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Anal. Chem. 1985, 57. 2478-2481
Table VI. V Concentrations, bg/g
material
determn
oyster tissue citrus leaves bovine liver human serum
6 6
5 7
concn 2.316 0.245 0.0987 0.00263
RSD, % 0.28 2.0 1.6 11.6
by the ratio measurement. The relative magnitude and uncertainty of the blank correction are listed in columns 4 and 5, and the relative uncertainty of the spike concentration is listed in column 6. The calculated standard error which combines the sources of uncertainty (21) is listed in column 7 of Table V ( N = 4 for ratio measurement; N = 3-5 for blank measurement; N = 4 for spike calibration). Vanadium Content. The V contents of the materials analyzed here are summarized in Table VI. The measurement uncertainty, as expressed by the standard deviation of the six or seven samples analyzed, includes the above-mentioned uncertainties for a single measurement and any uncertainty caused by sample inhomogeneity. The reproducibility of the mass spectrometric measurement procedure was not explicitly checked by replicate determinations of V in subsamples from a single dissolved sample. However, the measured uncertainty for replicate determinations from different bottles of each SRM can be compared with the uncertainties associated with single measurements for each SRM (column 7, Table V). It is possible that the significantly larger measurement uncertainty for the replicate determinations of V in citrus leaves and human serum is caused by the variability of V in these materials. Nonetheless, such inhomogeneity is minor at the ultralow V levels of these materials, which can now be used for the validation of V ultratrace measurement in biological matrices. Registry No. V, 7440-62-2.
LITERATURE CITED (1) Underwood, E. J. “Trace Elements in Human and Animal Nutrition“; Academic Press: New York, 1977; pp 388-397.
(2) Cornelis, R.; Versieck, J.; Mees, L.; Hoste, J., Barbier, F. 8iol. Trace Elem. Res. 1981, 3 , 257-263. (3) Nielson, F. H. I n “Inorganic Chemistry in Biology and Medicine”; Martell, A. E., Ed.; American Chemical Society: Washington, DC, 1980; pp 32-35. (4) Ward, N.; Bryce-Smlth, D.; Minskl, M.; Zaaljman, J.; Pim, B. I n “Trace Element-AnalyticalChemistry in Medicine and Biology, Vol. 2”; Blatter, P., Schramel, P., Eds.; Waiter de Gruyter: New York, 1983; pp 483-498. (5) Haas, W. J.; Fassel, V. A.; Grabau, F.; Kniseley, R. N.; Sutherland, W. L. I n “Ultratrace Metal Analysis in Biological Sciences and Environment”; Amerlcan Chemical Society: Washington, DC, 1979; p 93. (6) Mianzhi, 2.; Barnes, R. M. Appl. Spectrosc. 1984, 38, 635. (7) Flesch, G. D.; Capellen, J.; Svec, H. J. Adv. Mass Spectrom. 1966, 3 , 571. (8) Balsiger, H.; Mendia, M. D.; Peily, 1. 2 . ; Llpschutz, M. E. Earth Planet. Scl. Lett. 1976, 28, 379-384. (9) Peily, I.2.; Llpschutz, M. E.; Balsiger, H. Geochim. Cosmochim, Acta 1970, 34, 1033-1036. (10) Kuehner, E. C.; Alvarez, R.; Pauisen, P. J.; Murphy, T. J. Anal. Chem. 1972, 4 4 , 2050-2056. (11) Kingston, H. M.; Barnes, I.L.; Brady, T. V.; Rains, T. C.; Champ, M. A. Anal. Chem. 1978, 50, 2064. (12) Moody, J. R. Phiios. Trans. R . SOC.London, A 1962, 305, 669-680. (13) Peiser, H. S.;Holden, N. E.; De Bievre, P.; Barnes, I. L.; Hagemann, R.; DeLaeter, J. R.; Murphy, T. J.; Roth, E.; Shima, M.; Thode, H. G. Pure Appl. Chem. 1984, 56, 695. (14) Riley, J. P.; Taylor, D. Anal. Chim. Acta 1968, 4 1 , 175-178. (15) Shields, W. R., Ed. ”Analytical Mass Spectrometry Section: