Reniew of
APPLIED ANA LYSIS
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AUTOMATIC OPERATIONS IN ANALYTICAL CHEMISTRY G. D. Patterson, Jr. E. I . du Pont de Nemours 8 Co., Inc., Wilmington, Del.
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major advances in the application of new principles to automatic analysis have not been very evident in the past two years, a large number of very striking modifications leading to improved reliability and versatility have appeared. This paper follows the same approach as past reviews (204). An impressive array of papers have been concerned with economic and social effects of automation, as exemplified (66) by H. B. du Pont a t the Convention of the Instrument Society of America, September 1958. His point was that modern instrumentation must be considered as a main source of the extra hands needed to keep our standard of living a t its continuing rate of increase-which in 20 years mill require twice the output our economy provides today. Instruments are essentially devices for measuring physical phenomena in terms of a quantitative record which is the essence of science itself: “Measurement is a universal language, one through which men of many tongues find a common method of communication.” Bright (25) listed eight “myths of automation” and tabulated the motives and benefits of automation in 13 firms. Cunningham (47) discussed the fundamentals of automation with emphasis on “hunting,” feedback, and computation, while Kaye (134) reviewed ways in which automation “serves the research worker.” Astin (10, 11, 122) has examined the general situation in instrumentation and measurement. His statement that no area of science is more critically affected by instrumentation, or its lack, than materials development and evaluation, will be strongly seconded by many analytical chemists. HILE
GENERAL TRENDS
A number of authors have discussed trends in laboratory instrumentation. Lewin (152) presented characteristics of modern instrumentation and principles of instrument construction, as well as typical instruments and an outlook on the future. The approach in categorizing the principles of instrument design, based on the n a y in which the basic elemcnts of an instrument can be put together, should prove useful t o both experienced analytical chemists and students. His closing thoughts are: “It is not enough that the modern analyst merely be capable of recognizing 646
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malfunctioning of an instrument. It is essential that the instrumental analyst understand basic electronics and optics and that he have a t least a rough picture of what is inside the “black box” and that he be capable of performing periodic checking tests to confirm the proper operation of components and circuits.” Muller’s Beckman an-ard address (192). “Adventures in Instrumentation,” emphatically confirms the belief of many people that instrumentation is a vast subject which can hardly be comprehended by a single person. There is n pronounced need for a unified and general approach to the instrumentation field, including detection, measurement, recording, control, and data assimilation. In commenting that instrumentation is largely responsible for our technological advance, he also stressed the need for basic research in rare and obscure phenomena which today appear insignificant, but which could become the industrial practice of tomorrow. I n m m (160) discussed in general terms the value of automatic laboratory instruments. Borries (19) discussed the use of instruments in measuring and investigational techniques in various natura1 sciences. while Walter (27.2) described briefly the steps in building a laboratory device for automatic analysis. He emphasized that in some cases automatic laboratory analyses can be justified because of the advantages of uniform procedure, even when the economics of automaticity offer little attraction. Programmed control of complex chemical analyses may present special advantages for both routine and occasional operations. Walter (271) has reviewed analytical chemistry in conjunction nith satellite research, including a panorama of the analytical possibilities of the satellite program. Automatic measurement is an essential part of man’s study of space. He predicts that the work of the analytical chemist will be vital in the development of the space age, just as it was the nucleating center around which the atomic age crystallized. Thomson (268) divided the probIems of instrumentation into two categories: determination of what is to be measured, followed by investigation of hov to make the measurement. His attention n-as centered on recent developments in transducers which provide an electrical signal. Kidwell (137) is concerned with
instruments and their components. He listed equipment for a standards laboratory and discussed the philosophy of tests and calibration schedules. Combs and coworkers (41) and Mahood (163) have been concerned with maintenance aspects and reduction of down time of electronic instruments and process stream analyzers. The specifications established by the American Standards Association for the automatic null-balancing of electrical measuring instruments (123) should prove useful. Several papers presented a t the Instrument Society of America conference (September 1958) dealt with electronic instruments used in various industries and with the requirements and desired improvements for applications in various industries (180, ,202, 211,252). The proceedings of the 1957 National Conference on Instrumental Methods of Analysis (111) contains a number of general papers. Crawford (45) has described computer simulation of process control system performance before the plant is built to verify the need for features not available in existing instrumentation. Papers such as those by Thomas (156) and Byran and Romanovsky (50) dealt 1%-ithair pollution measurement. The latter paper is a thorough review of the air-monitoring program of the Los Angeles air pollution control district, including monitoring and recording instruments for sulfur dioxide, oxidants, carbon monoxide, nitric oxide, nitrogen dioxide, particulate sampling, and ozone. The basic instrument types were revierred in some detail, and one main conclusion was that much room exists for further development to provide instruments which are both more sensitive and have greater specificity a t reduced costs and size. TWOgeneral papers dealt with the problem of measuring sulfur dioxide in the atmosphere (46, 95). Cummings and Redfearn (46) encountered the old difficulty of calibration a t extremely low concentrations, R hich was overcome by using a method in which the sulfur dioxide and air were flowing continuously to eliminate varying adsorption and desorption of sulfur dioxide on the Fvalls of vessels. Littman et al. (156) described the use of a continuous oxidant recorder for measuring ozone in the atmosphere. Holmes and Johnson (113) reviewed briefly the special
problems of probing the upper atmosphere. The high toxicity of many organophosphorus compounds has created special problems in the detection of small amounts of toxic phosphorus compounds, and Kramer and Gamson (141) reviewed analytical methods developed by the Army Chemical Corps to meet this challenge. Moore and Ettinger (185) maintain that efficient control of waste discharge in water must be based on analytical methodology, although the latter does not appear to be keeping pace with the problems. BOOKS
A number of books on analytical instruments have been published (49,1.29, 280). The “Guide to Instrumentation Literature” by Brombacher et aZ. (27) should be useful in specifying or designing instruments. Banner (12) discusses generally electronic measuring instruments. Instrumentation or automation books published for use in other fields are also helpful. They include “Electronic Instrumentation for the Behavioral Sciences” by Brown and Saucer (.28), “Encyclopedia of Instrumentation for Industrial Hygiene” by Yaffe et al. (286), and “Automation in Business and Industry” by Grabbe (94). Kumerous books or new editions deal with automatic process control, such as those by Considine (424, Echman (GO), Holzbock ( 1 1 4 , Laning and Battin (Ids),and Young (287). The increasing importance of physical optics in analytical instrumentation calls for knowledge of books such as the one by Houstoun (116) “Physical Optics.” PROCESS ANALYSIS
