Anal. Chem. 1983, 55, 1064-1067
1064
mechanisms proposed for atomization of this element (2, 4, 7-11). Greater control of this variable as well as the surface activity or age of the graphite substrate (27-29) and purity of the sheath gas will be required if meaningful comparisons of results from different researchers are to be made.
ACKNOWLEDGMENT The authors thank J. A. Holcombe for helpful discussion. Registry No. Pb, 7439-92-1; PbO, 1317-36-8.
LITERATURE CITED (1) Katskov, D. A.; Grlnshtein, I. L. Zh. Prlkl. Spektrosk. 1981, 3 4 , 773-780. (2) L'vov, B. V.; Bayunov, P. A.; Ryabchuk, G. N. Spectruchim. Acta, Part 6 1981, 366, 397-425. (3) L'vov, 8. V.; Katskov, D. A.; Krugllkova, L. P.; Poizik, L. K. Spectrochlm. Acta, Part B 1978, 376, 49-80. (4) Sturgeon, R. E.; Chakrabartl, C. L.; Langford, C. H. Anal. Chem. 1978, 48, 1792-1807. (5) Smets, B. Spectrochim. Acta, Part 6 1880, 3 5 , 33-42. (6) Byrne, J. P. Aust. J . Chem. 1978, 32, 249-255. (7) Genc, 0.;Akman, S.; Ozdural, A. R.; Ates, S.;Balkis, T. Spectrochim. Acta, Part 6 1981, 366, 163-168. (8) Katskov, D. A.; Grlnshteln, I. L.; Krugllkova, L. P. Zh. Prikl. Spektrosk. 1980, 3 3 , 804-812. (9) Katskov, D. A.; L'vov, 8. V.; Polzik, L. K.; Semenov, Yu. V. Zh. Prlkl. Spektrosk. 1977, 26, 598-605. (10) Sedykh, E. M.; Belyaev, Yu. I.;Ozhegov, P. I.Zh. Anal. Khlm. 1979, 34, 1984-1992. (11) Chakrabartl, C. L.; Wan, C. C.; Teskey, R. J.; Chang, S.B.; Hamed, H. A.; Bertels, P. C. Spectrochim. Acta, Part 6 1981, 366, 427-438.
(12) Frech, W.; Zhou, N. G.; Lundberg, E. Spectrochlm.Acta, Part 6 1982, 376, 691-702. (13) L'vov, B. V.; Ryabchuk, G. N. Spectrochim. Acta, Part 6 1982, 376, 673-684. (14) Frech, W.; Cedergren, A. Anal. Chlm. Acta 1980, 113, 227-235. (15) Styris, D. L.; Kaye, J. H. Spectrochlm. Acta, Part 6 1981, 366, 41-47. (16) Styris, D. L.; Kaye, J. H. Anal. Chem. 1982, 5 4 , 864-869. (17) Frech, W.; Cedergren, A. Anal. Chim. Acta 1977, 8 8 , 57-67. (18) Rowston, W. B.; Ottaway, J. M. Analyst (London) 1979, 104, 645-659. (19) Langmulr, I. Phys. Rev. 1913, 2 , 329-347. (20) Bradley, R. S.;Evans, M. G.; Whytlaw-Gray, R. W. Proc. R . SOC. (London), Ser. A 1946, 186A, 368-395. (21) L'vov, B. V. Spectrochim. Acta, Part6 1978, 336, 153-193. (22) Margrave, J. L. Ed. "The Characterization of High Temperature Vapors"; Wiley: New York, 1967. (23) Drowart, J.; Colin, R.; Exsteen, G. Trans. Faraday SOC.1965, 6 1 , 1376-1383. (24) Fiaim, T. A.; Ownby, P. D. J . Vac. Sci. Technoi. 1971, 8 , 861-662. (25) Stafford, F. E. High Temp.-High Pressures 1971, 3 , 213-224. (26) Brewer, L.; Mastlck, D. F. J . Chem. Phys. 1951, 19, 834-841. (27) Holcombe, J. A.; Ekiund, R. H.; Smith, J. E. Anal. Chem. 1979, 5 7 , 1205-1209. (28) Barln, I . ; Knacke, 0. "Thermochemical Properties of Inorganic Substances"; Springer: New York, 1973. (29) Salmon, S. G.; Davis, R. H.; Hoicombe, J. A. Anal. Chem. 1981, 5 3 , 324-330. (30) Salmon, S. G.; Hoicombe, J. A. Anal. Chem. 1982, 5 4 , 630-634. (31) Holcombe, J. A.; Rayson, G. D.; Akerllnd, N. Spectrochim. Acta, Part 6 1982, 376, 319-330.
