R., Sreekumaran, C., Weitz, W. E., Tennant, D. A., Appl. Spectrosc. 22, 109 (1968). (39C) Gol’dfarb, V. RL, Goikhman, V. Kh., Zh. Prikl. Spektrosk., 8, 193 (1968). (40C) Gol’dfaFb, V. M.,. Goikhman,. V. Kh., Dresvin, S. V., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967 p 751. (41C) Goleb, J. A., Middelboe, V., Anal. Chim. Acta, 43, 229 (1968). (42C) Grimm, W., Spectrochim. Acta, 23B, 443 (1968). (43C) Gutsche, B., Herrmann, R., Z. Anal. Chem., 242, 13 (1968). (44C) Gutsche, B Herrmann, R., Rudiger, K., ibid., ~ ’ 5 4 . (45C) Haljamae, H., Larsson, S., Chem. Instrum., 1,131 (1968). (46C) Harrison, W. W., Wadlin, W. H., ANAL.CHEM.,41, 374 (1969). (47C) Hell, A., Ulrich, W. F., Shifrin, N., Ramirez-Munoz, J., Appl. Opt., 7, 1317 (1968). (48C) Herrmann, R., Gutsche, B., Analyst (London) 94, 1033 (1969). (49C) Hieflje, G. M., Malmstadt, H. V., ANAL.CHEM.,41, 1735 (1969). (50C) Hingle, D. N., Kirkbright, G. F., Bailey, R. M., Talunta, 16, 1223 (1969). (51C) Hingle, D. N., Kirkbright, G. F., West, T. S.,Analyst (London), 93, 522 (1968). (52C) Ibid., 94, 864 (1969). (53C) Hirokawa, K., Goto, H., Bull. Chem. SOC.Jap., 42, 693 (1969). (54C) Hobbs, R. S., Kirkbright, G. F., Sargent, RI., West, T. S., Talunta, 15, 997 (1968). (55C) Hobbs, R. S.,Kirkbright, G. F., West. T. S., Analyst (London), 94, 554 (1969). ’ (56C) Hoffman, E., Holdt, G.,, in “Proceedings of the XIV Cclloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 733. (57C) Hwang, J. Y., Sandonato, L. M., Anal. Chim. Acta, 48, 188 (1969). (5$C) Kalvina, I. N., Opt. Spektrosk., 25. 173 (1968). (59C’) Kamada, H., Oda, S., Hori, T., Bunseki Kagaku, 17, 469 (1968). (60C) Katz, G. M., Anal. Biochem., 26, 381 (1968). (6lC) Kirkbright, G. F., Sargent, M., Analust (London). 93, 552 (1968). (62C) Kirkbright, ’G. F., Sargent; M., West, T. S.,At. Absorption Newsl$tt., 8, 34 (1969). (63C) Kirkbright, G. F., Sargent,, M., West, T. S.,Talunta, 16, 245 (1969). (64C) Kirkbright, G. F., Semb, A., West, T. S., Spectrosc. Lett., 1, 7 (1968). I
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ANALYTICAL CHEMISTRY, VOL. 42, NO. 5, APRIL 1970
(65C) Kirkbright, G. F., Semb, A., West, T. S.. Talunta. 15.441 (1968). (66C) Kirkbright, ‘G. F~.,West, T. S., Appl. Opt., 7, 1305 (1968). (67C) Kirkbright, G. F., Wilson, S. J., Spectrosc. Lett., 2, 225 (1969). (68C) Kleinmann, I., Svoboda, V., ANAL. CHEM.,41, io29 (i969). ’ (69C) Kniselev. R. N.. Butler.’ C. C.. ’ Faksel, V. A:,’ibid., p 1494. (70C) Koirtyohann, S.R., Pickett, E. E., ANAL.CHEM.,40, 2068 (1968). (71C) Koirtyohann, S.R., Pickett, E. E., in “Proceedings of the XI11 Colloquium Spectroscopicurn Internationale,” Hilger, London, 1967, p 270. (72C) Koirtyohann, S.R., Pickett, E. E., Spectrochim. Acta, 23B, 673 (1968). (73C) Kranz, E., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 697. (74C) Laqua, K., Massmann, H., Schirrmeister, H., ibid., p 725. (732) Larkins. P. L.. Lowe. R. M.. ‘ Suilivan, J. Walsh, A., Spectrochim: Acta, 24B, 187 (1969). (76C) Lassale, J., Roig, J., C. R. Acud. Sci., Paris, Ser. A B , 268B, 27 (1969); (77C) Lebedev, V. I., Zh. Anal. Khzm., 24, 337 (1969). ‘ (78C) Maksimov. D. E.. Ridnevskii. N. K.; Tr. Khim. Tekhnol:, 