Summary of Activities;” National Bureau of Standards: washington, DC, 1967; NBS Tech. Note (U.S.) 426. (16) Fritz, J. S.; Abbink, J. E. Anal. Chem. 1982, 3 4 , 1080. (17) Moore, L. J.; Machlan, L. A.; Shields, W. R.; Garner, E. L. Anal. Chem. 1974, 46, 1082. (18) Chen, J.; Wasserburg, G. J. Anal. Chem. 1981, 53, 2060-2067. (19) Jamleson, R. T.; Schreiner, G. D. L. I n “Electromagnetically Enriched Isotopes and Mass Spectrometry”; Smith, M. L.; Ed.; Butterworths Sclentiflc Pubiicatlons: London, 1956; pp 169-176. (20) Murphy, T. J. I n “Accuracy in Trace Analysis: Sampling, Sample Handling, and Analysis”; Natlonal Bureau of Standards: Washington, DC, 1976; NBS Spec. Publ. 422, pp 509-539. (21) Eisenhart, C. Science 1969, 160, 1201-1204.
RECEIVED for review May 20, 1985. Accepted July 1, 1985. Certain commercial equipment, instruments, or materials are identified in this paper to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
Graphite Furnace Atomic Absorption Spectrometry with Nitric Acid Deproteinization for Determination of Manganese in Human Plasma Kunnath S . Subramanian* and Jean-Charles Meranger Environmental Health Directorate, Health and Welfare Canada, Tunney’s Pasture, Ottawa, Ontario K I A OLZ, Canada A nltrlc acid deprotelnlzatlon-graphlte furnace atomlc absorptlon spectrophotometric method has been developed for determlnlng nanogram per mllllllter levels of manganese In human plasma samples. Values for manganese In the sample are obtained by the use of matrlxmatched callbratlon graphs. The detection llmft (three standard devlatlons of blank) for manganese Is 0.1 ng/mL, and Is sufficiently low for base llne studies. Data are presented on the degree of accuracy and preclslon of the method. At least 15 samples can be analyzed per hour. The sensitlvlty and slmpllclty of the procedure make It attractlve for routine environmental surveillance Involvlng large throughput of samples.
The biological role of manganese has not yet been com-
pletely elucidated because of the difficulty of measuring this metal in biological materials (1). Manganese occurs at the sub-nanogram-per-milliliterlevels in human plasma or serum (2) necessitating the use of very sensitive analytical methods. Among the various techniques used for measuring manganese in plasma/serum, electrothermal atomization atomic absorption spectrometry (ETAAS) is gaining increasing attention because of its excellent sensitivity and selectivity for this metal. Several ETAAS methods have been published for manganese in plasma/serum (3-6). Sample treatments vary widely and include none (7-11), dilution with water (3, 12, 13), Triton X-100 (4, 14), and ethylene glycol (5), and matrix-modification with ammonium oxalate (6). In our hands all these methods resulted in the deposition of a carbonaceous crust in the graphite tube partially obstructing the light path
0003-2700/85/0357-2478$01.50/0 0 1985 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985
and leading subsequently to imprecise results. Nitric acid has been shown to effectively deproteinize the blood and serum matrix and thus prevent the buildup of organic residue in the graphite tube of the heated graphite atomizer in the determination of A1 (15),Cd (16),Ni (In,and Pb (18). In this paper we explore the feasibility of using nitric acid to deproteinize the plasma samples prior to analyzing them for manganese by graphite furnace atomic absorption spectrometry (GFAAS). The results of this study are reported here.
