Analysis of cadmium and lead in sediment by isotope-dilution ICP-MS

An isotope-dilution mass-spectrometric method was applied to the determination of Cd and Pb in sediment. The co-precipitate separation method using hydroxides of Al and Fe as a carrier precipitant was examined to overcome the spectral interference of ZrO+ and Sn+ on Cd isotopes. The amount of 204Hg that interferes with the 204Pb measurement was estimated from a measurement of 202Hg. The measured 111Cd/112Cd of digested solutions of pond-sediment reference material (NIES No.2) and a CCQM sample after co-precipitation were almost identical to that in a Cd standard solution. The interference of 204Hg on 204Pb was satisfactorily corrected by a mathematical correction method. The analytical results for Cd and Pb in NIES No.2 are 0.819 ± 0.011 μg g-1 (value ± expanded uncertainty) and 103.81 ± 0.76 μg g-1, respectively, and were in good agreement with their certified values (Cd: 0.82 ± 0.06 μg g-1, Pb: 105 ± 6 μg g-1). The present method was also applied to a CCQM key comparison (CCQM-K13, Cd and Pb in sediment); good analytical results for both Cd and Pb were obtained. (author)