Information useful t o analytical chemists can occasionally be found among the multitude of papers published on process control, although much unnecessary duplication appears in the current literature in this field. The columns by Kall on instrumentation in Industrial and Engineering Chemistry and by Muller in ASALPTICALCHEMISTRY are must reading-e.g. (191, 267, 269). Kall has cited numerous instances where a team approach has proved most productive; instrumentation, production, and analytical personnel, all contributing to a process or to a process development, in order to obtain optimum results. Abroad, interest on the automatic measurement of quality in process plants has been indicated (26, 191). Papers presented a t the Instrument Society of Bmerica conference (September 1958) dealt with problems in the proper selection of process instruments. Kebber ( n 4 ) concerned himself 11itli the economic evaluation of a process instrument. This must usually be made in terms of factors external t o the instrument itself, mhich
reveals that instruments per se have no value. Savitzky (226) compares continuous composition analyzers, using as an example infrared analyzers versus the new process gas chromatographs. Albright ( 7 ) described a ‘hew” approach to the selection of process stream analyzers based on fundamental matter-energy relationships that can be established and observed quantitatively as instrumental techniques. He divides the variables which may be measured into four basic groups: electronmagnetic radiation, chemical affinity or reactivity, electrical or magnetic fields, and thermal or mechanical energy. Aikman in reviews (4, 6) of process control by analytical instrumentation, divided all methods into nonspectroscopic and spectroscopic! I n a review of the measurement aspects of process control, he later (6) emphasized that the control of a process cannot be better than the quality of the measurements made on the process. These measurements are limited in quality both in a static sensee.g., by accuracy-and in a dynamic sense (by time lag). The problems and advantages of continuous chemical analyzers have been discussed (35,269). A large number of papers and general reviews concerning process automation deserve mention. Noebels (201) considered continuous stream analyzers to be in effect small, highly specific, automatic laboratories designed to provide primary analytical information of the required degree of accuracy and reliability for optimum process operation. Other general revieits have included one (125) on continuous chemical analysis by optical methods, another (64) on the advantages of electronic controls in process instrumentation, and a discussion (207) of the different instruments used in automatic analysis in process control. Kallis and Tonmend (270)have considered the effects of the four basic functions (information, communication, evaluation, action) in the operation of any organization or system and on trends and developments in instrumentation. Fraade (71)has published a review covering seven major types of “true” continuous process stream instruments, including mass spectrometry, infrared, refractometry, viscosity, gas chromatography, flow colorimetry. and moisture. Karp (133) sketched briefly the fundamental methods of analytical measurement, including the types of output obtainable with analysis instrumentation. He discussed the problems of sample handling, correlation of the desired product to specification n-ith the analysis technique, and the role of computers in interpreting analytical data. il series of papers (119) comprising a progress review of process instrumentation includes information on infrared analysis, instrumentation in the nuclear energy field,
refractometers, oxygen analyzers, mobile data loggers, and a critical survey of chemical developments abroad. THE SAMPLE
The problems of obtaining a representative sample for any analysis, automatic or othern-ise, are always present. Although few papers have appeared dealing specifically with sampling problems, papers describing an automatic analysis should include some mention of how sampling may reliably be accomplished. Aikman ( 6 ) has discussed the long transport lag encountered by sampling systems when analysis instruments are placed inside a process control loop. He presented methods for estimating the effect of these lags on control work and how lag difficulties can be partially remedied. Problems associated with data sampled from refractometers, mass spectrometers, and nuclear magnetic resonance analyzers were discussed. Often, the separation operation will be accomplished a t the same time that the sample is taken. Several authors have looked into techniques of obtaining gas samples. Sturgis (246) described new techniques for sampling and analyzing exhaust gases to provide reliable information on the contribution of automobile exhaust to air pollution. Jacobs and Hochheiser (126)and Thomas et al. (257) described means for automatic sampling of atmospheric gases for the purpose of determining nitrogen oxides. RIaley (168) discussed sampling problems for measurement of trace contaminants in process streams. He pointed out that the continuous measurement of trace contaminants often presents more severe sample handling difficulties, as well as analysis problems, than those encountered n hen measuring major constituents. Special care in preventing loss of the contaminants by sorption, and special tricks to obtain desired sensitivity and sclectivity may be involved. Examples included continuous sampling of a liquid oxygen stream for acetylene contamination, catalytic oxidation of hydrocarbon contaminants in air or oxygen with resultant carbon dioxide measurements, and mater contamination in hydrocarbon streams. Hc also described special sampling techniques t o obtain maximum sensitivity for infrared determination of acetylene in ethylene and for measuring dew points Kith a nondispersive infrared analyzer t o - 100” F. du Ruisseau (67) has described sample depositors for paper chromatography based on forcedflow applicators TI here the rate of flow can be controlled. THE DESIRED CONSTITUENT
Separation and Treatment.
Pre-
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vious predictions concerning the everpresent problem of separation of either desired or undesired constituents in many quantitative analyses are borne out by the large number of papers on this subject. As n-ith sampling, the solution t o separation problems may have been considered a secondary aspect of the over-all analytical problem and hence buried in articles primarily concerned n-ith other problemsfor example, measurement techniques. Both column and paper chromatography have seen much activity during the past two years. Svensson (248) has described an apparatus for continuous chromatographic separation. Main and coworkers (164) developed a constantrate flow device for electrolytic eluents in column chromatography which delivers 3 to 5 ml. per hour a t a constant rate for periods of unattended operation up to 2 weeks. Martin (176) described a useful automatic starter for chromatograms. Levenbook (151) described a quantitative method for the automatic application of milliliter quantities onto paper chromatograms. Johansson et al. (127) found continuous separation of bile acids by chromatographic means t o be very efficient. The use of automatic ion exchange columns, primarily for the separation of amino acids, has been the subject of several studies (172, 230, 237). Gas chromatography has also seen accelerating development. Martin (175) has reviewed the past, present, and future of gas chromatography, concluding with the prediction that a tie-in of the gas chromatograph with other laboratory equipment provides the answer to the automatic chemist. Spracklen (239) reviewed the development of gas chromatographs and stated that in the past, plant stream analyzers have followed similar laboratory instruments by a t least 5 years or more. He points to the gas chromatograph as an important exception to this time lag. Savitzky (226) commented also on the marked upsurge in the design of chromatographic analyzers for plant use, giving a review of the problems involved and types of instrumentation being developed to meet the challenge. hfcGovern and Carlisle (161) have described the application of a gas chromatograph to petroleum refining, where the instrument was used to improve performance in an alkylation unit. Heilbronner et al. (107) described a fully automatic gas chromatographic column for preparative purposes which can be programmed to feed a sample of preselected size from a batch of mixture into the column, separate the sample into its components, and feed the components into their respective cooling traps according to the program. This sequence of operations can be repeated automatically a chosen number of times.