EXPERIMENTAL SECTION Apparatus. A Perkin-Elmer Model 603 atomic absorption spectrophotometer equipped with an HGA-500 graphite furnace, a deuterium-arc background corrector, an AS-1 autosampler incorporating a 10-pL pump, a PRS-10 printer, and a Perkin-Elmer hollow cathode lamp operated at 12 mA and a resonance wavelength of 279.9 nm (spectral band-pass, 0.7 nm) was used for the determination of manganese. Nitrogen was used as the purge gas. Reagents. High-purity water was obtained by passing tap water through a cellulose adsorbent and two mixed-bed ion-exchange columns, and finally distilling in a Corning AG-11 unit. The quality of the water conformed to ASTM Type 1specification (19). In addition, the manganese level in the water was below the GFAAS detection limit (3 times the standard deviation of the blank) of 0.1 ng/mL. A certified atomic absorption standard containing 1000 mg of manganese per liter was obtained from Fisher Scientific. Fresh working standards of lower concentrations were prepared daily by serial dilution of the stock solution with high-purity water. A 50% solution of nitric acid was prepared by diluting 50 mL of concentrated HN03 (Baker Ultrex) to 100 mL with high-purity water. The diluted acid was stored in a precleaned Nalgene linear polyethylene bottle with tight-fitting polyethylene screw caps. All other reagents and solutions used were of the highest purity available. Sampling of Plasma. Human whole blood samples (about 10 mL) were drawn by venepucture through 22 gauge, 2.5 cm polyethylene cannulas ("IV-Cath", catalog no. 6745, BectronDickinson Co., Rutherford, NJ) into trace-element-free, sodium heparinized vacutainers (catalog no. 6527, Becton-Dickinson Co., Rutherford, NJ) according to the procedure of Sunderman et al. (17). Basically, the procedure involved cleansing the antecubital fossa of the arm with ethanol and allowing it to dry by evaporation. A tourniquet was then applied, the cannula was inserted into an antecubital vein, the stylus of the cannula was removed, the cannula was flushed with at least 5 mL of blood, the blood was discarded, and a further 10 mL of blood was taken into a polypropylene Monovette syringe (catalog no. HR1-8888-100107, Sherwood Medical Industries, Inc., St. Louis, MO). Each whole blood sample was immediately centrifuged at 9OOg for 15 min. The supernatant plasma (about 4 mL) was transferred into 5-mL polystyrene test tubes with tight-fitting polyethylene caps and stored at 4 "C until the time of analysis. Analytical Procedure. To 250 pL of plasma contained in a polycarbonate centrifuge tube was added 50 pL of 50% Ultrex grade nitric acid. The volume was adjusted to 500 pL with high-purity water. The centrifuge tube was stoppered with a polyethylene cap and the sample was vigorously agitated for 30 s with a Fisher ScientificVortex-Genie followed by centrifugation at 2575g for 3 min. The protein-free supernatant was transferred into the polyethylene sample cups of the autosampler. The cups containing the reagent blanks (5.0% HNO,), samples, and plasma-based calibration standards (prepared by using bovine plasma supplemented with manganese to final concentration values of 0.2,0.5, 1.0, 2.0, and 4.0 ng/mL and taken through the same analytical procedure as the samples) were arranged in the sample tray of the autosampler. A plasma-based manganese standard supplemented with 1.0 ng/mL Mn (in addition to the endogenous Mn level of the plasma) was placed in the sample tray once every four samples to act as a check for drift in Calibration during the run. The autosampler was switched on and a 10-pL aliquot was transferred into the pyrocoated graphite tube of the HGA-500 furnace atomizer. The HGA-500heating program was initiated. The manganese in the sample was atomized by
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raising the temperature to 120 "C in 20 s and holding at that temperature for 30 s (drying), raising the temperature from 120 "C to 200 "C in 30 s and holding at 200 "C for 20 s (drying),heating to 1100 "C in 10 s and holding there for 20 s (ashing), heating to 2500 "C in 1 s and holding for 5 s (atomization), and finally heating to 2600 OC in 1 s and holding for 2 s (cleaning). The nitrogen flow was set at 300 mL/min throughout the temperature program, excepting at atomization time during which the flow was interrupted. The reagent blanks, samples, and standards were measured in duplicate. If the duplicates differed in peak-height absorbance by more than lo%, the analysis was repeated. Four replicate injections were made for each aliquot, thus making a total of eight measurements. The peak absorbance values of these eight measurements were averaged and corrected for the reagent blank. The manganese concentration of the sample was obtained by reference to the plasma-based calibration plots. The optimum amount of nitric acid used in the above procedure was obtained by doing the study at 0.2,0.5, 1.0, 2.0, 3.0,4.0,5.0, 7.0, and 10.0% of the acid. Contamination Control. All labware (including the test tubes, centrifuge tubes, and autosampler cups) was cleaned by a sequential tap water rinse, 24-h soak in 5% Ultrex nitric acid, and thorough rinsing (at least 6 times) in high-purity water. After the cleaning operation, any ware found to contain detectable levels of manganese was rejected. The manganese content of the trace-element-free vacutainers was below the GFAA detection limit. The entire analytical operation was performed in a class-100 laminar-flow clean hood.
