Comparison of wet digestion procedures for the determination of cadmium and lead in marine biological tissues by Zeeman graphite furnace atomic absorption spectrophotometry.

Three wet digestion procedures, namely, nitric acid/sulphuric acid, nitric acid/hydrogen peroxide and nitric acid/perchloric acid were compared for their relative efficiency in determining cadmium and lead in marine biological tissues. The nitric acid/perchloric acid procedure was the most efficient, whereas the nitric acid/hydrogen peroxide procedure was the least efficient. The nitric acid/sulphuric acid procedure was also found to be effective but there was a problem with the method as the presence of sulphuric acid in the matrix markedly suppressed the absorbance signals especially for lead analysis and thus reduced sensitivity. The addition of ascorbic acid as matrix modifier improved sensitivity. However, this analysis still required the standard addition method. No apparent interferences were encountered for cadmium analysis.