Determination of the Isotopic Composition of Osmium Using MC-ICPMS

摘要

Despite its widespread applications in geology, all osmium isotope ratio measurements are either uncalibrated or rely to on the veracity of the uncalibrated 1937 Nier values by adopting c o them as normalizing constants typically in conjunction with an exponential mass bias correction model. In this study, isotope ratios . of osmium were determined in six commercial osmium materials, including the DROsS standard and a new NRC isotopic osmium E reference material OSIS-1, by MC-ICPMS. We use a previously optimized and validated regression mass bias correction model to correct instrumental isotope fractionation effects which does not rely either on Nier's values or on a strictly mass-dependent behavior of the isotopes. Deviations from mass-dependent fractionation (mass independent fractionation) were observed for osmium isotopes in MC-ICPMS with the most dramatic effect occurring for Os-187, wherein, on average, close to half-percent bias in the isotope ratio Os-187/Os-188 was observed as a result of imposing Russell's law.