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Desty (52) has reviewed papers concerned with column packings, including effects on peak sharpness, the parameters determining column efficiency, and the use of metal salts as column liquids. Golay (91) has made a theoretical study of chromatographic columns, proposing a performance index which is claimed to be reasonably invariant under a large range of conditions. Kovats and coworkers (140) have also investigated automatic gas chromatography for preparative purposes and described the characteristics important in obtaining efficient and complete separation of ho-component mixtures. Fuller (76) has reviewed the place of gas chromatography in plant stream analyses. Continuing activity in devising unique new types of fraction collectors and droplet counters, etc., is evident. Riggle and Crisp (215) have described a versatile droplet counter, while Baumstark (15) has devised an improved splash tube for drop-counting fraction collectors. This eliminated difficulties in alignment of the open splash tube in the phototube unit used to count drops and in the re-evaluation of drop size when it fluctuated because of temperature or a change in the type of column used. Childs and Picchioni (39) have devised an economical, highly efficient drop counter through the use of an inexpensive miniature transistor photodiode and a new principle for activating this photocell. This counter accurately records drops of liquids a t rates varying from 1 to 700 per minute. Several types of fixed volume fraction collectors involving timing devices, photoelectric operation, etc., have been described (20, 62, 261, 282). Continued utility of extraction methods in automatic separation is evident in Kienberger's (138) paper on an automatic solvent extraction apparatus for determining uranium and in a paper by Raymond (209) describing the construction and operation of a compact and flexible countercurrent distribution apparatus involving automatic drives, electric switches, and specially designed tubes to reduce cocurrent flow. Morrison (188) has described a dustograph, a portable instrument for the rapid collection of dust from the atmosphere by impingement on a moving ribbon of acetate film. Separations involving volatilization and/or combustion have been the subject of a number of papers. Four papers described the automatic combustion of organic compounds for determining carbon, hydrogen, sulfur, the halogens, nitrogen, and oxygen (3, 17, 139, 378). Humphiett (117) discussed an automatic receiver for continuous vacuum distillation, while Hensel and Jones (109) devised an automatic mechanical lowering device
for use in the ASTM determination of volatile matter in coal, coke, and char. MEASUREMENT
Gravimetry. Recognition of the utility of recording thermobalances is evident from the number of papers published on this subject describing both new instruments and their applications. Campbell and Gordon (51) described a simple conversion for making an analytical balance record automatically weight changes, by using the hydrostatic principle and measuring beam deflection by a linear variable differential transformer whose output signal was indicated on a potentiometric recorder. Another inexpensive, automatic, recording thermobalance has been described by Wendlandt (275). It was built from a torsion balance having a 120-mg. capacity. The null position of the balance was maintained by use of a beam of light falling between two photocells. Hooley (115) described a recording quaytz-spring balance with which weight changes up to 1000 mg. can be followed on samples weighing up to 10 grams. This balance permits the sample to be under vacuum or pressure during the operation. Katers (273) described two types of thermobalances which automatically record both the differential and cumulative weight losses during pyrolysis of samples. Displacement of the balance beam due to changes in weight is converted into an electrical signal I-,hich operates a servomechanism to restore the counterbalancing force a t the necessary rate. Groot and Troutner (9'7)gave construction and operation details of an automatic, recording thermobalance made from standard laboratory equipment. Unbalance was detected by a photoelectric null point detector n-hich then operated a servomechanism. Garn (78) described an electronically controlled null point, automatic, recording balance, utilizing a linear variable differential transformer as the sensing element Modifications and accessories to the Chevenard thermobalance have been described by Newkirk (199) and Powell (206). The latter's modification enables this balance to record simultaneously, on separate charts, both thermogravimetric and differential thermal curves of a single sample undergoing thermal decomposition. Bartlett and Williams (IS) devised a balance based on strain gage wires, for the specific evaluation of the relative oxidation resistance of a series of molybdenum alloys. Weight-change rates from 3 to 70 mg. per minute were achieved as well as the detection of lower rates of 0.1 mg. per hour. Stephenson et al. (241) described the automatic
recording of weight and temperature in vacuum sublimation studies. I n their apparatus the sample was suspended a t the end of a copper wire attached to a spring. Optical recording was used. A number of papers have reported applications of thermobalances to sulfates (50, 51), chemical analytical standards (58), complex mixtures of hydrates (96), organometallic precipitates (276, 277), and military pyrotechnic materials (111). Volumetry and Manometry. Young (289) has described an automatic (constant-volume) manometer of simple construction and vride range of sensitivity and response. Gordon and Campbell (93) have constructed an automatic recording buret which provides for continuous recording of changes in volume. The apparatus includes interchangeable metal bellows a t the bottom of the buret which measure the pressure a t the height of the liquid. Deflections of the bellows are measured by a linear, variable, differential transformer, rendering it useful as a titrating or as a gas buret. Mitoff and Pask (183) have reported a recording, differential, thermal expansion apparatus (intended for ceramic testing) which measures and reports the difference in thermal expansion and shrinkage between tivo samples by providing an automatic tracing of expansion versus temperature. Schwab and Neuwirth (228) have described a new method of continuous gas analysis based on manometric measurement of the quantity of flowing gases. Hack (100) has given a brief account of a recording manometer based on a simple method of maintaining the position of the mercury meniscus within less than 1 mm. when pressure changes up to 1 c m . of mercury per minute occur. Farquharson and Kermicle (65) have dcveloped along similar lines, an instrument to find the level of mercury in a glass tube automatically and indicate the value. Densimetry and Viscometry. Hargens (102) has described a liquid density instrument employing transistors for detecting the position of hydrometer floats. I t derives its sensitirity from a miniature differential transformer and associated transistor electronics. Fisher (69) has described a falling-drop timing circuit, with automatic reset, for use with a falling-drop densimeter. It is based on Stoke's law of determining density by noting the time of fall of a droplet, which takes 1 lace between two light beams. Minard (182) has reviewed the problem of viscosity measurement and its utility as a process variable. Samyn and Mattocks (224) devised an automatic viscometer for rheological measurements of pharmaceutical suspensions, both Newtonian and non-