1968, (2) 56. (79C) Malakoff, J. L., Ramirez-Munoz, J., Aime, C. P., Anal. Cham. Acta, 43, 37 (1968). (80C) Mansell, R. E., Appl. Spectrosc., 22, 790 (1968). (81C) Mansfield, J. M., Winefordner, J. D., -4nal. Chim. Acta, 40, 357 (1968). (82C) Margoshes, RI., Rasberry, S. D., ANAL.CHEM.,41, 1163 (1969):. (83C) Marinkovic, V.,Dimitrijevic, B., Spectrochim. Acta, 23B, 257 (1968). (84C) Matic, J. S., Pesic, D . S., Appl. Spectrosc., 22, 63 (1968). (85C) Mermet, J. hl., Robin, J. P., ANAL. CHEM.,40, 1918 (1968). (86C) Mermet, J. M., Robin, J., in ‘‘Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 715. (87C) Milazzo, G., ibid., p 667. (88C) Pvlilazzo, G., Cecchelli, G., Appl. Spectrosc., 23, 197 (1969). (89C) RIitteldorf, J. J., Landon, D. O., Appl. Opt., 7, 1431 (1968). (9OC) Mossotti, V. G., Duggan, M., ibid., D 132.5. ( S i c ) Murayama, S., Matsuno, H., Yamamoto, hl., Spectrochim. Acta, 23B, 513 (1968). (92C) Parsons, hl. L., Anal. Lett., 2, 229 (1969). (93C) Pevtsov, G. A., Krasilshchik, V. Z., Yakoleva, A. F., Zh. Anal. Khzm., 23, 1785 (1968). (94C) Ibid., 24, 234 (1969). (9RC) Pforr, G., in “Proceedings of the XIV Colloquium Spectroscopicurn InternationaleJJJ Hilger, London, 1967, p 687. (96C) Pickett, E. E., Koirtyohann, S. R.‘ ANAL.CHEM.,41, (14) 28A (1969). (97C) Pickett, E. E., Koirtyohann, S. R., Spectrochim. Acta, 23B, 235 (1968). (98C) Ibid., 24B, 325 (1969). (99C) Pleskach, L. I., Zh. Anal. Khim., 24, 1468 (1969). (1OOC) Pleskach, L. I., Beremzhanov, B. A,, Izv. Akad. Nauk. Kaz. SSR, Ser. Khim.. 19. (2) 5 (1969). (101C) Pleskach, L. I.,’Rykov, N. A., Zh. Anal. Khim., 24,250 (1969). 1102C) Pribram. J. K.. Pevchina. C. hI.. ‘ A i i l . Opt., 7,’2005 (1968). (103C) Pueschel, R. F., J . Colloid Interjac. Sci., 30, 120 (1969). ’
v.,
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(104C) Pungor, E., Szasz, A., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 1125. (105C) Pungor, E., Szasz, A., Talanta, 16. 269 11969’1. (106C) Rains, T . C., Menis, O., Spectrosc. Lett., 2, 1 (1969). (107C) Riley, J. P., Taylor, D., Anal. Chim. Acta, 42, 548 (1968). (108Ci Robertson. D. E., ANAL.CHEM., ’ 40, 1067 (1968).‘ (lO9C) Rocchiccioli, C., Townshend, A., Anal. Chim. Acta, 41, 93 (1968). (llOC) Rossi, G., Hainski, Z., Omenetto, N., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 675. (111C) Rossi, G., Mol, M., Spectrochim. Acta, 24B, 389 (1969). (1lZC) Ruediger, K., Gutsche, B., Kirchhof, H., Herrmann, R., Analyst (London), 94, 204 (1969). (113C) Sastri, V. S., Chakrabarti, C. L., Willis, D. E., Can. J . Chem. 47, 587 (1969). (114C) Sastri, V. S., Chakrabarti, C. L., Willis, D. E., Talanta, 16, 1093 (1969). (1132) Scaringelli, F. P., Rehme, K . A., ANAL.CHEM.,41, 707 (1969). (116C) Schirrmeister, H., in “Proceedings of the XIV Colloquium Spectroscopicum Internationale,” Hilger, London, 1967, p 729. (117C) Schirrmeister, H., Spectrochim. Acta, 23B, 709 (1968). (118C) Semenova, 0. P., Gorbunova, T. hl., Bokova, N. A., Sukhanova, G. B., Zh. Prikl. Spektrosk., 9, 937 (1968). (119C) Shatkay, A., ANAL.CHEM.,40, 2097 (1968). (120C) Skogerboe, R . K., Todd, R., hlorrison, G. H., ibid., p 2. (121) Smith, R., Winefordner, J. D., Spectrosc. Lett., 1, 157 (1968). (122) Smith, R., Stafford, C. Rl., Winefordner, J. D., Anal. Chim. Acta, 42 523 (1968). (123C) Spitz, J., ‘Ciny, G., Appl. Opt., 7, 1345 (1968). (124C) Spitz, J., Uny, G., ROUX,M., Besson, J., Spectrochim. Acta, 24B 399 (1969). (1292) Stupar, J., Dawson, J. B., Appl. Opt., 7, 1351 (1968). 