Effective Correction of Mass Bias for Rhenium Measurements by MC‐ICP‐MS

Abstract

The geochemistry of Re‐Os and the recent use of Re as a non‐traditional stable isotope both need accurate and precise quantification of 187Re/185Re ratios. This paper reports rhenium isotopic data obtained from the analysis of a standard solution and geological samples by MC‐ICP‐MS. We show that measured isotopic ratios are modified by matrix effects that cannot be accounted for by the standard solution bracketing technique. The bias resulting from measurements on a spiked (185Re‐enriched) sample is shown to alter the apparent Re concentration by several percent. When spiking samples and calibrators with tungsten, simultaneous measurement of tungsten and rhenium isotopes compensates for the matrix‐induced modification of mass bias. Rhenium and tungsten are shown to have different fractionation factors. This may be due to the fact that the two elements fractionate in a different but systematic way, or that the reference isotopic ratios used for elemental Re and W are incoherent with one another. The consistency of fractionation through time can be used to obtain an empirical relationship between W and Re measured ratios from a standard solution to obtain a sample's fractionation‐corrected 187Re/185Re spiked ratio on samples containing pg g−1 levels of Re, even if some matrix capable of affecting mass bias remains in the final solution.