Determination of Mg isotope ratios without column chromatography for carbonates using sulphuric acid and MC-ICP-MS

This study presents a practical method for high-precision Mg isotope determination without column chromatography for carbonate samples using sulphuric acid and MC-ICP-MS. The protocol uses the chemical reaction between carbonate and sulphuric acid to generate CaSO4 precipitation and MgSO4 supernatant, which is used to determine Mg isotopic ratios. The matrix effects and the sulphuric acid conditions were rigorously examined using Nu Plasma II with a wet plasma mode. The precision and accuracy of this method were tested by measurements of the carbonite standard material JDo-1 over four months. The δ26Mg of JDo-1 is -2.32 ± 0.11 ‰ (2SD, n = 34) relative to DSM3, well consistent with the recommended value (-2.35 ± 0.15 ‰). The robustness of this method was further assessed by replicated analyses of ten Chinese carbonate reference materials that covered a large range of MgO contents from 5.98 wt.% to 20.91 wt.%.