carbonate is readily accomplished. Since propylene carbonate is more dense than water, the tedium of extractions using solvents lighter than water is avoided and multiple extractions tend to cancel factors affecting the distribution coefficient in single extraction systems. The interferences due to mercury, zinc, and cobalt occur because these metals form extractable species with thiocyanate and hinder the extraction of the copper(I1)-thiocyanate complex ion. However, more than 14.5 mg per 50 ml of sample of these metals can be accommodated with little effect on the accuracy of the method.
Table 111. Determination of Copper in NBS Standard Samples S B S Sample 19G S t e e l
h B S Sample Y5B Aluminum Allo) Sariple
\liquor
-.Cua
Sample
Aliquot
1
1
0.090
2 3 4
1 1 1 1
1
1 1 1
2 3 4
2 2 2 2
2 3
3 -97 3.98 4.08 4.17 3.93 3.99
0.092 0.092 0.094 0.094 0,090 0.093
1
4
4.05 4.09
2 2 2 2
AV = 4.03
1 2 3 4
0:
cub
LITERATURE C I T E D
0.093
(1) C. E. Mulford, At. Absorp. News/., 5, 88 (1966). (2) B. G. Stephens and H. A. Suddeth, Anal. Chem., 39, 1478 (1967). (3) "Propylene Carbonate Technical Bulletin," Jefferson Chemical Co., Houston, Texas, 1960. (4) R . F. Nelson and R. N. Adams, J. Necfroanal. Chem., 13, 184 (1967). (5) 6. G. Stephens, J. C. Loftin, W. C. Looney, and K. A. Williams, Analyst (London). 96, 230 (1971). (6) R . J. Jakubiec and D.F. Boltz, Mlkrochim. Acta. 1199 (1970). (7) K. Murata and S.Ikeda. J. lnoro. Nucl. Chem.. 32. 267 (1970) (8) B. G. Stephens, H. L. Felkel. :r., and W. M. S p h , Anal 'Chem., 48, 692 (1974). (9) J. E. Allan, Spectrochlm. Acta, 17, 459 (1961). (IO) D.C. Munro, Appl. Specfrosc., 22, 199 (1966). (11) P. G. Stecher, Ed., "The Merck Index," 8th ed., Merck 8 Co., Inc., Rahway, N.J., 1968, p 590. (12) James C. Loftin, Wofford College, Spartanburg, S.C.,personal communication, 1973.
AV = 0.092
a NBS analyses: reported, :?1.99%; average, 3.9970; range, 3.97%4.0370. NBS analyses: reported, 0.093%; average, 0.093%; range, 0.089%-0.100%.
is used as a masking agent, a t least 112 mg of iron per 50 ml of aqueous phase can be tolerated. The results are shown in Table 111. CONCLUSION
RECEIVEDfor review December 9, 1974. Accepted April 24,
The determination of copper by atomic absorption after its extraction as the thiocyanate complex into propylene
1975.
