The determination of arsenic and selenium in standard reference materials using sector field ICP-MS in high resolution mode

Sector field ICP-MS was used to analyse As and Se in a range of standard reference materials (NIST 1643d Water, NIST 1573a Tomato Leaves, NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine Level 2). A spectral resolution of m/Delta m = 7500 enabled As-75 and Se-77 to be separated from problematic ArCl interferences. Following microwave acid digestion, solid samples were typically diluted 1 + 99 prior to analysis, while the urine sample was diluted 1 + 9. The water sample was analysed undiluted and diluted 1 + 9. Despite near baseline spectral separation, As-75 and Se-77 were still found to be influenced by ArCl at high Cl concentrations, the effect being most pronounced for Se-77. When necessary Se-82 was also monitored to determine the accuracy of the Se-77 results. Detection limits (LOD, based on 3 sigma of 10 replicates) for As-75, Se-77 and Se-82 in ultra-pure water, 1% (w/w) HNO3 and 1% (w/w) HCl were similar to 0.1, similar to 0.2 and similar to 0.5 ng g(-1), respectively. Although signal intensities when using high resolution were similar to 1% of that found when using low resolution mode (m/Delta m = 300), measured As concentrations and certified values were found to agree to within +/- 11% for all samples analysed. The concentration of Se in NIST 1566a Oyster Tissue, NIST 2704 Buffalo River Sediment and Bio-Rad Reference Urine were found to be in agreement with certified values to within +/- 15-20%, as measured by Se-77. However, closer agreement (+/- 5%) was found when these samples were analysed using Se-82. The Se concentration in NIST 1643d Water was found to agree to within +/- 5% of the certified value (depending on dilution factor). Due to the low concentration of Se in NIST 1573a Tomato Leaves, quantitation was not possible (below LOQ, 10 sigma). As a consequence of the lower ion transmission when using resolution 7500, analytical precisions were found to be elevated over that normally observed using low resolution mode, typically +/- 5-20% (depending on analyte concentration and isotopic abundance).