RECEIVED for review December 3, 1982. Accepted January 31, 1983.
Graphite Furnace Atomic Absorption Spectrometry with Matrix Modification for Determination of Cadmium and Lead in Human Urine Kunnath S. Subramanlan, Jean-Charles Meranger, and Judy E. MacKeen Environmental Health Centre, Health and Welfare Canada, Tunney's Pasture, Ottawa, Ontario K I A OL2, Canada
A diammonlum hydrogen phosphate-nitric acid-graphlte furnace atomlc absorption spectrophotometrlc method and an ammonlum nltrate-nltrlc acid-graphlte furnace atomlc absorptlon spectrophotometrlc procedure have been developed for determlnlng nanogram per millllfter levels of cadmlum and lead, respectlvely, In human urine samples. Values for Cd In the sample are obtalned by direct comparlson to h e a r working curves prepared from aqueous standards In the diammonlum hydrogen phosphate-nltrlc acid medium; there Is no need to use the method of standard addltlon or matrlxmatched callbratlon curves. I n the case of Pb, matrlxmatched calibration plots are essential. The detection limlts (3 standard devlatlons of blank) for Cd and Pb are 0.9 and 4.1 ng/mL, respectlvely. Data are presented on the degree of accuracy and preclslon of the methods. At least 25 samples can be analyzed per hour. The sensltlvlty and slmpllclty of the procedures make them attractlve for routlne envlronmental survelllance Involving large throughput of samples.
The adverse toxic effects of cadmium ( I ) and lead (2) are now well recognized. The accumulation of cadmium in the body has been linked with respiratory ailments, hypertension, and damage to bones, kidney, and liver (1). Lead reportedly
interferes with a number of body functions, notably the central nervous system, the hematopoietic system) and the kidney (2). Some workers (2-4) regard the presence of Cd and P b in urine as an indirect index of the renal and total body burden of these metals. Therefore, determination of Cd and P b in urine is useful for assessing occupational and environmental exposure to these two elements. Several electrothermal atomic absorption methods have been published for Cd (5)and P b (6) in urine. However, the major organic and inorganic species present in urine produce spectral and chemical interference. To overcome the interference, three different approaches have been used: (i) separation of the analyte from the bulk matrix, using either solvent extraction (7-12) or electrodeposition (13); (ii) selective volatilization of the analyte or matrix (14,15); and (iii) matrix modification in which the atomization rate of the analyte is retarded sufficiently to resolve the atomic absorption signal of the analyte from the nonatomic absorption signal of the matrix (16-20). Any procedure involving preconcentration is slow, prone to contamination, and probably subject to incomplete recoveries especially when extraction of raw urine sample is attempted (11). Ross and Gonzalez (14) reported the direct determination of Cd in urine by selectively atomizing the metal from the bulk of the matrix, but Gardiner et al. (21) observed a 30-35% depression of the Cd signals in the directly injected
0003-2700/83/0355-1064$01.50/0 Publlshed 1983 by the Amerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL. 55, NO. 7, JUNE 1983
urine samples. Carmack and Evenson (15) used a temperature-controlled furnace to achieve selective volatilization and molybdenum-coated graphite tubes to reduce matrix interferences, but the low charring (370 "C) and atomization (900 "C) temperatures required may lead t o both poor precision and sensitivity as a result of residue buildup from the incompletely volatilized wine matrix. In an attempt to decrease nonspecific absorption, some authors diluted the urine sample with nitric acid1 (22-24, but the variable nature of the urine matrix necessitated the use of the time-consuming standard addition procedure. Lagesson and Andralsko (16) reported a matrix modification procedure involving ammonium fluoride for Cd and ammonium nitrate for Pb, but they dried and ashed their sample