Kewtonian fluids. McKennell (160) devised a cone-plate viscometer involving a flow-curve recorder capable of plotting a curve in 15 seconds with uniform shear acceleration. This device provides a rapid means of obtaining reproducible flow measurements on non-Newtonian fluids by subjecting the sample to definite uniform shear rates, as opposed to the conventional coaxial cylinder viscometer nrhich has the disadvantages of shear rate variations, end effects, and limited range of operation. For use with capillary-type viscometers Goldfinger and Greatbatch (92) devised a photoelectrically triggered timing device to measure the time of flow of a definite volume of liquid through the capillary. Magnetic Resonance. Three papers, a t least, deserve attention for dealing n i t h the potentialities of nuclear magnetic resonance (NMR) and other magnetic techniques as tools in quantitative analysis. Two of these (4$, 218) deal with the use of NMR in moisture determination. The technique is nondestructive, rapid, and accurate, and can be readily conducted by nontechnical personnel. A variety of hygroscopic solids, and particularly starch, have been studied for applications of this technique. Branch (24) has written a review covering microwave spectroscopy, paramagnetic resonance absorption, nuclear magnetic resonance absorption, and quadrupole coupling, and evaluated each as a new method of analysis. Thermometry. Analytical applications of a differential, thermal analysis (DTA) apparatus have been described by Garn and Flaschen (80). I n addition to its normal use in determining temperatures of phase transformations, this technique has proved useful as a control tool in comparing similar, but not identical materials. A new book on differential thermal analysis by Smothers and Chiang (235) should prove useful to analytical chemists. Williams and coworkers (281) have devised a versatile, differential thermal analysis apparatus for obtaining heating and cooling data. This is accomplished by using a vertical, heavy-n.alled metal tube having a constant reproducible temperature gradient along its length. The sample holder is pulled in either direction through this tube a t rates producing desired temperature changes, Morita (187) has used DT-4 in studying dehydration-hydration processes in polyglucosans. Sinions (233) obtained more accurate extrapolation to freezing points in a newly designed, automatic, recording cryoscopic apparatus utilizing a thermistor as the temperature-sensitive element. The unique feature was automatic control of supercooling. Zeffert and Witherspoon (290) have described
a temperature recorder based on thermistors, covering the range from -80" to 32" C. with an accuracy of 0.05" C. A recording of temperature within each range of 12" C. is linear. Krupp and Letschert (143) described a new apparatus which measures the thermal gradients occurring in the reaction between nitrating acids and benzene, thus continuously determining the nitrating capacity of the acids. Two papers on recording gas calorimeters have appeared. Eiseman and Potter (63) evaluated the accuracy of the Cutler-Hammer recording gas calorimeter nhen used nith gases of high heating value. The calorimeter described by Kittig and Bohm (284) automatically drops specimens into a temperature bath and is well suited for a series of measurements. They determined the specific heat of silver between 455' and 852 O K. Titrimetry. Perhaps the greatest activity in automatic analysis, outside of spectrophotometry, has centered on the development, use, and improvement of automatic titration apparatus. Several papers have reviewed applications in plants for specific purposes, such as the determination of phosphorus in fertilizers and of sulfur in steel, and in the general work of an analytical laboratory (21, 32, 36, 75, 105, 191). Duggan and Stevens (55) have described an interesting universal titration console which provides for ordinary pH titrations and other titrations a t constant pH. It permits rapid accumulation of corrected titration data, the use of small sample volumes, and the automatic recording of titrations under specified conditions of mixing, buret delivery, and constant temperature. Simon and Heilbronner (231, 232) have described an autoniatic microtitration unit intended for organic compounds. This determines the apparent dissociation constants of aqueous and nonaqueous solutions on 0.5-mg. samples. Up to 12 titrations may be performed in automatically controlled sequence. Automatic titrations of microamounts of chloride by convection amperometry have been described by Juliard (131). This method determined chloride in the range from 50 to 100 y in 30 ml. of solution. Unger and Herzog (261) described modifications to the Beckman Aquameter to improve precision and flexibility of operation. An automatic titrator for use with constant-current potentiometric titrations was described by Shain and Huber (289). Termination of the titrant flow is based on the shape of the titration curve, and applications to ferrous, manganous, thiosulfate, and chloride ions were described. Lee and Adams (150) combined coulometric and potentiometric titrations by using a device with controlled current. They obtained good results VOL. 31, NO. 4, APRIL 1959
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in the titration of 40 to 200 y of arsenic with bromine. Liberti (153) found that coulometry was an excellent procedure for identification and quantitative determination of the components of an organic mixture separated by gas chromatography. He described a millicoulometer which could be used for either manual or automatic titration, The eluted components were absorbed in a suitable solution n-here they were continuously titrated by an electrolytically generated reagent. Photometric, amperometric, and potentiometric end points were used for compounds including volatile acids, bases, mercaptans, and aldehydes. The procedure can be extended to all organic vapors by burning them a t the end of the column, thus converting them into carbon dioxide to be titrated coulometrically. Said (2B) described continuous and semicontinuous sampling titrations for studying cases where the end point is not sharp or the rate of reaction is not fast enough. Hart (10s) mentioned a continuous titrator controller for use in chemical process slurries including dilution in an exact, but adjustable ratio. Spectrophotometric titration devices have also seen wide development, Chalmers and Walley (33) described an apparatus for the determination of end points from an automatic recording of the rate of change of absorbance of the solution being titrated. This apparatus was found useful for the titration of very dilute solutions and small amounts of more concentrated solutions. Malmstadt and Vassal0 (171) devised a convenient and compact derivative spectrophotometric titrator for automatically performing a wide variety of wellknown color-indicator titrations, without any procedure modifications and with few pretitration considerations or instrument adjustments. Sweet and Zehner (249) described a unique circulation-type apparatus for spectrophotometric titrations. Applications of spectrophotometric titrations have been described in detail for titanium (170), and for fluoride, sulfate, uranium, and thorium (178). High-frequency titrations and equipment to accomplish them have been the subject of considerable attention. One (112) described a high frequency titration apparatus for measurements on a wide range of solutions, while Lane (147) constructed a high-frequency titrator operating a t 250 megacycles per second. Examples were given for its use in conventional as &-ell as in complexometric titrations and in a number of new analytical procedures. Johnson and Timnick (128) have evaluated the performance of a wide range of highfrequency titration apparatus, modified to respond only to changes in the solution conductivity, by replacing the multiturn coil with a single-turn loop,