New Zeeman Method for Atomic Absorption Spectrophotometry Hideaki Koizumi and Kazuo Yasuda Naka Works Hifachi Ltd. Katsufa, Ibaraki, Japan
Because of the importance in environmental research, it is highly desirable to develop a simple instrument which enables one to determine accurately trace elements in foods, living materials, and atmosphere in a short time. Recently, T. Hadeishi et al. have proposed a new technique for the detection of mercury in which the hyperfine structure of Ig9Hg has been used as the light source of atomic absorption spectrophotometry ( I ) . Furthermore, Hadeishi has introduced a significant improvement of the technique by using the isotope effect ( 2 ) . The magnetic field of about 7 kgauss was applied to the light source in the direction of the propagation of the light beam, and circularly polarized Zeeman components u+ and u -of lgSHg were used as reference and absorbing light, respectively. In the latest work, Hadeishi et al. used H and u* components of *04Hg as the absorbing and the reference light respectively ( 3 ) .These methods developed by them are far superior in background correction to the conventional methods. However, it is difficult to apply their techniques to the determination of various elements because the special isotope should be used for the light source. In the present article, we report the Zeeman method for atomic absorption spectrophotometry in which the magnetic field is applied to the light source of natural mercury in the direction perpendicular to the propagation of the light beam, and the Zeeman components are used as a reference and an absorbing light. By studying profiles of the absorption and the emission line of natural mercury, the following results were obtained; The magnetic field of 15
kgauss is sufficient to shift the u* components of the natural mercury lamp from the absorption line because the width of the absorption line is smaller than 23 GHz and the hyperfine splittings of natural mercury light source at this field are smaller than the absorption line width. Therefore, it is possible to use the H and u* components a t 15 kgauss as an absorbing and a reference light, respectively. A very simple atomic absorption spectrophotometer was constructed by using the linearly polarized Zeeman components of a natural mercury lamp as the light source. The detection of trace mercury of about 70 picograms could be achieved in 1 minute. Because it is unnecessary to use the special isotope, the present method is widely applicable for the detection of various elements such as Cd, Pb, Cu, Zn, Cr, and Al, as will be reported elsewhere. I t should be emphasized that, according to our method, chemical pretreatment is unnecessary for a quantitative analysis for mercury. When we observed emission spectra of mercury in a magnetic field transverse to the direction of the light source, the spectral line splits into three components which correspond to transitions of AM = 0, AM = fl,Le., H and u* components. Whereas the H line is linearly polarized and parallel to the magnetic field, the uc and u- lines are linearly polarized and perpendicular to the magnetic field. The intensity of the H line is equal to that of u* lines, if self-absorption of each line does not take place in the light source. When the magnetic field of larger than 15 kgauss is applied to the light source, only the wavelength of H com-
ANALYTICAL CHEMISTRY, VOL. 47,
NO. 9, AUGUST 1975
1679
Direct output
Preamp. Log. convertor
-
. ? .
Lock-in amp.
-s o
Integrated output
v
Resonance absorption by m e r c u r y
0,
integrator --c)
2 +.c
E Reference
!
Natural mercury lamp
generator
?!
50
I-
A
I
100
0 (100 MHz)
7r
Magnet
50
Furnace (
Resonance a b s o r p t i o n by m e r c u r y
90O0C)
Figure 1. Schematic diagram of the experimental apparatus ,_---
I-
___---_/' ponent coincides with that of an absorption line of mercury, even if the Doppler and pressure effects give rise to the line broadening or frequency shift. Hence, it is possible to use the T component as the light source for absorption and the u+ and u- as reference. When the light beams consisting of the three components pass through an absorption cell, the x component is absorbed not only by the mercury atom but also by any other molecules which have resonant levels with the incident light. The x component is also scattered by the pre-atomized mist. Although the u+ and crcomponents are not absorbed by the mercury in the sample cell, they could be absorbed or scattered by a combustion product or a mist. The intensity of light beams can be approximately expressed as follows,
I , = I,, exp ( - c Y ( ~ A K A +,~ B K ) }~ ,
(1)
+