externally prior to flameless atomic absorption analysis. Hinderberger eit al. (19) used NH4H2P04and a L'vov platform to eliminate matrix interference but their procedure involved a time-consuming digestion step prior to matrix modification. Hodges and Skelding (17)used phosphioric acid and ammonium molybdate for P b in urine; however, their procedure also involved digestion of the urine sample and addition of other reagents such as iodine and ascorbic acid. In spite of using a matrix modifier composed of ammonium nitrate, diammonium hydrogen phosphate, and 'Triton X-100, Bruhn and Navarrete (18)found it necessary to use the method of standard addition for determining Cd in urine. Because of the ultratrace levels of Cd (0-2 ng/mL) and P b (0-20 ng/mL) found in the urine of normal population, it is desirable to have a direct in situ methodl in order to minimize contamination problems. Also, the met hod chosen should be simple, rapid, and sensitive to facilitate large throughput, of samples. In this paper we describe a simple, rapid, and sensitive in situ diammonium hydrogen phosphate-nitric acid-electrothennal atonnizatiori atomic absorption spectrophotometric procedure for Cd in human urine; also reported are results of an ammonium nitrate-nitric acid-electrothermal atomization method for P b in urine sampleai.
EXPERIMENTAL SECTION Apparatus. A Perkin-Elmer Model 603 atomic absorption spectrophotometer equipped with a HGA-500 graphite furnace and a deuterium arc background corrector and Varian Techtron hollow cathode kunps were used for the determination of cadmium and lead. Reagents. Certified atomic absorption standards containing 1000 mg each of Cd(I1) and Pb(I1) per litler were obtained from Fisher Scientific. Fresh working standards of lower concentrations were prepared daily by serial dilution of the stock solutions in high-purity water. A 10% aqueous solution each of diammonium hydrogen phosphate and ammonium nitrate (Baker Analyzed Reagents, J. T. Baker Chemiical Co., Phillipsburg, NJ) was prepared. Each solution was purified by extraction with ammonium pyrrolidinedithiocarbamate and water-saturated methyl isobutyl ketone (25). The aqueous phase in each case was stored separately in a 1-L Nalgene linear polyethylene bottle. All other reagents and solutions used weire of the highest purity available. Also, prior to use all the glass and plastic labwares were cleaned as described in a previous publication (25). Sample Collection. Fresh urine samples were collected from voluntary laboratory plersonnel in 115-mL sterile, disposable polypropylene containers (Cat. no. (28841-201, Canadian Laboratory Supplies, Ottawa, Canada). The samples were usually analyzed immediately after sampling. If there was more than a 5-h delay between the collection of the sample and its analysis, the samples were refrigerated at 4 "C. Analytical Procedure. Cadmium. To 2.5 mL of urine contained in a 5-mL Pyrex-glass volumetric flask were added I00 pL of 10% (NH,),HPOh and 100 p L of 10% "OB. The volume was adjusted to 5 mL with high-purity water, the flask was stoppered, and the solution was then vigorously agitated for 20
1065
Table I. Optimized Instrumental Parameters for the Determination of Cd and Pb in Human Urinea setting
for Cd
for Pb
hollow cathode lamp current, mA wavelength, nm slit, nm nitrogen flow,b mL/min integration time, s drying temp, "C drying time (ramp/hold), s ashing temp, "C ashing time (ramp/hold), s atomization temp, "C atomization time (ramp/hold), s cleaning temp, "C cleaning time (ramp/hold), s
6.0 228.8
7.0 283.3
0.7
0.7
300 5.0 120 30120 500 10130 1500 1/3 2700 113
300 5.0 120 30/30 500 10/40 2300 1/3 2700 113
a Perkin-Elmer Model 603 atomic absorption spectrophotometer equipped with a deuterium arc background corrector and a Model HGA-500 graphite furnace. Temperatures given represent the digital display on the control panel of the HGA-500. The internal purge gas flow was operational only during the drying and ashing cycles; there was no gas flow during the atomization cycle.