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achieving a high sensitivity with aqueous sodium chloride solutions having ranges between 0.003 and 5.OM. Square wave titrimetry involving a square wave alternating signal a t constant current or voltage amplitude applied to a pair of microelectrodes has been described by Laitinen and Hall (146). Applications to redox, precipitation, and complexation reactions were described. Jordan and Alleman (130) have designated “enthalpy titrations” for titrimetric methods depending on heats of reaction. The change in temperature in an adiabatic system during the titration is recorded by means of a high-sensitivity thermistor bridge circuit, potentiometer, and a synchronously coupled constant-flow buret. These titrations gave an accurate evaluation of the heats of chelation of divalent cations with EDTA. Malmstadt (169) has described a useful, automatic stopcock twister which opens and closes, with rapid and powerful strokes both lubricated glass stopcocks or those made out of Teflon poly(tetrafluoroethylene) resin. Emissimetry. Mitteldorf (184) has stated that field emission spectrochemical analysis is again in demand and he has surveyed new possibilities for emission spectrochemical analysis. There are still many shortcomings, which are rapidly being overcome. Kemp (136) has revieTed instruments which are commercially available and assure the success of direct-reading optical and x-ray emission techniques in providing high speed analyses on a routine basis. Hunemorder and Hess (118) have described a rapid spectrographic method for the determination of several rare earth elements and thorium in magnesium, using a photoelectric recording spectrometer. Fluorescence is the basis of several alarms and analyzers for nerve gas vapor detection as described by Cherry et al. (38). Indole in a buffered solution serves as the sensitive reagent, reacting to form the fluorescing indoxyl. Infrared Absorptiometry. Increasingly wide attention has been given to the potentialities and advantages of infrared methods of analysis. Among the many general reviens may be mentioned those by Quarendon (208), Troy (260), and Rall (264). Troy considered the fundamentals of infrared and its typical applications to plant stream problems. Hausdorff (106) discussed the various types of infrared continuous analyzers and their applications, as did Maley (165). Maley (166) also gave a useful step by step check list for preventive maintenance and sources of error in continuous infrared analyzers. Discussions dealing with gas analysis by infrared include those by Hartz (104) and by Liston and coworkers (155), who describe important, new
nondispersive positive type analyzers which use a differential principle to compensate for sample cell corrosion and dirt accumulation as well as for overlapping spectra. Maley (167) also built an infrared analyzer combining the advantages of negative filtering with the selectivity and sensitivity of positive pneumatic detection. Martin et al. (174) described some modern forms of the Luft-type infrared gas analyzer involving fixed wave length models employing either diffraction gratings or interference filters. Grundy (98) employed a commercial infrared gas analyzer to measure the rate of evolution of carbon monoxide obtained from the decomposition of pivaloyl chloride by aluminum chloride. This method was more accurate than the titration procedure used earlier. It also was more flexible, thus facilitating rapid and consistent measurements over a wider concentration range. Telling and coworkers (253) reviewed methods of continuous infrared analysis for carbon dioxide. Kood (285) utilized an infrared hygrometer, comprising two narrow bands of infrared radiation, which traverse a 12-inch path through a sample atmosphere containing the humidity concentration to be measured. Roberts (217) outlined recent advances in optical and semiconductor research which should lead to wider use of new types of optical components and radiation detectors in infrared spectrometers. His suggestions apply to the design of high resolution laboratory spectrometers and industrial process control instruments. Brackett (22) obtained linear frequency or wave length scales for several choices of prismatic dispersion by substituting commerically available cams for the existing tangent screw drive on Perkin-Elmer instruments. Meakins (1’77) and Stitt and Bailey (243) have suggested means of auxiliary recording or copying of infrared spectra. Light Absorptiometry. Colorimetry is proving useful in process control, as well as in the continuous monitoring of laboratory operations. Smith and collaborators (234) and Glasser (88, 89) have reviewed new developments in chemical continuous analyzers by optical methods. Dudenbostel and Priestley (64) have discussed process control by flow colorimetry, while Solomon and Caton (836) have described a recording colorimeter for microchemical determinations designed to make rapid and accurate determinations of light absorption in samples containing 30 cu. mm. of fluid. It consists of a point light source, an alternating current modulated detector and modifier, and a servo recorder Stark et aE. (240)devised a means for monitoring absorbance of column elu-