I,* = I,,* exp (-a(nAKA,* TZBK~,,*)) (2) Here, K A Tand KB, are the coefficient of atomic absorption and background absorption of the T component, respectively. KA,+ and KBu+are those for the u+ and u- components, n~ and n~ are the number of mercury atoms and apparent number of background absorbers, CY is a constant, and I,, and I,,* are incident intensities of absorbing and reference lights, respectively. I,, is equal to I,,*. KB, and KBu*are approximately equal, because the differences of wavelength between the T and u* lines are extremely small compared with the absorption band of molecules. The following relation is obtained from Equations 1 and 2. log I , - log I,* = - a n ~ ( K ~ KA,*) , 0: nA (3) And, we can obtain n A , the number of the mercury atom, without any interference from the background absorption. EXPERIMENTAL The schematic diagram of the experimental apparatus is shown in Figure 1. We constructed an electrodeless discharge lamp which contained a small amount of natural mercury and 2 Torr of Ar gas. Electrical energy of about 1 W a t 100 MHz was supplied to the lamp in the tank coil of the oscillator. The tadpole shape lamp consists of a reservoir of mercury and a capillary. It gives rise to a stable and powerful emission in a strong magnetic field. The capillary of the lamp was settled just between the pole pieces of a small per1680
ANALYTICAL CHEMISTRY, VOL. 47, NO. 9, AUGUST 1975
//'
100
0
5
lo Time ( s e c )
Figure 2. Signals of x and u* obtained by using a high speed recorder directly connected with the output of the photomultiplier (A) Sample: solution of mercury, 20 ppm, 10 @I.( B ) Sample: hair, 15 mg (containingabout 5 ppm of mercury)
manent magnet of 2 kg. The magnet produces a homogeneous magnetic field of about 17 kgauss, and has a gap of 4 mm. The reservoir of the lamp was cooled to a constant temperature which is several degrees lower than that of the capillary to keep the vapor pressure constant and to prevent the droplet of mercury from moving in the lamp. The intensity of the Y component was a little different from that of u t , because their self-absorptions were slightly different. Hence, a polarization compensator of thin quartz plates was placed across the light beams to satisfy the condition of I,, = Io,*. An atomization furnace composed of heaters and a T-shaped quartz tube was constructed. The furnace has the dual purpose of absorption and combustion cell, and it is possible to reach a maximum temperature of 1200 "C. Usually, the furnace was kept a t a constant temperature of 900 "C by applying the proportional control technique in which SCR was used. The solid or liquid sample was put in a small quartz cup, and directly inserted into the furnace by the holder. In case of the liquid sample, a small amount of quartz wool was put in the cup to prevent bumping. Then, oxygen, a carrier and combustion gas was flowed through the furnace at a flow rate of about 0.5 l./min. A combustible sample was burned in the furnace within one minute. Mercury contained in the sample was vaporized and sent into the absorption cell together with smoke, the combustion product. The R and the u* components were separated by a rotating linear polarizer after passing through the absorption cell and detected by a photomultiplier alternately. An interference filter for 2537 A was placed in front of the photomultiplier to cut the other lines. The gain of the photomultiplier was automatically controlled so that the reference signal of u* was kept a t a constant level. After that the absorbed and the reference signals were transformed into logarithm, the difference between them was amplified by a lock-in amplifier, and integrated over the time interval when the mercury vapor flowed through the absorption cell.
RESULTS AND DISCUSSION Figure 2 shows the signal obtained by using a high speed recorder directly connected to the output of the photomul-
75
Table I. Measured Result of NBS'Standard Reference Materials Sample
Orchard Leaves (SRM- 1571) Coal (SRM- 1632)
Certified value, Hg, ppm
Hg S P P ~
top
h
Our result, Hg, pprn
m c
Hg 5ppm
Hg
lop1
5ppm
1
op
v
0.155 + 0.015 0.12
+ 0.02
0.153 0.117
+
*
0.014
0.013
tiplier. By rotating the linear polarizer, the signals of x and o* are recorded alternately. The upper and lower points of the track correspond to the absorption of x and u*, respectively. Repetition rate of the signals is 100 Hz. The signal observed in the solution containing 200 ng of mercury changes with time as shown in Figure 2A, which shows that only the x component is absorbed. Figure 2B shows the signal in the case of 15 mg of human hair. The mercury content of the hair is about 5 ppm. Both components are absorbed by the combustion products of hair, but the A component is more strongly absorbed because of the presence of mercury. The signals of x and o* are transformed into logarithm, and their difference is amplified. Benzene and acetone absorb strongly the radiation of 2537 A, Le., the mercury resonance line which is used for the present observation. As the presence of these materials and their combustion products in the sample cell might give rise to ambiguous results of