s by using the Fisher Scientific Vortex-Genie. A 10-pL aliquot of this solution was injected into a pyrocoated graphite tube. The cadmium in the sample was vaporized,using the dry-char-atomize program of the HGA-500 developed in this study. The average absorbance values of the four to five injections were obtained and were corrected for the reagent blank. The amount of cadmium in the sample was calculated by reference to linear working curves prepared from fresh aqueous standards in 0.2% each of (NH4),HP04 and HNO,. Lead. The procedure for Pb was the same as above except for the following To 2.5 mL of the sample were added 250 pL of a 10% solution of NH4N03and 500 pL of 10% "OB. The Pb content of the urine sample was obtained by reference to a calibration plot constructed from a human Urine Control (Product no. 2934-80, Level I, Fisher Scientific) fortified with varying amounts of the element. The optimum amount of (NH4)HP04or NH4NOBused in the above procedures was obtained by doing the study at 0,0.05,0.10, 0.20,0.30,0.50, 1.0, 1.5, and 2.0% of phosphate or nitrate while keeping the nitric acid concentration constant (0.5% in the case of Cd and 1.0% in the case of Pb). The optimum concentration of nitric acid was arrived at by repeating the procedure at 0,0.05, 0.10,0.20,0.30,0.50,1.0,1.5, and 2.0% HNO, while maintaining the phosphate (0.2%) or nitrate (0.5%)concentration constant. To study the effect of urine-matrix on the absorption signal of Cd and Pb, two urine controls (Product no. 2934-80, Level I and Product no. 2935-80, Level 11, both obtained from Fisher Scientific) spiked with various amounts of Cd (0.5, 1.0, and 2.0 ng/mL) and Pb (10, 20, and 40 ng/mL) were used.
RESULTS AND DISCUSSION Table I shows the optimized instrumental parameters. In particular, the charring temperature must by optimized for maximum matrix loss and minimum analyte loss. As shown in Figure 1,use of simple diluents such as water, Triton X-100, or nitric acid did not seem effective because a t the optimum permissible ashing temperatures of 300-400 "C for Cd, the organic components of the urine matrix were not completely ashed resulting in smoke production during atomization and consequent attenuation of the source and background beams. On the other hand, use of temperatures a t which the organic matter could be completely ashed resulted in the volatile loss of the analyte. However, it can be seen from Figure 1 that the use of the (NH4)2HP04-HN03matrix modifier permitted an optimum ashing temperature of 600 "C. At this temperature the organic matter is completely ashed without the concurrent volatization of Cd. The use of the (NH4)2HP04-HN03matrix modifier for the determination of P b in urine was not successful because the
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ANALYTICAL CHEMISTRY, VOL. 55, NO. 7, JUNE 1983 0.15 1
Table 11. Precision at Various Concentrations of Cd and Pb in Human Urine cadmium, ng/mL std % coeff mean dev var
lead, ng/mL std % coeff mean dev var
0.49 0.93 1.20 2.42
Within-Run Precisiona 0.05 10.2 15.2 0.03 3.2 24.4 0.06 5.0 36.0 0.10 4.1 46.8
1.8 2.3 2.2 1.9
11.8
0.44 0.97 1.16 2.35
Day-to-Day PrecisionC 0.05 13.6 15.8 0.05 5.2 23.9 0.06 5.2 36.8 0.13 5.5 46.3
2.1 2.5 2.6 2.0
13.3 10.4 7.1 4.0
9.4 6.1 4.1
0 2 0 0 4 0 0 8 0 0 8 0 0 x ) o
ASHING TEMPERATURE ("C)
Flgure 1. Effect of charring temperature on the absorbance peak height for cadmium in a 2-fold diluted urine sample supplemented with 2 ng of Cd/mL: 0, water; 0 , 1% nitric acid; 0 ,0.5% ammonium nitrate; H, 0.5% Triton X-100, A, 0.2% diammonium hydrogen phosphate -t 0.2% nitric acid.