ates in a spectrophotometer. Theiler (254) described a new photometer for controlling industrial processes. Champlin and Dunning (54) and Kruse (144) have described unique means of adding automatic wave length markers to spectrophotometers not normally supplied with them. Spackman, Stein, and Moore (287) determined amino acids in an instrument which rccords the ninhydrin color value of the effluent from ion exchange columns. Gates (81) described an automatic recording saccharimeter having many applications in the sugar and food industries. Helwig and Gordon (108) devised a colorimetric method for continuous recording of atmospheric sulfur dioxide, involving automatic sampling and direct recording of the red-violet color produced with an acidic solution of pararosaniline hydrochloride having limits of detection below 5 p.p.m. Two papers have concerned the determination of nitrogen oxides in air (126, 257). A portable instrument for the rapid detection and recording of 1to 100-micron particle content in atmospheres n-as described by Morrison (188). Dust is collected by impingement on a moving ribbon of acetate film and the absorbance is measured and recorded. Ultraviolet and X-Ray Absorptiometry. Glasaer (86) has described the applications and fundamentals of various types of photometric stream analyzers, stressing the ultraviolet analyzers, the basics of operation, comniercially available instruments, and how to achieve selectivity and sensitivity. A table lists the materials which cannot be detected with ultraviolet and whose presence in the sample do not constitute interferences. Drake (53) has described an ultraviolet scanner camera for use in paper chromatography. Renzetti (212) used a 3oO-foot air sample to measure extremely low concentrations of ozone in the atmosphere. Cherrier’s patent (37) described the use of ultrayiolet to determine sulfur dioxide. h’ishigaki (200) devised an apparatus for a linearly moving x-ray continuous analysis, while Connally (42) reviewed instrumental methods of y-ray spectrometry and its application to the rapid analysis of mixtures of gamma-emitting radioisotopes. Thermoconductimetry. A number of new applications with improved instrumentation in thermal conductivity measurements have been published during the past two years. Burlant and Cannon (29) have described a method for the determination of ozone by thermal conductivity. Heseltine and coworkers (110) have described a simple thermal conductivity meter for gas analysis, with emphasis on
fumigation problems. Kelsen and Eggertsen (198) utilized thermal conductivity for adsorption measurements by a continuous flow method in the determination of surface area. By passing a known amount of nitrogen through the sample, and continuously monitoring the effluent, they obtained results which compared favorably with the pressure-volume procedure. Felton and Buehler (68) are among many who have devised modifications to thermal conductivity cells for use with gas chromatographic columns. This paper describes a high temperature cell intended for use with materials n-hich would otherwise condense a t temperatures ordinarily used in gas chromatography detectors. Refractometry. Increasing application to process stream analysis of techniques involving refractive index measurement is evident from a number of papers published primarily by Glasser and by Fraade. Glassser (87, 90) has covered differential and criticalangle refractometers, and their accuracy and application, including a useful review of commercially available process-stream refractometers. Fraade (72-74) has described the building of a refractometer system from standard components, with application to various processes. It involved an electromechanical positional system following a simple optical effect, which enabled reliable process monitoring as well as continuous control. hiagee and Crain (162) described a rapid-response microwave hygrometer for continuously recording water vapor pressure of atmospheric air. The principle involved the measurement of the contribution of water vapor to the refractive index of atmospheric air through the use of a cavity resonator. Grunwald and Berkowitz (99) utilized interferometer measurements as sensitive means of determining compositions of two-component liquid mixtures. The zero order fringe was identified through the use of a tungsten light source and two auxiliary monochromatic sources. Kapany and Pike (132) devised a photorefractometer to determine slight changes in the refractive index of a liquid. Their instrument was based on the principle that the energy transmitted by total internal reflections through a long dielectric cylinder immersed in a specimen liquid, having an axial light cone condensed a t one end, depends primarily on the difference of refractive index of the rod and its surroundings. Thus by measuring the light emerging from the end of the immersed rod, a sensitive means of measuring small composition changes was devised. They also claimed the possibility of measuring the low refractive index liquids through the use of a hollow rod refractometer. Winogradoff
and Bisset (283) designed a simple, continuously recording instrument capable of measuring retardations down to the order of 10-8 em. Based on the photoelectric measurement of the intensity of light transmitted by two crossed rotating Polaroids, when an oriented film of high polymer exhibiting optical anisotropy is placed between them, the instrument produced intensities related to the birefringences of the sample for light vibrating in three mutually perpendicular directions. These three birefringences could then be used to specify physical properties as well as miscellaneous effects such as sorption, desorption, annealing, and stretching processes on the molecular configuration. Reflectometry. Several new papers involved with determination of the reflection of light from papers impregnated with color producing reagents have been described recently. Kuhns and collaborators (145) described two boron hydride monitoring devices, both of which were designed to make use of nonspecific reduction of triphenyl tetrazolium chloride by boron hydrides, thus producing the red formazan. Sensitivities as low as 0.1 p.p.m. of decaborane and pentaborane were effected. Young, Parsons, and Reeber (288) developed a portable, automatic alarm for detection of toxic agents in the atmosphere. The reaction involved formation of a colored compound when the gas reacted with dianisidine and sodium pyrophosphate peroxide. Conductometry. Garn and Flaschen (79) detected polymorphic phase transformations by continuous measurement of electric resistance. As the sample was heated or cooled through a transition region, significant resistance changes were observed, and the method was found useful as a supplement to differential thermal analysis, especially a t lower temperatures. Johansson, Norman, and Karrman (127) enhanced the reversed phase chromatographic separation of bile acids by using a highfrequency technique for recording the presence of substances in effluents from the column. They measured the conductivity of the eluent as it passed through an external cell and found the technique applicable where solvents with low conductivity are used. Potentiometry. The obvious use of the measurement of electrical potential for measuring pH has continued to receive attention. Gauchat (82) has reviewed industrial applications of potentiometry, giving fundamental consideration to the many difficulties encountered, and analyzing them as guides for developing and assessing practical instrumentation requirements. Feldman (67) has commented on the use and abuse of p H measurements, discussing in some detail VOL. 31, NO. 4, APRIL 1959
651