RESULTS AND DISCUSSION The specified instrumental conditions for the determination of manganese in human plasma were obtained by a systematic evaluation of the temperature program of the graphite furnace atomizer, optimal spectrometer adjustments, and sample volume. A two-step drying program and a 10-pL aliquot of the plasma were chosen to minimize uneven drying and spattering of the samples. The use of an ashing temperature of 1100 " C and deproteinization of the plasma sample with nitric acid ensured complete ashing of the organic matter and the absence of any carbonaceous residue buildup inside the graphite tube. The formation of this carbonaceous crust was a persistent problem when the plasma sample was injected directly into the graphite tube (7-11). The problem could not be eliminated even with the use of diluents such as water (3, 12,13),Triton X-100 (4,14),and ethylene glycol (5) or with the use of ammonium oxalate (6) as a matrix modifier. The presence of this residue causes random attenuation of the analyte and background beams leading subsequently to erratic results. In the case of the Triton X-100 procedure ( 4 ) , the residue buildup begins to seriously impair the results only after the sixth sample injection. Therefore it is possible to obtain acceptable results with the Triton X-100 method ( 4 ) if one removes the residue from the tube after every six injections. The residue can be removed with a cotton swab followed by heating the tube to a temperature of 2700 "C for 3 s. The optimum amount of nitric acid required to completely deproteinize the plasma samples and to prevent the buildup of the "carbon mount" in the graphite tube was found to be 2 3 % (final acid concentration in the sample). The peak absorbance values obtained for manganese in the plasma sample were independent of the nitric acid concentration in the 3-10% range. However, the supernatant after centrifugation appeared clear only at nitric acid concentration 2 5 % . Therefore a 5% acid concentration was maintained in the sample solution. Higher acid concentrations were not used because of their corrosive effect on the atomizer and oxidative attack on the graphite tube. Concentrations below 3% caused buildup of residue due to incomplete deproteinization; also the supernatant after centrifugation appeared turbid. The peak absorbance signal of manganese increased with increasing atomization temperature but an atomization temperature of 2500 "C was chosen; above 2500 O C the background
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 13, NOVEMBER 1985
Table I. Precision at Various Concentrations of Manganese in Human Plasma
mean concn of Mn, ng/mL 0.63 0.90 1.13 1.50 2.09
within-run precisiona std % coeff dev of var
day-to-day precisionb std % coeff dev of var
0.09 0.08 0.05 0.07 0.07
0.11 0.09 0.07 0.07 0.08
14.3 8.9 4.4 4.7 3.4
17.5 10.0 6.2 4.7 3.8
Based on 20 repetitive measurements. *Based on 80 measurements over a 20-day period.
