In-situ osmium isotope ratio analyses of iridosmines by laser ablation-multiple collector-inductively coupled plasma mass spectrometry
TanakaLaboratory for Planetary Sciences, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo, 152, JapanDepartment of Earth and Planetary Sciences, Nagoya University, Chikusa-ku 1-1, Nagoya, 464-01, JapanIn-situ isotopic ratio analyses of Os for iridosmine samples have been made by a laser ablation–multiple collector–inductively coupled plasma mass spectrometer (LA–MC–ICPMS). A frequency-quadrupled Nd-YAG UV laser (266 nm) which produces pit sizes of 10–15 μm was used to ablate iridosmine samples. The technique developed in this study enabled us to measure small deviations in isotopic and elemental ratios of solid geochemical samples with an analytical uncertainty smaller than 0.05%. The analytical precision of Os isotopic ratio measurements achieved by the present LA–MC–ICPMS technique was comparable to those achieved by negative thermal ionisation mass spectrometry (NTIMS). We have determined Os isotopic ratios for three iridosmine placers from the Urals, California and Hokkaido, Japan. The resulting 187Os/188Os ratio for iridosmines from the Urals (0.124786±0.000030, 2σ) exhibits an excellent agreement with the value reported by è