A novel sample decomposition technique at atmospheric pressure for the determination of Os abundances in iron meteorites using isotope dilution inductively coupled plasma-mass spectrometry

Abstract

A safe and reliable analytical technique for the determination of Os abundances in ten iron meteorites of various chemical groups was developed using isotope dilution inductively coupled plasma-mass spectrometry coupled with a sample decomposition technique. A major advantage of the sample decomposition technique developed here is that the pressure inside the reaction flask is not increased through the decomposition reaction because the flask is a fully opened system, obviating the risk of explosion of the glass apparatus. Another advantage is that there is no restriction in the sample size being decomposed. In this study, about 2 g of metallic sample were decomposed safely, and this sample size, >10 times larger than that typically used for the Carius tube technique, allows one to obtain more reliable Os data for heterogeneous samples. The metallic samples were decomposed in a glass flask purged with Ar. Since the O₂ was purged from the reaction flask, Os was not oxidised to volatile OsO₄, thereby preventing significant evaporation loss of Os. The typical recovery of Os throughout the sample decomposition and separation processes was >80%, and the total Os blank through the decomposition of a 1 g amount of sample was less than 20 pg. Os abundances were determined by means of stable isotope dilution mass spectrometry using a ¹⁹⁰Os-enriched isotopic tracer. Except for Sikhote–Alin, the measured Os abundances in almost all the iron meteorites exhibited a good agreement with the previously published Os abundance data, within the analytical uncertainty achieved in this study (2–5%). For the Sikhote–Alin meteorite, on the basis of a better correlation between Os and Ir abundances, we believe that our Os abundance data should be more reliable. The Os abundance data obtained in this work clearly demonstrated the suitability of the newly developed sample decomposition procedure for low level Os determinations.