Evaluation of Simultaneous Analyte Leaching/Vapour Phase Introduction for Direct Osmium Isotope Ratio Measurements in Solid Samples by Double-Focusing Sector Field ICP-MS

The analytical performance of a method for Os isotope ratio measurement by double‐focusing, sector field ICP‐MS (ICP‐SFMS) was evaluated. The method is based on several optimised, concurrent processes: Os extraction from samples in hot concentrated nitric acid; separation of Os from the digest solution by the formation of volatile osmium tetroxide accelerated by continuous hydrogen peroxide addition; transport of analyte vapour by an oxygen flow into the ICP; and isotopic determination by ICP‐SFMS. Due to the very efficient utilisation of analyte (approaching 0.5‰), Os isotope ratio measurement could be performed at low pg levels. Combined with an ability to process sample sizes up to 2 g (up to 50 g if the organic matrix of biological or botanical samples is eliminated by ashing), materials with Os concentrations in the low, or even sub pg g^?1 range could be determined by this method. Given that two complete digestion/distillation systems were available for interchangeable use, throughputs of up to fifteen samples per 8 hour shift could be achieved. The method precision, evaluated as the long‐term reproducibility of ¹⁸⁷ Os/¹⁸⁸Os ratio measurements in a commercial Os reference sample containing 0.5 ng Os, was 0.16% relative standard deviation (RSD, 1s). The method has been applied to perform replicate ¹⁸⁷ Os/¹⁸⁸ Os ratio measurements on a suite of fifty reference materials of various origins and matrix compositions, with Os concentrations varying from < 0.1 pg g^?1 to > 100 ng g^?1, yielding an average precision of 3% RSD. Though none of the materials tested are certified for Os content or Os isotope composition, comparison of the obtained data with published Os isotope information for similar sample types revealed close agreement between the two. The method can also be used for the simultaneous, semi‐quantitative determination of Os concentrations.