Accurate analysis of selenium in water and serum using ETV-ICP-MS with isotope dilution

A procedure for the determination of selenium in water and serum using elec trothermal vaporisation isotope dilution inductively coupled plasma mass sp ectrometry (ETV-ID-ICP-MS) is described. The Se-82: Se-77 isotope ratio was measured throughout, following spiking of the samples with a solution cont aining the enriched Se-77 isotope. Elimination of interferences was achieve d with an optimised ETV temperature program. Parameters such as peak measur ement mode, dwell time, points per spectral peak and number of replicates w ere evaluated to establish optimum conditions. The accuracy and precision o f the method are demonstrated with the analysis of several certified refere nce materials namely TMRAIN-95 (spiked rainwater), TMDA-54.2 (spiked soft w ater), LGC 6010 (hard drinking water) and NIST 1598 (bovine serum). Results for all reference materials were within the certified limits. Isotope dilu tion analysis of TMRAIN-95, TMDA-54.2, LGC 6010 and NIST 1598 gave % RSD va lues (n = 3) of 0.80, 0.07, 0.48 and 0.06%, respectively, compared with 5.5 0, 2.79, 1.15 and 0.92% obtained with the conventional ETV-ICP-MS procedure , thus illustrating improvements in precision with the ETV-ID-ICP-MS method . The uncertainties for the two methods were calculated following ISO guide lines. The uncertainty for the IDMS procedure was 3.4 times smaller than th at for the conventional ETV-ICP-MS method (2.26% and 7.73%, respectively).