a Based on 20 repetitive measurements. The precision studies in the case of Pb were done with spiked urine samples. Based o n 90 determinations over a 30-day period.
atomic absorption signal of P b in the case of some urine samples was depressed by about 70% relative to its value in the aqueous (NH4),HP04-HN03 medium. No significant improvement was noticed by changing the concentrations of phosphate and nitric acid (up to 2% in each case). The signal could be restored to its value in the aqueous medium by a 20-fold dilution of the urine sample as opposed t o a 2-fold dilution used in the present work. However, the P b levels in the urine of unexposed individuals would not be detected a t such a high dilution. Figure 2 shows the optimum ashing temperatures attainable for P b in the Urine Control, Level 11, sample diluted 1:l with water, ",NO3, (NH4),HP04plus "OB, and ",NO3 plus "OB. Although the optimum ashing temperature in each case is sufficient to ensure maximum charring of the organic matter, the sensitivity of the atomic absoption signal is optimum in the case of NH4N03-HN03. Therefore, this composite matrix modifier was chosen for determining P b in urine. The use of nitric acid was necessary to ensure complete ashing of the organic matter and to minimize background absorption. Absorbance-peak height values obtained for Cd in five random urine samples were independent of the (NH4)2HP04 concentration in the 0.1% to 1.0% range and of the nitric acid
ASHING TEMPERATURE ("C)
Flgure 2. Effect of charring temperature on the absorbance peak height for lead in a 2-fold diluted Urine Control, Level 11, sample containing 54.5 ng of Pb/mL; 0, water 0 , 0.5% ammonium nitrate 4- 1% nitric acid: 0,0.2% diammonium hydrogen phosphate -t0.2% nitric acid; H, 0.5% ammonium nitrate.
concentration in the 0.05% to 2.0% region. In the case of Pb, no significant changes in the signal were observed from 0.5% to 1.5% NH4NOBand from 0.5% to 2.0% nitric acid. Because the most consistent results were obtained with 0.2% (NH4),HP04 plus 0.2% H N 0 3 for Cd and with 0.5% ",NO3 plus 1.0% H N 0 3 for Pb, these combinations were selected as the matrix modifier solutions of choice in the determination of Cd and Pb, respectively, in human urine samples. The calibration curve for cadmium in an aqueous 0.2% (NH,) *HP04plus 0.2% H N 0 3 medium, in the Urine Control, Level I, and in five randomly selected urine samples analyzed
Table 111. Analytical Recovery of Cadmium and Lead Added to Human Urine Cadmium concn in sample,'" ng/mL
0.4 ng/mL
0.6 ng/mL
0.8 ng/mL
1.0 ng/mL
0.49 0.60 0.93 1.09 2.74
108.9 i 3.5c 104.4 i 4.1 104.4 i 4.0 111.1i 5.1 97.8 + 3.6
106.0 4.2 110.5 ?: 2.8 106.0 z 5.2 107.5 + 5.5 101.5 I2.7
100.0 f 2.8
100.0
% recovery after the addition o f b
104.6 + 97.7 + 96.6 + 108.1 +
3.5 4.7 4.2 4.3
i
107.3 i 104.8 i 92.7 i 94.6 +
3.4 5.5 4.9 5.0 3.3
Lead % recovery after the addition of
10.0 ng/mL
20.0 ng/mL
40.0 ng/mL
112 + 4.OC 84.0 + 4.6 84.0 t 5.1 88.0 i 4.2 86.0 + 4.8 108.0 i 4.4
107.6 + 92.5 i 98.1 i 88.7 i 94.3 + 96.2 t
108.0
2.6 4.5 3.2 3.1
4.9 4.1
*
106.3 i 94.6 + 101.8 t 100.9 i 101.8 i
2.6 5.7 3.7 2.0 2.1 2.3
60.0b ng/mL 105.6 i 2.7 105.5 i 4.8 101.8 i 4.1 106.1 i 5.2 99.4 i: 3.3 98.8 + 3.9
a Concentration in the original urine sample. The samples were diluted 2-fold except for sample no. 5 (2.74 ng/mL) The data for the spikes refer to concentrations in the diluted sample, Measure of precision is which was &fold diluted,
the standard deviation at the 95% confidence interval.
