One‐Column Pre‐Separation of Si, Fe, Mg and Ca from Reference Materials for Isotope Measurements

Silicon, iron, magnesium and calcium isotopes are widely used in geochemical and cosmochemical studies. However, these isotopes often require separate purification procedures, resulting in high sample consumption and potential isotope decoupling caused by sample heterogeneity. Here, we develop a one‐column pre‐separation method for the simultaneous purification of Si, Fe, Mg and Ca isotopes from a single sample aliquot. Samples were digested by alkali fusion to prevent Si loss, followed by cation‐exchange chromatography to complete separation of Si, Fe, Mg and Ca. Silicon, Fe and Mg isotopic measurements were made by multi‐collector inductively coupled plasma‐mass spectrometry (MC‐ICP‐MS), whereas Ca isotopes were measured by thermal ionisation mass spectrometry (TIMS). The method was validated using a series of geological reference materials spanning ultramafic to felsic rocks, including dunite (DTS‐2), basalt (BCR‐2, BHVO‐2 and JB‐2), andesite (AGV‐2 and JA‐2), granite (GSP‐2) and rhyolite (RGM‐2), as well as two meteorites (Allende and Murchison). All measured isotope ratios of these four elements are consistent with previously reported values within uncertainties. This efficient simultaneous separation and analysis method minimises sample consumption and avoids isotope decoupling associated with heterogeneous materials. This approach is therefore particularly suitable for precious and compositionally heterogeneous extra‐terrestrial samples.