Table 11. Analytical Recovery of Manganese Added to Human Plasma concn in sample: ng/mL
% recovery after the addition ofb 0.5 ng/mL 1.0 ng/mL 2.0 ng/mL
0.70 1.04 1.29 1.65
110.3 f 2.9' 107.7 f 3.0 109.5 f 3.4 108.8 f 3.2
105.2 f 1.7 104.1 f 2.3 102.9 f 2.7 103.0 f 2.5
96.6 f 0.2 100.2 i 1.9 98.9 f 2.1 102.1 f 1.7
Concentration in the original sample. The samples were diluted 2-fold. *The data for the spikes refer to concentrations in the diluted sample. Measure of precision is standard deviation.
noise signal increased considerably (0.003 absorbance units at 2500 "C vs. 0.014 absorbance units at 2600 "C and 0.019 absorbance units at 2700 "C) most likely due to incandescent emission from the graphite tube passing through the monochromator. The instrument apparently could not correct for this dc emission signal. The background noise signal had to be kept to a minimum owing to the sub-nanogram-per-milliliter values of manganese in the plasma of normal individuals. The dilution factor had to be kept to a minimum (Le., 2-fold) because of the ultralow levels of manganese present in human plasma samples. However, at the 2-fold dilution there was evidence of nonspecific background signal from the plasma matrix. Background compensation was therefore found to be essential for reliable manganese results. In this work a deuterium arc background corrector was used to compensate for the nonatomic contribution to the analyte signal. The use of nitric acid and a 2-fold dilution of the plasma sample ensured that the compensating capabilities of the deuterium arc were not exceeded. The background ab~~~
sorbance for a 2-fold-diluted plasma sample containing 5% nitric acid was between 0.05 and 0.06 absorbance unit which was well within the compensating abilities of the deuterium arc background corrector. The manufacturer (20)recommended the use of a spectral band-pass of 0.2 nm for Mn. However, a t this bandwidth the deuterium arc intensity was so low that the hollow cathode lamp current had to be reduced to 4 mA from the recommended value of 30 mA in order to match the background intensity. Under these conditions the peak absorbance values were not very precise. Therefore, the bandwidth was increased to 0.7 nm; this provided increased deuterium arc intensity such that the hollow cathode lamp current could be increased to 12 mA to obtain a matching source-beam intensity. Although at 0.7 mm, the absorbing manganese triplet at 279.5, 279.8, and 280.1 nm was included, no spurious signals were introduced. In addition, the signals obtained were more precise. The slopes (absorbance vs. nanograms per milliliter) for manganese in aqueous 5% nitric acid, in a pooled bovine plasma sample, and in five randomly selected human plasma samples were 0.024, 0.028, and 0.029, respectively. The significant differences in the value of the slope between the aqueous and plasma calibration plots showed that the matrix effects from the major inorganic salts, especially sodium chloride, present in the plasma sample were not completely eliminated by the use of nitric acid. In fact, use of up to 10% nitric acid resulted in no significant improvement. Therefore, aqueous calibration plots could not be used for calculating the concentration of manganese in the plasma samples. On the contrary, no significant differences were observed in the slopes derived from the calibration graphs of bovine plasma and the five human plasma samples. Therefore, concentration of manganese in the sample could be calculated by reference to the bovine-serum-based calibration plot. There is no need to use the method of standard additions. The sensitivity (concentration for 0.0044 absorbance unit), detection limit (3 times standard deviation of the blank), and linear range for manganese in the 2-fold-diluted plasma sample were (ng/mL) 0.16, 0.10, and 0-4, respectively, for a 10-pL injection. No improvement in sensitivity or detection limit was noticed using the L'vov platform. Nevertheless, the detection limit is sufficiently low for base line studies and screening programs. Table I gives the within-run and day-to-day precision for manganese in some plasma samples. Considering the levels involved, both the within-run and between-day precision are gratifying. Also, the good day-to-day precision data over a 20-day period show the stability of manganese in the plasma
~
Table 111. Comparison of Some Methods for Manganese in Human Plasma" sample no.
present method
Triton X-100
sample no.