All the samples analyzed contained Pb below the detection limit
of the proposed method ( < 4 . 1 ng/mL). The samples were diluted 2-fold prior to analysis.
ANALYTICAL CHEMISTRY, VOL. 55, NO. 7, JUNE 1983
Table IV. Comparison of Some Methods for Cadmium in Human Urine samPle no. 1 2 3 4 5 6 7 8 9 a
present method 1.16 i 1.09 0.36 i 0.93 i0.49 i 2.74 i 0.9'7 i 0.91 i 0.60 i
0.04c
* 0.06
0.02 0.03 0.05 0.06 0.08 0.04 0.02
APDCMIBKETA (1
0.88 i 0.04 0.97 i: 0.01 0.33 i 0.02 0.89 i 0.02 0.39 i 0.03 2.42 5 0.10 0.89 i 0.03 0.94 i 0.02 0.45 f 0.02
BruhnNavarrete 0.92 i 0.04 1.04 i 0.06 0.28 i 0.04 0.71 i 0.04 0.38 i 0.02 2.64 i 0.04 0.85 i 0.04 0.87 i 0.06 0.50 ?: 0.10
The procedure given for drinking water samples in ref
26 was applied to urine samples. Instead of water samples,
the same aliquot of urine samples were processed. From ref 18. Measure of precision is the standard deviation at the 95% confiidence interval. by the method of standard addition paralleled one another over the linear analytical region. Thus, the slopes (absorbance vs. mg L-l) for the standard curve, the urine control, and the standard addition plots were 114.3 (standard deviation 6.2), 111.5 (standard deviation 7.7), and 113.3 (standard deviation 6.9), respectively. The parallel nature of the three calibration plots and the nearly identical values of the three slopes clearly show the absence of interference from the major organic and inorganic concomitants in the urine samples. Since there were no significant differences among the three slopes, the concentration of Cd in the urine samples can be calculated by comparison to linear working curves prepared from aqueous standards containing 0.2% each of (NH4)2HP04and "OB. Neither the use of matrix-matched Calibration curves nor the use of the method of standard addition is necessary. The slopes (absorbance vs. mg L-l) for the standard curve in the NH4N013-HN03 medium, the Urine Control, Level I, and the standard addition curve in the case of P b are 4.26, 2.70, and 2.82, respectively. The significant difference in the value of the slope between the aqueous and urine calibration plots shows that the matrix effects are not completely eliminated by the use of the 0.5% N04N03-1% H N 0 3 solution. Use of up to 2% each of NH4N03and H N 0 3 resulted in no significant improvement. As a result thie concentration of P b in urine can be calculated only by reference to matrix-matched calibration curves prepared from Urine Control, Level I. The matrix-matched calibration curves can be used because no significant differences in the slopes were observed for calibration plots derived from at least five irandom urine samples and the Urine Control, Level I. The sensitivity (concentration for 0.0044 absorbance unit), detection limit (3 standard deviation of blank), and linear range for Cd in the 2-fold diluted urine sample are (ng/mL) injection. The 0.05,0.09, and 0.0-1.5, respectively, for a 1 0 - ~ L respective corresponding values for P b are (ng/mL) 1.6, 4.1, and 0.0-80.0. The detection limits are sufficiently low for base line studies and screening programs. Table I1 gives the within-run and day-to-day precision for Cd and P b in the urine samples. Considering the levels in-
'1067
volved, both the within-run and between-day precision are judged to be acceptable. Also, the good day-to-day precision data obtained over a 30-day period shows the stability of Cd and P b in the urine samples once they are diluted with the appropriate matrix-modifier solutions. In the absence of a standard urine reference material certified for Cd and Pb, only an indirect measure of accuracy could be obtained in terms of recovery studies and comparison studies. Table I11 shows that the mean analytical recovery for Cd and P b in some urine samples supplemented with various levels of these elements are satisfactory. In the comparison study the values obtained for Cd by the present method in nine random urine samples were compared with those obtained by an APDC-MIBK-GFAA procedure (26) and by the matrix-modification procedure of Bruhn and Navarrete (18). In the case of Pb, the proposed method was compared with an APDC-MIBK-GFAA method (26). The results for Cd show satisfactory agreement among the three methods (Table IV). All the samples analyzed contained P b at or below the detection limit, i.e., 4.1 ng/mL. Thus, the satisfactory analytical recoveries and the good agreement with other methods suggest that the (NH4)2HP04-HN03-ETA method for Cd and the NH4N03-HN03-ETA method for P b are reasonably accurate. Registry No. Pb, 7439-92-1; Cd, 7440-43-9.