the liquid junction potential problem. He emphasized that anything which affects the mobilities of the charged particles can affect the magnitude of this error. Only the user can judge whether it can be neglected. He advised that under some conditions the p H meter reading must be considered as simply a reproducible reference point having little or no theoretical significance and that under some conditions the meter reading cannot even be considered as a reproducible reference point. In addition to the pH, the magnitude of the junction potential error depends on ionic strength, nature of the solutes, nature of solvent, presence of colloids, and temperature. The paper by Kahn and Koyama (101) was typical of many reports describing industrial type flow cells for measuring pH, emphasizing proper choice of materials of construction, and details of design. At least two approaches to measuring carbon dioxide have been described recently. Gerts and Loeschcke (84) have modified a glass electrode by covering it with a polyethylene envelope in such a way that only a capillary slit remains between the electrode and the envelope which is filled with 0.001M sodium hydrogen carbonate solution. The polyethylene membrane, being readily permeable to carbon dioxide and difficultly permeable to water and dissolved substances (except for hydrogen ions), then causes the carbon dioxide pressure to equilibrate between the solution under investigation and the bicarbonate buffer without any loss of carbon dioxide. Toren and Heinrich (259) determined carbon dioxide, in the range from 1 p.p.m. to loo%, in a gas stream by passing the gas through a saturated solution of an alkaline earth carbonate containing excess solid, and then measuring the resulting pH. At equilibrium, the p H of the solution is determined by the carbon dioxide content of the gas phase. Strange (245) developed an instrument for the continuous potentiometric determination of hydrogen sulfide or hydrogen cyanide in gas streams by absorbing the gas in an alkaline liquid and determining the potential in a cell containing a vibrating silver electrode and a saturated calomel reference. At least two other interesting papers involving solid electrodes have appeared. Adams and Voorhies (1) described voltammetry a t controlled current, utilizing a three-electrode system and obtaining polarograms essentially free of I R distortion. They recommended the technique as a valid approach to high-resistance polarography. Baumann and Shain (14) found that rotating gold microelectrodes behave in many ways, similarly to platinum electrodes but display certain advan-
652
ANALYTICAL CHEMISTRY
tages such as resistance to oxidation in the absence of complexing anions. Currentimetry. Coulometry, polarography, and mass spectrometry have all been active fields during the past two years. Valuable reviews by Swift (250) and by Lingane (154) have appeared. Merritt et al. (179) have devised an apparatus for automatic controlled-potential electrolysis using an electronic coulometer. This instrument is capable of performing electrolytic oxidations or reductions a t controlled working electrode potentials, with automatic registration of the number of coulombs required. A capacitor served as a sort of integrator such that the time in which a constant current was applied mas the measured variable. Booman (18) integrated electrolysis currents using an instrument with a simple potentiostat circuit with 600ma. capacity. A number of significant applications involving coulometry have appeared. Farrar and coworkers (66) determined uranium and copper in homogeneous reactor fuels, while Sundberg et al. (247) used an automatic coulometric titration procedure for the determination of halides in organic compounds. Miller and DeFord (181) measured the electric current required to produce hydrogen in a generating apparatus for semimicrohydrogenations used in the determination of a wide variety of unsaturated functional groups. Morgan (186) constructed a precision transient current measuring device by means of an electronic current integrator for studying the currents flowing a t a stationary platinum electrode. Rebertus and collaborators (210) found continuous polarographic analysis useful in the analysis of ion exchange effluents and described the determination of nickel, manganese, cobalt, and copper, after mixing with a suitable electrolyte and deoxygenating in a specially designed cell. Blaedel and Todd (16) described other means of continuous deaeration of ion exchange column effluents prior to polarographic measurement. Their applications included cadmium, copper, lead, and fumaric and maleic acids. Sari-yer et al. (227) devised a compact and versatile polarograph utilizing an X-Y recorder for the direct measurement of the electrode potential or applied voltage and a third electrode providing for automatic correction of the I R drop in the cell, hence presenting the record in a convenient and easily catalogued form. Kelley and Fisher (156) described instrumental methods of derivative polarography which used a dropping mercury electrode apparatus having a combination of a diode filter with a parallel T filter. The latter is of particular value for use in very dilute solutions.
Valenta (262) described an apparatus for automatically recording the total polarographic curve of the investigated material with adjustable initial to end voltage. These papers describing the measurement of oxygen concentrations have significance. Brackett and coworkers (23) found the square-wave method useful, while Kreuzer and Nessler (142) described means of in vivo continuous recording of oxygen tension in blood, and Wall (266) reviewed in general the development of a trace oxygen analyzer for plant use. Applications of mass spectrometers in process control (263, 265) and in vacuum research (61) have appeared. Edwards (61) particularly emphasized certain new types of mass spectrometers and attempted to assess their potentialities. Gentry (85) discussrd the line recorder mass spectrometer as an analytical instrument. Dielectrimetry. Fisher and coworkers (70) have discussed radiofrequency analyzers for laboratory and plant work, emphasizing the outstanding advantage that no electrodes need be in contact with the solutions. Thomas and Beaugh (265) and Wall (268) described continuous monitors involving measurement of dielectric constants, examples including the measurement of octanes in catalytic roforming units and propane oil ratios in dewaxing units in petroleum refineries. Radioactimetry. Gillespie and Zedler (85) have discussed continuous water monitors for radioactive wastes, while Allen (8) has reviewed the instrumental tools for radioisotope tracers which have been used successfully to solve a variety of problems in petroleum, textile, and other fields. Deal, Otvos, Smith, and Zucco (48) have devised a radiological detector for gas chromatography which uses differences in P ionization cross sections, thus producing an instrument of very rapid responsr, high stability, high sensitivity, and broad applicability and having thc added advantage of being insensitive to gas flow rate. Russell and Leng (219) have developed a quartz-fiber optical system and electronic circuits to increase the range and accuracy of ionization current measurements involved in automatic quartz-fiber electrometers. DATA
An impressive choice of “aids” is becoming available t o the analytical chemist in dealing with his everincreasing problems of data collection, assimilation, storage, and retrieval. A survey of recorders (124) contains tables giving characteristics of various. commercial models. Rutledge (220, 621) has described in some detail ap-