1126Cl Stmar. J.. Daivson. J. B.. At. Abs&pti/n ;?ewslett., 8 , 38 (1969): (127C) Suzuki, M., Bunseki Kagaku, 17, 1529 (1968). (128C) Ibid., 18, 176 (1969). (129C) Syty, A , , Ph.D. Thesis, University of Tennessee. 1968: Dissertation Abstr., 29. 1583B 11968). ’ (130C) Syty,‘A., Dean, J. A., Anal. Lett., 1. 241 (1968’1. (131C) Syty, A., Dean, J. A., Appl. Opt., 7, 1331 (1968). (132C) Szivek, J., Jones, C., Paulson, E. J., Appl. Spectrosc., 22, 195 (1968). (133Ci TODD. J. A.. Schroetter. H. W.. Hacker,*H., Rev: Sci. Instrum., 40; 1164 (1969). (134C) Trampisch, W., Herrmann, R., Spectrochim. Acta, 24B, 215 (1969). (135C) Veillon, C., Margoshes, M., ibid., 23B, 503 (1968). (136C) Ibid., p 553. (137C) Venghiattis, A. A., Appl. Opt., 7. 1313 11968). (13dC) West, C. D., ANAL.CHEM.,40, 253 (1968). (139C) Wildy, P. C., in “Proceedings of the XI11 Colloquium Spectroscopicum Internationale,” Hilger, - . London, 1967, p 295. (140C) Willis, J. B., Fassel, V. A., Fiorino, J. A., Spectrochim. Acta, 24B, 157 (1969). (141C) Woodriff, R., Appl. Spectrosc., 22, 207 (1968). ~
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(142C) Woodriff, R., Siemer, D., ibid., 23, 38 (1969). (143C) Woods, J . S., ibid., 22, 799 (1968). (144C) Zeegers, P. J. T., Townsend, W. P.. Winefordner. J. D., Smctrochim. Acta, 24B, 243 (1969). I
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Atomic Absorption Spectrometry
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(3D) Bache, C. A., Lisk, D. J., ibid., p 2224. (4D) Backer, E. T., Clin. Chim. Acta, 24, 233 (1969). (5D) Bailey, B. W., Rankin, J. ?*I., Spectros. Lett., 2, 159 (1969). (6D) Ibid., p 233. (7D) Belyaev, U. I., Ivantsov, L. RI., Karyakin, A. V., Phi, P. H., Shemet, V. V., Zh. Anal. Khim., 23, 508 (1968). (8D) Berge, D. G., Pflaum, R . T., Lehman, D. A., Frank, C. W., Anal. Lett., 1. 613 11968). (YD’) Bernas, B., AXAL.CHEY.,40, 1682 (1968). ~-”-~,-
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(35D) Donaldson, E. hI., Charette, D. J., Rolko, V. H. E., Talanta, 16, 1305 (1R6R\. \ - - - - /
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(74D) Kumamaru, T., Anal. Chim. Acta, 43, 19 (1968). (75D) Langmyhr, F. J., Paus, P. E., ibid., D 397. (76D) Law, S. L., Green, T. E., ANAL. CHEM.,41, 1008 (1969). (77D) Ling, C., ibid., 40, 1876 (1968). (78D) Lowe, R. M., Spectrochim. Acta, 24B, 191 (1969). (79D) L’vov, B. V., ibid., p 53. (80D) L’vov, B. V., Zh. Prikl. Spektrosk., 8, 517 (1968). (81D) L’vov, B. V., Kabanova, hl. A., Katskov, D. A., Lebedev, G. G., Sokolov, hl. A., Zh. Prikl. Spektrosk., 8, 200 (1968). (82D) L’vov, B. V., Katskov, D. A,, Lebedev, -~ G.-G.L ibid., 9, 558 (1968).
B. V., Plyuschch, I
,I., Winefordner, J. D., ANAL.CHEM.,41, 946 (1969). (44E) Smith, R., Stafford, C. hl., Winefordner, J. D., Can. Spectrosc., 14, 2 (1969).