LITERATURE CITED (1) Nomiyama, K. Sci. TotalEnviron. 1980, 14, 199-232. (2) Tsuchiya, K. "Handbook on the Toxicology of Metals"; Friberg L., et al., Eds.; Elsevler/North-Holland Biomedical Press: Amsterdam, 1979; pp 451-484. (3) Lauwerys, R. R.; Buchet, J. P.; Roels, H. Int. Arch. Occup. Environ. Health 1976, 3 6 , 275-285. (4) Elinder, C.-G.; Kjellstrom, T.; Linnman, L.: Pershagen, G. Environ. Res. 1978, 15,473-484. (5) Stoeppler, M. "Analysis of Cadmium in Biological Materials"; Proceedings of the Third International Conference; International Lead Zinc Research Organization: New York, 1981; pp 95-102. (6) Legotte, P. A,; Rosa, W. C.; Sutton, D. C. Talanta 1980, 27, 39-44. (7) Kubaslk, Irl. P.; Yolosln, M. T. Clin. Chem. (Winston-Salem, N.C.) 1973, 19, 954-5358, (8) Boiteau, H. L.; Metayer, C. Analusis 1978, 6 , 350-358. (9) Allah, P.; Mauras, Y. Clin. Chim. Acta 1979, 9 1 , 41-46. (10) Sperllng, K.-R.; Bahr, B. 2.Anal. Chem. 1980, 301, 29-32. (11) Smith, 8. M.; Grlfflths, M. 8 . Analyst (London) 1982, 107,253-259. (12) Stoeppler, M.; Brandt, K. Z . Anal. Chem. 1980, 300, 372-380. (13) Lund, W.; Larsen, B. V.; Gundersen, N. Anal. Chim. Acta 1978, 81, 3 19-324. (14) Ross, R. 1.; Gonzalez, J. G. Anal. Chim. Acta 1974, 70, 443-447. (15) Carmack, G. D.; Evenson, M. A. Anal. Chem. 1979, 51, 907-911. (16) Lagesson, V.; Andrasko, L. Clin. Chem. (Winston-Salem, N.C.) 1979, 25, 1948-1953. (17) Hodges, D. J.; Skeldlng, D. Analyst (London) 1981, 106, 299-304. (18) Bruhn, C. F:.; Navarrete, G. A. Anal. Chim. Acta 1981, 130, 209-214. (19) Hinderberger, E. J.; Kaiser, M. L.; Kolrtyohann, S. R. Atom. Spectrosc. 1981, 2, 1-7. (20) Shimlzu, T.; Shijo, Y.; Sasakl, K. BunsekiKagaku 1981, 3 0 , 770-774. (21) Gardiner, P. E.; Ottaway, J. M.; Fell, G. S. Talanta 1979, 26, 841-847. (22) Vesterberg, 0.; Wrangskogh, K. Clin. Chem. (Winston-Salem, N.C.) 1978, 24, 681-685. (23) Pleban, P. A.; Pearson, K. H. Clin. Chim. Acta 1979, 9 9 , 267-277. (24) Pleban, P. A,; Pearson, K. H. Anal. Lett. 1979, 12 (B), 935-950. (25) Subramanian, K. S.;MBranger, J. C. Clin. Chem. (Wlnston-Salem, N . C . ) 1981, 27, 1866-1871. (26) Subramanlan, K. S.; MBranger, J. C. In?. J. Environ. Anal. Chem. 1979, 7 , 25-40,
RECENEDfor review November 23,1982. Accepted February 1, 1983.
