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Figure 7. The maximum bismuth concentration, 0.053 ng/L, was found in the surface water. If the ratio between dissolved and particulate bismuth is the same as that of coastal waters, the total bismuth concentration in the surface water would be about 0.15 ng/L, and this is at least 2 orders of magnitude lower than the previously reported values. The high bismuth in the surface water may originate from either aeolian inputs or from fluvial sources. The second bismuth maximum occurred at the oxygen minimum depth, which might result from Bi regeneration from organic matter. Rapid decrease of bismuth at subsurface and below 2 km depth are in accord with the high geochemical reactivity of bismuth. Verticle profiles of manganese in ocean waters reported recently (11,12) are very similar to those of bismuth. Implications of the similarity between manganese and bismuth are not clear as yet. The more pronounced bismuth decrease in deep waters suggests a higher rate of bismuth scavenging.
ACKNOWLEDGMENT The author expresses his sincere thanks to E. D. Goldberg, K. K. Bertine, and M. Koide for advice, guidance, and manuscript review. K. W. Bruland of Center for Marine Studies,
University of California at Santa Cruz, and J. Martin of Moss Landing Marine Laboratories obtained the Pacific Ocean waters, for which the author is most grateful.
LITERATURE CITED (1) Gillaln, G.; Duyckaerts, G.; Dlsteche, A. Anal. Chim. Acta 1979, 706, 23-37. (2) Gilbert, T. R.; Hume, D. N. Anal. Chim. Acta 1973, 65, 451-459. (3) Portman, J. E.; Riley, J. P. Anal. Chim. Acta 1966. 34, 201-210. (4) Andreae, M. 0.Anal. Chem. 1977, 49, 820-823. (5) Hodge, V. F.; Seldel, S. L.; Goldberg, E. D. Anal. Chem. 1979, 5 7 , 1256-1 259. (6) Andreae, M. 0.;Froellch, P. N., Jr. Anal. Chem. 1981, 53, 287-291. (7) Fernandez, F. J. At. Absorpt. News/. 1973, 12 (4), 93-97. (8) Flanagan, F. J. Geocbim. Cosmocbim. Acta 1973, 3 7 , 1189-1200. (9) Smith, A. E. Analysf (London) 1975, 100, 300-306. (10) Fleming, H. D.; Ide, R. G. Anal. Chim. Acta 1976, 83, 67-82. (11) Martin, J. H.; Knauer, G. A. Earth Planet. Scl. Lett. 1980, 5 1 , 266-274. (12) Landing, W. M.; Bruland, K. W. Earth Planet. Sci. Lett. 1980, 49, 45-56. (13) Goldberg, E. D.; Gamble, E.; Griffin, J. J.; Koide, M. Estaurine Coastal Mar. Sci. 1977, 5 , 549-561.
RECEIVED for review February 3,1982. Accepted June 1,1982. This work was supported by the Office of Naval Research, Contract USN NO00 18-75-(2-0152.
Reduction of Interferences with Thiourea in the Determination of Cadmium by Electrothermal Atomic Absorption Spectrometry Masaml Suzukl" and Kiyohlsa Ohta Department of Chemistry, Faculty of Engineering, Mie University, Kamihama-cho, Tsu, Mie-ken 5 14, Japan
The determlnation of cadmium by electrothermal atomlc absorption spectrometry with a metal microtube atomizer uslng mlcrocomputer processlng was Investigated. Thlourea served to modify the interferences from concomltants during the atomlzatlon. No background correction was necessary for matrices In the proposed method. This method was applled to the determlnatlon of cadmium In blological samples. Sampies were digested wlth nitric acid In a pressure decomposltion vessel. No Interferences from concomitants were shown for determlnatlon of cadmium In blologlcal samples provlded thlourea was added. The method provides a slmpie and sufflcientiy sensitlve technique for cadmium determination.
Cadmium has received considerable attention because of its toxicological importance. Many workers have applied electrothermal atomic absorption with a graphite furnace or carbon rod atomizer for the determination of cadmium in biological samples ( I , 2). However, a correction is necessary for background absorption resulting from matrices. The background correction technique does not give an accurate result if cadmium reacts with matrices or their decomposition products. The method combined with electrodeposition or solvent extraction has also been reported for measurement of cadmium without interferences (3). In this paper, a method is presented which has been developed by use of microcomputer-processed atomic absorption
spectrometry with a metal microtube atomizer for the determination of cadmium in biological samples. This method allows highly sensitive work with small sample size. The effect of thiourea is demonstrated for modification of interferences from matrices.
EXPERIMENTAL SECTION Instrumentation. The monochromator, photomultiplier, and amplifier for atomic absorption measurements were the same as used previously ( 4 ) . The output signal from the amplifier was fed to a microcomputer (4,5).The signals were also monitored on a Memoriscope (Iwatsu MS5021). The molybdenum microtube atomizer (20 mm long and 2 mm bore) and absorption chamber (300mL) have been described ( 4 ) . The argon used as purge gas in the absorption chamber was mixed with hydrogen. Two light apertures (1 and 5 mm diameters, respectively) were positioned in front of the monochromator entrance slit so that the light beam from the hollow cathode lamp passed through the microtube and through the apertures. A cadmium hollow cathode lamp (Hamamatsu TV Co.) was used for atomic absorption measurement at 228.8 nm. The tube temperature was measured as described previously (4). The signal from the photodiode was fed to the microcomputer and recorded simultaneously with the absorption signal. All sample solutions were injected into the microtube by use of l-fiL glass micropipet. A Uni-seal decomposition vessel was used for digestion of samples. Reagents. Stock solution of cadmium nitrate (1mg Cd/mL) was prepared by dissolving pure metal in nitric acid and diluting with demineralized water. Chloride solution (1 mg/mL) was
0003-2700/82/0354-1686$01.25/00 1982 American Chemical Society
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Flgure 1. CRT display for effect of hydrogen flow rate on atomic absorption of cadmlum: (a) and (f) 500 mL/miru of Ar, (b) and (9) 20 mL/min of H2 and 480 mL/rnin of Ar, (c)and (h) 50 mL/mln of H2 and 450 mL/min of Ar, (d) and (i) 200 mL/min of H,? and 300 mL/min of Ar, (e)and (j) 500 mL/min of H,, (k) tempemparature increase; (A) 5 pg of Cd, (B) 5 pg of Cd
