Determination of cadmium in sediment by isotope dilution inductively coupled plasma mass spectrometry using a co-precipitation separation technique

A co-precipitation separation method is described for the determination of cadmium in sediment by isotope dilution inductively coupled plasma mass spe ctrometry. A sediment sample is digested with HNO3, HClO4 and HF, and then ammonia solution is added. Zirconium and Sn, which are sources of spectral interference on Cd isotopes in ICP-MS measurements, are co-precipitated wit h hydrolysis compounds of Al and Fe (major constituents in the digested sol ution). However, cadmium is masked with ammonia and still remains in the su pernatant. The efficiency of the removal of Zr and Sn in the co-precipitati on separation are both around 99.5%, and the recovery of Cd is > 80%. The m easured n(Cd-111)/n(Cd-112) ratios in the unspiked digested solution of sed iment reference materials (PACS-1 and NIES No. 2) after the co-precipitatio n and separation are in good agreement with those for a standard Cd solutio n, and the procedural blank of the co-precipitation separation is extremely low (below the detection limit of ICP-MS). The analytical results obtained for Cd in PACS-1 and NIES No. 2 were 2.396 +/- 0.033 mug g(-1) (value +/- expanded uncertainty) and 0.819 +/- 0.011 mug g(-1), respectively, which ar e in good agreement with the certified values (PACS-1: 2.38 +/- 0.20 mug g( -1), and NIES No. 2: 0.82 +/- 0.06 mug g(-1)). This pretreatment method is simple and reliable for the determination of Cd in sediments by ID-ICP-MS.