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and molybdenum in sediments may in fact be slightly optimistic in that they do not take into account the very large background shifts below about 210 nm encountered with samples containing high aluminum concentrations (1 7). The detection limits for elements such as arsenic and molybdenum with lines in this region are almost certain to be poorer in the presence of a high concentration of aluminum than in the 1 M HC1 solutions used for calibration in this work. An increase in the background a t the As I 193.696 nm line can also result from the broadened wing of the C I 193.091 nm line. Carbon may be present as an impurity in the argon or as residual soluble organic materials in the samples. The slightly less intense As I line at 197.197 nm would perhaps be less susceptible to carbon interference, but the sensitivity of both of these lines is inadequate for accurate arsenic determination in these samples.It appears that the sensitivity of ICP-AES is nearly sufficient for accurate cadmium determinations in marine sediments. The estimated detection limit for the Cd I 228.802 nm line used in this work is 0.2 pg/g. This line was chosen because of its high sensitivity and its freedom from iron interferences. This latter attribute is not shared by alternative cadmium lines of comparable sensitivity at 214.438 nm and 226.502 nm. However, the 228.802 nm line is subject to possible arsenic interference because of the As 1228.812 nm line. Although the interference is not so severe in our highresolution instrument that it could not 228.812 nm handled by a correction factor, this approach would require an accurate arsenic determination, which for these sediments was precluded by inadequate sensitivity. Perhaps the best line for cadmium determination in marine sediments would be the ion line a t 226.502 nm. Although this line is overlapped by an iron line a t 226.505 nm, the correction factor is relatively small (2.3 X and here a t least the concentration of the interferent can be very accurately determined. This approach was applied successfully to determine cadmium at about the 2 pg/g level in a fresh water sediment but was unsuccessful for a marine sediment in which the cadmium concentration was about 0.2 pg/g (18). This is hardly surprising when it is noted that multiplication of the correction factor by a typical solution iron concentration of 300 mg L-l yields a bogus cadmium concentration of 0.07 mg L-l, equivalent to about 7 pg/g of cadmium in the sediment! Thus, it appears that accurate determinations of Cd in marine sediments by ICP-AES will usually require a preconcentration of the Cd or at least a separation from the matrix. LITERATURE CITED14) Botto, R. I. In "Developments In Atomlc Plasma Spectrochemical Analysis"; Barnes, R. M., Ed.; Heyden and Son: Philadelphia, PA, In 433-437. 679-680. 21 68-21 73. 147-152. press. (15) Larson, 0. F.; Fassel. V. A.; Winge, R. K.; Kniseley, R. N. Appl. Spectrosc. 1978, 30, 384-391. (16) Fassel, V. A.; Katzenberger, J. M.; Winge, R. K.Speclation and quantitative analysis of arsenl...

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