(45E) Sychra, V., Matousek, J., hls S., Chem. Listy, 63,177 (1969). (46E) Vickers, T. J., Merrick, 8. Tahnta, 15, 873 (1968). (47E) Vickers, T. J., Vaught, R. ANAL.CHEM.,41,1477 (1969). (48E) West, T. S., Williams, X . ibid., 40, 335 (1968). (49E) West, T. S., Williams, X. K., A Chim. Acta, 42, 29 (1968). (50E) Ibid., 45, 27 (1969). (51E) Zacha, K . E., Bratzel, 31. Winefordner, J. D., Mansfield, J. ANAL.CHEM.,40,1733 (1968).
Raman Spectrometry Ronald E. Hester, Chemistry Department, University of York, England
T
HI^ REVIEW covers the literature which appeared between late 1967 and late 1969, but in a highly personal, non-comprehensive manner. The growth of activity in this area, primarily due to the widespread application of lasers as Ranian light sources, has resulted in a volume of literature which it is not possible to deal with comprehensively in a short article. Since the preparation of the previous review in this series ( I ) , the first two volumes of that excellent Specialist Report series of The Chemical Society dealing with “Spectroscopic Properties of Inorganic and Organometallic Chemistry” have been published ( 2 ) . These works do attempt to cover the “vast majority” of papers concerned with application of the Raman technique (and others) in inorganic and organometallic chemistry, and this reviewer warmly commends them to the reader. Several other books and reviews which cover various aspects of the field of Raman spectrometry have been produced, and a personal selection of these appears in the bibliography appended to this article. I n order to avoid cluttering this narrative unnecessarily with numbers, only a limited selection of the references quoted are designated by numbers in the text, those which are so designated being selected so as t o aid the reader in finding his way through the bibliography. Further simplification is achieved by dividing the references into subject categories, and presenting them in the order of their discussion in the text, rather than as an alphabetical listing based on first-named authors. It is hoped that the reader will find these changes from the usual form of review presentation helpful to his rapid comprehension of the material discussed, and that those whose valuable contributions have been neglected or inadequately surveyed will be generous in their forgiveness and understanding.
EXPERIMENTAL TECHNIQUE
This has been a period of steady progress in the development of Raman instrumentation and technique. The excellent Jarrell-Ash (U.S.A.) spectrometer has come into full production, as have new instruments from Spectra Physics (U.S.A.), Huet (France), and Japan Electron Optics Laboratory Co. (Japan), joining the upgraded instruments from Perkin-Elmer (U.S.A.), Coderg (France), Cary and Spex (G.S.A.). A11 these spectrometers employ cw laser light sources. He-Xe lasers still are most commonly used, but the predicted reduction in price of ion lasers ( 1 ) has enabled many uSers to employ krypton and argon gas lasers during the period reviewed, the argon laser being particularly advantageous for gas-phase studies, due to its high power (6 watts available commercially) in the blue and green regions of the spectrum. A number of other Raman spectrometer systems have been described, one of them using the doublebeam principle (26) to help discriminate against stray light and grating ghosts which tend to interfere at very low frequencies (23). Other solutions to this problem have been proposed, most of them employing narrow band interference filters, sometimes combined u i t h chopper systems (24). I n addition to the rapid development of relatively inexpensive (say $5000) and reliable ionized gas lasers, interesting source developments have been in the application of solid state pulsed lasers. Quasi-continuous operation of a ruby laser a t 50 Hz, with a pulse amplifier and a linear gate which is opened only during the (1 msec) laser emission, and suppresses the photomultiplier detector noise in the remaining time (19 msec), has been shown to produce very good signal/noise performance. Further progress has been made in the development of tuneable lasers (27-
Attention has been paid to the problems of efficiently eliminating plasma lines from gas laser discharges, of beam focussing into the sample area, and coupling the Raman scattered light to a monochromator, and generally to optimising the sample illumination geometry, using lasers as light sources (31-34). At the other end of the monochromator, photon counting systems using photomultipliers have become the most popular general purpose Raman detectors, though other detection systems are better for certain applications. For example, work with very hot samples calls for ac phase-sensitive detection, and image intensifier phototubes coupled with storage video equipment have been put to good use for very fast (-20 nsec) recording of spectra. Help in eliminating recording errors has been provided by papers dealing with continuously scanning spectrometers, routine frequency calibration, and the calculation of the Raman shift in vacuum (41-43). A report a t the recent Ottawa Raman Conference (44) M arned against the convergence errors commonly made when measuring depolarization ratios by simple rotation of a half-wave plate in the laser beam before the sample. Polarization measurements using 180’ laser illumination have been reported. A major advantage of using laser illumination is the smallness of the sample size required. Improvements in the techniques for dealing with very small samples have been made, and excellent spectra from a few nanolitres of liquid (46) and gas (33) have been published. The versatility of the laser source has eased the design problems for sample cells required to operate a t temperatures both higher and lower than ambient, and has made it possible to obtain Raman spectra from solids, liquids and gases at very high pressures
SO).
(54-58).
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