the analysis of mercury, the following experiment was performed to examine the effect. About 10 mg of benzene or acetone was introduced into the furnace, and the signal was observed by the present method. But no output signal could be observed since the absorption of x component was equal to that of u* unless some traces of mercury were present. While the overor underestimations of the background corrections are made frequently in conventional methods ( 4 ) , it is not so in the present method. Furthermore, even when benzene and acetone were added to the mercury solutions, no interference effect was observed in the results by this method of analysis as shown in Figure 3. We have determined the mercury contents in hair, urine, and various compounds by this method. The observed results were in good agreement with those obtained by the conventional method of flameless atomic absorption with chemical pretreatment (5). Furthermore, in order to ascertain the accuracy of our method, mercury contents in NBS Standard samples were also measured. Our result by the present method agreed precisely with the result of NBS, as shown in Table I. About 25-35 mg of the samples were used for our measurements. The instrument was calibrated by standard solution containing 1 pprn of mercury in 0.5N "03 prepared just before the measurement. The NBS samples were kept in an oven a t 90 "C for 24 hours to dry before the measurement. The maximum loading capacity of solid or liquid sample into the furnace varies from about 30 to 100 mg, depending upon the type of the sample, i.e., soil, hair, serum. If the quantity of the sample is more than that, the measurement will be difficult. In such a case, a major portion of the light beam is absorbed or scattered by the smoke even in the oxygen atmosphere, and both the components K and u* of the light can hardly transmit through the smoke. In such cases, however, the combustion speed is reduced by changing the sample position in the furnace. Then, more than some 5% of the light will transmit through the cell although the retention time of the smoke is prolonged. In the case of such samples as oil or butter, which were the most difficult to analyze in our experiment, the samples of 30-40 mg could be analyzed by putting a wick of quartz wool a t the opening of the sample cup. When the technique described
Acetone 1Opl
c
3
a c
Benzene
3.15
1oy.r
Qi
u
c
3 0 -0
? 0
c
n
50
a
2
m
3.10
c
c
a
25
a c
0.05
0 0
0
20
10 Time ( m i n )
Figure 3. The effectiveness of background correction by the present method (The effect of integration is also shown)
above was not used, the maximum loading weight of them was smaller than 10 mg. The absolute detection limit was 70 pg of mercury, and the working curve was linear up to 150 ng of mercury. C.V. value of better than 2% including sampling error was obtained in the case of solution containing 10-150 ng of mercury. The T-shaped furnace consists of two parts, i.e., the combustion and the absorption cell. The signal was integrated over the flow time of the mercury vapor through the absorption cell. Therefore, we could eliminate the apparent interference due to fractional distillation of compounds and the difference of atomization time when we analyzed various samples. If not integrated, the measurement could hardly be calibrated simply by using the standard solution of mercury. Hence, the analytical results would be unsatisfactory, because a number of peaks appear frequently in the signal traces on the chart. The integrated signal gives the exact content of mercury even in the case where the peak value of the signal before integration varies widely under the various conditions of vaporization or combustion. The same sensitivity was obtained a t various furnace temperatures from 850 to 950 "C. By using the high resolution spectrophotometer based upon the magnetic scanning technique with a 204Hglamp (61, we observed the profile of atomic absorption line broadened by the pressure and Doppler effect, Zeeman shifted hyperfine structures of natural mercury, and high resolution molecular absorption spectra in the region of the resonance line. In the magnetic scanning technique, the lamp containing 74% 204Hg,16% 202Hg,and the other isotopes was used instead of the 204Hglight source. The half width of the mercury resonance absorption line at 2537 A was less than 23 GHz a t 1 atm of Ar and at 300 K. The emission line from the light source placed in the magnetic field of 15 kgauss was clearly separated into three components of x and u* even in the case of the source containing natural mercury in 2 Torr of Ar, and it was confirmed that the complex isotope effect and the nuclear spin ANALYTICAL CHEMISTRY, VOL. 47, NO. 9, AUGUST 1975
1681
100
-
h
P v
I
I
I
I
I
5
10
15
20
25
I
Magnetic f i e l d ( k G )
Transmission of the T and u* of components of natural mercury light through a mercury cell with 1 atm of Ar Flgure 4.
