Sulfur-induced offsets in MC-ICP-MS silicon-isotope measurements

Abstract

Sample preparation methods for MC-ICP-MS silicon-isotope measurements often involve a cation-exchange purification step. A previous study has argued that this would suffice for geological materials, as the occasional enrichment of anionic species would not compromise silicon-isotope analysis. Here we report significant offsets in MC-ICP-MS silicon-isotope measurements induced by the presence of sulfur. We show that offsets in δ³⁰Si become significant above SO₄/Si ratios (wt.) of 0.02, reaching up to ca. +1.4‰ at SO₄/Si ratios above ∼0.2. This finding is particularly relevant for studies of sulfur-rich waters and silicified rocks where alteration was accompanied by sulfur-enrichments. We propose an additional purification step to remove sulfur from solid sample material.