plications of the recording potentiometer, while Pihl (2006) dealt with evaluation factors for recorders, having made comparisons based on resolving power, time factors, and operational cost. Moyer (190) considered the following factors in selecting a recording galvanometer: frequency response, sensitivity, phase angle, damping, and power dissipation. Tn7o authors, Moseley (189) and Sadler (222) have considered the advantages and characteristics of X-Y recorders. For data already obtained, or obtained point-by-point, several authors have described useful data- or curveplotting devices. Muller and Lonadier (193) used a multipoint print-out recorder and a sliding translatory potentiometer together with a few accessories such as a data-plotting apparatus. Through circuit modifications, other functions such as squaring, square root extraction, finding logs, or plotting hyperbolas could be performed. Riblet (214) claimed a 60 to 1 saving in manhours through the use of a device that automatically plots data, primarily telemetered, as the function versus real time. Stevens and Duggan (242) achieved semiautomatic subtraction of titration curves through the use of a simple, but versatile curve-plotting device employing a slide wire for converting distances into direct current voltages, eliminating all numerical records and producing the corrected titration curve plotted point by point on a chart recorder. Data reduction through the use of either special or general purpose computers is becoming recognized as an important tool in many problems. Laws (149) has described the objective of a process data reduction system as the measurement of process variables and the rapid recording of these measurements in digital form. Gaillard has treated the problem (77) of the automatic reading and analysis of charts having already registered recorder curves. Books on computers are almost obsolete the day after they are printed, but a number, among them the one by Livesley (157) merit the attention of analytical chemists. McCracken (159) has given an excellent resume of applications of computers to the work of the analyst. Dyroff and Steidler (59) have described how a computer can simulate analytical laboratory operations. Through the use of a card-programmed calculator, the simulation of an entire year’s work was achieved in 15 minutes. This enabled the determination of the optimum man power for the laboratory to meet any specified deadline a t minimum cost. More specific applications may be found in such papers as those by Anderson and Moser (9)’ describing the use of a computer to convert emission
spectrographic film line transmittances into element concentrations in samples. I n addition to computing assay precision, McAdams (158) described the semiautomatic assembly of mass spectrometry matrices, using a medium sized digital computer and calibration data from a mass spectrometer assembled into a direct matrix in a form suitable for mathematic inversion. The setup allowed for corrections to be made for impurity components and for changes in instrument sensitivity. The National Bureau of Standards (196) has recently described automatic equipment which provides immediate statistical analysis of spectrometric data. White and MacAdam (279) constructed an electronic, digital tristimulus integrator with interchangeable punched-tape programs corresponding to different illuminants or receptors, including visual presentation of the tristimulus values. Roberts and Pizer (216) described an improved adherometer, including an electronic integrating device that yields an average value of the force usually measured. Information storage and retrieval are receiving belated attention. Spencer and Johnson (238) have described a method whereby standard punched cards may be used for the storage of gas chromatographic data to be available for storage, exchange, or construction of charts and tables. The h’ational Bureau of Standards has announced (195) a Microcite reference system, a method to render index information directly accessible and reproducible in order to increase the effectiveness of literature searching. The initial use was proposed for the Bureau’s instrumentation reference service and consists of photographically storing reduced copies of abstracts so that they can be readily located and read. Addison et al. ( 2 ) have devoted some attention to analytical laboratory operations and controls through the use of business machine punched card procedures t o aid laboratories in keeping track of samples and recording and reporting results of analyses. Miscellaneous. Sonic gas analyzers continue t o receive some attentione.g., Martin’s patent (173) and special models for 0 to 10% carbon dioxide (944) and low concentrations of gases in air (213). Particle counters useful for obtaining size distributions, etc., have been further developed by Kassenstein (194), Clarke and Ellenbogen (do), and Parker and Horst (203).
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(252) Taylof, W. S., Moyer, G. G., “Electronic Instruments for the Food 1R58 Industry,” ISA Conference, September 1958. (212) Renzetti, N.A., ANAL.CHEM.29, (253) Telling, R. C., Elsworth, R., East 869 11957). D. N.. J . A *m- l . Bacteriol. 21 (No. 1),26, (213)Rev. dci. Znstr. 28,217 (1957). (i958j. (214)Riblet, H. B., Electronics 30 (No. 8), (254)Theiler, C. R., Brit. Chem. Eng. 182 (1957). 3,266 (1958). (215)Riggle, G. C., Crisp, L. R., ANAL. (255) Thomas, B. W.,Beaugh, J. B., CHEX28,1799(1956). Petrol. Refiner 35 (No. lo), 133 (1956). (216)Roberts, A. G., Pizer, R. S., ASTM (256) Thomas, M. D., Znd. Eng. Chem. Bull. 1957(To. 221),53. 48,1522 (1956). (217)Roberts, D. H.,Chem. & Znd. (257)Thomas, hI. D., MacLeod, J. A., (London)1957,482. Robbins, R. C., Goettelman, R. C., (218) Rubin, H., ZSA Journal 5 ( S o . l), Eldridge, R. W., Rogers, L. H., ANAL. 64 (1958). CHEM.28,1810(1956). (2l-9)Russell, hf. C. B., Leng, J., J . Sci. (258)Thomson, J., J . Sci. 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J., Chiang, Y., ( 2 7 7 ) Zbid., p. 61. “Differential Thermal Analysis: Theory (278)White, T. T., Campanile, V. A., and Practice,” Chemical Pub. Co., Agazzi, E. J., TeSelle, L. D., Tait, New York, 1958. P. C., Brooks, F. R., Peters, E. D., (236) Solomon, A. K.,Caton, D. C., Zbid., 30,409(1958). AN.4L. CHEX 30,291(1958). (279)White, W.E.,MacAdam, D. L., (237)Spackman, D. H., Stein, W. H., J . O p t . SOC. Am. 47,605(1957). Moore, S., Zbid., 30,1190 (1958). (280) Willard, H. H., Merritt, L. L., Jr., (238)Spencer, C. F.,Johnson, J. F., Dean, J. A., “Instrumental Methods of Zbid., 30,893(1958). Analysis,” 3rd ed., Van Nostrand, (239)Spracklen, S. B.,I S A Journal 4, Sew York, 1958. 514 (1957). (281) Williams, D.D., Barefoot, R. D., (240) Stark, J. B., Teranishi, R., Bailey, Miller, R. R., ANAL. CHEM.30, 492 G. F., ANAL.CHEM.29,861 (1957). (241)Stephenson, J. L.,Smith, G. W., (1958). (282) Wingo, W. J., Zbid., 30, 1710 Tranthan, H. V., Rev. Sci. Instr. 28,381 (1957). (1958). 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R., Zehner, J., ANAL. (1958). CHEY.30,1713 (1958). (2503 Swift. E. H.. Ibid... 28. , 1804 (289)Young. J. R.. Chem. & Ind. (London) ’ (1956). ’ . 19S8,1111: (290) Zeffert, B.M., Witherspoon, R. R., (251) Talley, E. A., Fitzpatrick, T. J., A N A L . CHEM. 28,1701 (1956). Zbid., 29,988(1957). of Electronic Equipment in the Nuclear Industry,” IS.4 Conference, September ---I.
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