Comparison of two gallium purification procedures for isotopic measurements by MC-ICP-MS in a set of silicate reference materials

Abstract

Gallium is a moderately volatile, moderately siderophile element with two stable isotopes: 69Ga and 71Ga. A general interest in Ga isotopes arose over the last few years, as its moderately volatile behavior potentially marks it as a useful tracer of various processes such as condensation and evaporation. Nevertheless, there is a lack of agreement between laboratories for consistent δ71Ga values in geological reference materials. In this work, we have developed and evaluated two methods for purification protocols leading to precise analysis of gallium (Ga) isotopic composition in silicate rock materials. The first method is a three-step column chemistry using the resins AG1-X8, HDEHP, and AG50W-X12 whereas the second method uses only two columns, AG1-X8 and AG50W-X8. The two methods were applied to a range of both synthetic (multi-element) solutions and geological samples. Both methods show comparable results with no isotope fractionation occurring during purification chemistry, allowing us to define the δ71Ga of selected USGS reference materials (BHVO-2, BCR-2, RGM-2). Similar to previously reported results, we also observe no Ga fractionation between distinct igneous terrestrial materials.