A single-column and efficient procedure for separating Fe and Mg from geological materials for isotopic analyses using MC-ICP-MS

Abstract

Fe and Mg isotopes have increasingly served as combined proxies for geological processes. Fe and Mg isotope determination requires consuming different splits of samples and multi-column chromatographic purification to obtain pure Mg and Fe fractions in conventional chemical procedures, which is time-consuming and not suitable for rare and valuable samples. This study presents a novel and efficient chromatographic procedure to purify both Fe and Mg from geological matrices, using a single column loaded with AGMP-50 resin, followed by precise measurements of Fe and Mg isotopes by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). In our experiment, the Fe fraction was first collected using 7 mL of a mixture of 0.2 M HCl and 0.5 M HF, and then the Mg fraction was collected using 9 mL of 1.3 M HCl. This procedure is suitable for processing different types of rock samples and enabling an Fe recovery of >98% and full recovery of Mg, with effective removal of matrix elements such as Al, Ti, Na, K, Ca, and other trace elements. Using this method, the Fe and Mg isotopic compositions of various geological reference materials were reported. All of the Fe and Mg isotopic analytical results were in agreement with the reported data within analytical uncertainties, verifying that the method established here is robust and reproducible. Thus, this procedure will serve as a great option for obtaining both Fe and Mg isotopic compositions of geological samples and tracing geochemical or astrochemical processes in the future.