effect of mercury are too small to give any difficulty in the procedure of analysis. Figure 4 shows the relation between the magnetic field of the natural mercury light source and the absorption of T and u* of mercury. Almost the same relation as Figure 4 was obtained in the case of the *04Hglight source when the applied magnetic field was larger than 15 kgauss. However, there was a little difference when the field was smaller than 15 kgauss because the line width of 204Hglight source is narrower than the overall width of the natural mercury light source. In order to compare the sensitivities of both
cases, the standard solution containing 50 ng of mercury was analyzed with this instrument using the natural mercury light source and the 204Hglight source in the magnetic field of 15 kgauss. The observed results were 50.0 f 0.3 ng and 50.7 f 0.9 ng, respectively. The result shows that one need not use any particular isotope in the present method. 'We observed the absorption spectra of benzene, acetone and the decomposed vapors of these molecules in the cell. These spectra did not show any fine or hyperfine structures in the neighboring region of 80 GHz of the mercury resonance line at 2537 A. Thus, we may safely conclude that the interference of molecular absorption and scattering of benzene, acetone, and their decomposed vapors have no effect on the accuracy of the measurements. As described above, this method can be applied not only to mercury but also to various other elements.
ACKNOWLEDGMENT We thank T. Hadeishi, K. Ohishi, K. Uchino, K. Seki, S. Mayama, K. Kitagawa, and M. Katayama for their useful suggestions and great help. LITERATURE CITED (1) T. Hadeishi and R. D. McLaughlin, Science (London), 174, 404 (1971). (2) T. Hadeishi, Appl. Phys. Lett., 21, 438 (1972). (3) T. Hadeishi, D. A. Church, R. D. McLaughlin, B. D. Zak, and M. Nakamura, Science (London), in press. (4) 8. V. L'vov, Spectrochim. Acta, Part 6, 24, 53 (1969). (5) W. R. Hatch and W. L. Ott, Anal. Chem., 40, 2085 (1968). (6) F. Bitter, H. Plotkin, B. Richter, A. Teriotdale, and J. E. R. Young, Phys. Rev., 01, 421 (1953).
RECEIVEDfor review December 30, 1974. Accepted April 28, 1975.
Comparison of Atomic Absorption and Neutron Activation Analyses for the Determination of Silver, Chromium, and Zinc in Various Marine Organisms Richard A. Greig Milford Laboratory, Middle Atlantic Coastal Fisheries Center, National Marine Fisheries Service, Milford, Conn. 06460
Investigations are in progress a t this laboratory to determine the abundance and distribution of trace metals in biota collected from coastal marine waters of the middle eastern United States. During the course of this work, there has been the opportunity to obtain comparative data for the analysis of silver, chromium, and zinc by two different techniques-atomic absorption analysis and neutron activation analysis. Data by these two techniques were obtained on marine fish, shellfish, and plankton. This report presents the results of the comparative data obtained by the two techniques named above and also a brief discussion of the significance of the data.
MATERIALS AND METHODS Fish Preparation. Fish tissues and organs were dissected on board research vessels and stored frozen in plastic bags. At the laboratory, the samples were either ground in an electric blender (glass jars, stainless steel blades) and frozen in plastic jars or freeze-dried for 48 hr, then ground with Teflon utensils and stored in plastic vials. Plankton samples were dried a t 105-115 OC for 18-24 hr in glass 1682
ANALYTICAL CHEMISTRY, VOL. 47, NO. 9, AUGUST 1975
beakers; dried samples were ground with Teflon utensils and stored in plastic vials. Samples were split into subsamples for analysis by either atomic absorption or neutron activation analysis as follows: 1) for muscle, the flesh (no skin) was ground in an electric blender; half of it was then saved as frozen material for atomic absorption analysis, while the other half was freeze-dried and ground with Teflon utensils for neutron activation analysis; 2) for all other samples, except gills and plankton, the entire organ was freeze-dried and ground into a powder with Teflon utensils; half of it was then saved for atomic absorption and half for neutron activation analysis. In the case of gills, they were dissected from the bony arch and freeze-dried. Because the dried material could not be ground into a fine powder, the gill filaments were randomly divided into two samples-one for atomic absorption and one for neutron activation analyses. In the case of plankton, the finely ground material was simply split into two subsamples-one for each technique. In all cases, the final ground materials were stored for various periods up to nine months and, in some instances, the storage period prior to analysis differed for atomic absorption vs. neutron activation analysis. No attempt was made, however, to relate storage time with analytical results. Chemical Analyses. Atomic Absorption. A procedure developed at this laboratory was used; parts of this procedure were