present method
Triton-X-100
GFAA'
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1.52 i O.OOb 0.88 f 0.08 0.73 f 0.07 0.70 f 0.06 1.48 f 0.09 1.57 f 0.17 1.29 f 0.07 0.93 f 0.10 0.78 f 0.09 1.22 f 0.09 2.09 f 0.07 0.73 f 0.05 1.39 f 0.06 1.12 f 0.08 0.63 f 0.09
1.37 f 0.11 1.15 f 0.10 0.68 f 0.08 0.77 f 0.09 1.58 f 0.11 1.58 f 0.14 1.58 f 0.21 1.16 f 0.15 1.10 f 0.12 1.26 f 0.11 2.00 f 0.20 0.91 f 0.09 1.26 f 0.13 1.37 f 0.12 0.68 f 0.08
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
1.50 f 0.07 1.13 f 0.00 1.04 f 0.09 1.00 f 0.05 0.93 f 0.08 1.39 f 0.09 1.65 f 0.11 0.67 f 0.06 0.70 f 0.07 1.13 f 0.05 0.90 f 0.08 1.48 f 0.09 1.04 f 0.09 0.67 f 0.07 1.07 f 0.07
2.00 f 0.11 1.68 f 0.09 1.58 f 0.22 1.47 f 0.13 1.47 f 0.14 1.37 f 0.11 1.26 & 0.10 0.82 & 0.10 0.64 f 0.08 1.14 f 0.11 0.77 f 0.09 1.26 f 0.11 1.37 f 0.12 0.73 f 0.10 1.47 f 0.21
GFAA
Values are in ng/mL. *The measure of precision in the standard deviation. The correlation coefficient based on simple linear regression equation is 0.83. 'From ref 4.
Anal. Chem. 1985, 57, 2481-2486
samples once they are deproteinized with the 5% nitric acid solution. In the absence of a standard plasma reference material certified for manganese, only an indirect measure of accuracy could be obtained in terms of recovery studies and comparison studies. Table I1 shows that the mean analytical recovery for manganese in some plasma samples supplemented with various levels of this element are satisfactory. In the comparison study, the values obtained for manganese in the present study in 30 plasma samples were compared with those obtained by a Triton X-100-GFAA procedure ( 4 ) . The results in Table I11 show satisfactory agreement between the two methods. Thus, the satisfactory analytical recoveries and the good agreement with the Triton X-100 method suggest that the nitric acid deproteinization-GFAA method for manganese is reasonably accurate. The values in Table I11 range from 0.63 to 2.09 ng of Mn/mL of plasma and were obtained from the samples of psychiatric patients who were on neuroleptic drugs and who were suffering from tardive diskinesia. The plasma/serum manganese values for normal individuals range from 0.54 to 34.3 ng/mL although recent data suggest a value between 0.36 and 1.04 ng/mL (21). If the value of 0.36 to 1.04 ng/mL is accepted as "normal", the values obtained for the psychiatric patients in this work are elevated. It would be interesting to enquire whether such an elevation is caused by an iatrogenic effect.
ACKNOWLEDGMENT The authors are grateful to J. Thakar of the Royal Ottawa Hospital for the provision of the plasma samples used in this
2481
study and to John Connor for technical assistance.
