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 electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (ETV-ID-ICP-MS) is described. The super(82)Se: super(77)Se isotope ratio was measured throughout, following spiking of the samples with a solution containing the enriched super(77)Se isotope. Elimination of interferences was achieved with an optimized ETV temperature program. Parameters such as peak measurement mode, dwell time, points per spectral peak and number of replicates were evaluated to establish optimum conditions. The accuracy and precision of the method are demonstrated with the analysis of several certified reference materials namely TMRAIN-95 (spiked rainwater), TMDA-54.2 (spiked soft water), LGC 6010 (hard drinking water) and NIST 1598 (bovine serum). Results for all reference materials were within the certified limits. Isotope dilution analysis of TMRAIN-95, TMDA-54.2, LGC 6010 and NIST 1598 gave % RSD values (n = 3) of 0.80, 0.07, 0.48 and 0.06%, respectively, compared with 5.50, 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 guidelines. The uncertainty for the IDMS procedure was 3.4 times smaller than that for the conventional ETV-ICP-MS method (2.26% and 7.73%, respectively).