Registry No. Mn, 7439-96-5. LITERATURE CITED (1) Underwood, E. J. "Trace Elements in Human and Animal Nutrition", 4th ed ; Academic Press: New York, 1977. (2) Versieck, J.: Cornelis, R. Anal. Chlm. Acta 1980, 116, 217-254. (3) Halls, D. J.; Fell, G. S. Anal. Chlm. Acta 1981, 129, 205-211. (4) Brodie, K. B.; Routh, M. W. Clin. Biochem. 1984, 17, 19-26. (5) Favier, A.; Ruffieux, D.; Alcaraz, A.; Maljournal, B. Clin. Chim. Acta 1982, 124, 239-244. (6) Wei, F. S.;Qu, W. 0.; Yin, F. Anal. Left. 1982, 158, 721-729. (7) Grafflage, B.; Buttgereit, G.; Kubler, W.; Mertens, H. M. 2.Klin. Chem. Kin. Biochem. 1974, 12, 287-283. (8) Bek, J.; Janougkovi, J.; Moldan, B. At. Absorpt. News/. 1974, 13, 47-48. (9) Alt, F.; Massman, H. Z . Anal. Chem. 1976, 2 7 9 , 100-101. (IO) D'Amico, D. J.; Klawans, H. L. Anal. Chem. 1976, 4 8 , 1469-1472. ( 1 1 ) Hoffmann, H. Klin. Wochenschr. 1980, 56, 157-158. (12) Ross, R. T.; Gonzalez, J. G. Bull. Environ. Contam. Toxicol. 1974, 12, 470-474. (13) Muzzarelii, R. A. A.; Rocchettl, R. Talanta 1975, 22, 683-685. (14) Pleban, P. A.; Pearson, K. H. Clin. Chem. (Winston-Salem, N . C . ) 1970, 2 5 , 1915-1918. Brown, S.; Bertholf, R. L.; Wills, M. R.; Savory, J. Clin. Chem. (Winston-Salem, N . C . ) 1984, 3 0 , 1216-1218. Stoeppler, M.; Brandt, K. 2.Anal. Chem. 1980, 300, 372-380. Sunderman, F. W., Jr.; Crisostomo, M. C.; Reid, M. C.; Hopfer, S. M.; Nomoto, S. Ann. Clin. Lab. Sci. 1984, 14, 232-241. Stoeppler, M.; Brandt, K.; Rains, T. C. Analyst (London) 1978, 103, 714-722. (19) "AnnuacBook of ASTM Standards"; A.S.T.M.: Philadelphia, PA, 1981; Part 31: D1193-77: DO 29-31. (20) "Analytical Methods?& Atomic Absorption Spectrophotometry"; The Perkin-Elmer Corp.: Norwalk, CT, January 1982. (21) Versieck, J. Trace H e m . Med. 1984, 1 , 2-12.
RECEIVED for review May 2, 1985. Accepted July 11, 1985.
Determination of Arsenic and Selenium in Fat Materials and Petroleum Products by Oxygen Bomb Combustion and Automated Atomic Absorption Spectrometry with Hydride Generation Hisatake Narasaki Department of Chemistry, Faculty of Science, Saitama Uniuersity, Shimo-Okubo, Urawa 338, Japan
Arsenic and selenlum In butter and polythenes were determined, after combustlon In the oxygen bomb, by automated atomlc absorption spectrometry wlth hydride generatlon. Recoveries were checked wlth inorganic or organlc arsenic and selenium added to samples. When the gas in the bomb was released Into a glass trap after combustion and ,the washings were acid-digested lncludlng a combustion capsule, the recoverles were quantltatlve. The detection llmlts were 5 and 10 ppb for arsenic and selenlum, respectlvely. The results obtained by the method were in good agreement wlth the certlfled values of blologlcal standard reference materlals. Automated devices were used at some stages In the sample preparatlon.
Pretreatment of organic materials is a troublesome problem when fat materials and petroleum products are decomposed
for the determination of volatile elements without loss. The decomposition of fatty materials with the recycling digestion apparatus was not perfect and small amounts of fat remained in the digest ( I , 2). Bajo et al. (3) obtained quantitative recoveries of As, Hg, Se, etc. added to organic materials using HzS04+ HNO, at atmospheric pressure, but 100% HN03 was required to destroy the pure fat materials. Perchloric acid is not recommended to oxidize fat, since it is highly reactive and immiscible with the reagent (4). Pressure-resistant closed vessels appear to be most desirable to determine these elements. An explosion was reported when fat was decomposed with H2S04 + "OB in the Parr Teflon bomb (5). The oxygen bomb was used for the determination of arsenic (6, 7) and of selenium (8-10), but the methods of the determination used were of no chemical reliance. The Analytical Methods Committee (11) checked the recovery of selenium by atomic absorption spectrometry (AAS) with hydride generation after the de-
0003-2700/85/0357-2481$01 .50/0 0 1985 American Chemical Society
