Simultaneous chemical separation of Ge and Sb from Sb-rich sulfide samples for isotopic analysis using MC-ICP-MS

Abstract

Germanium (Ge) and antimony (Sb) are critical metals that can be enriched in sphalerite of Pb-Zn deposits due to their chalcophile properties. The combined Ge-Sb isotopic systematics of these deposits serve as an essential tool for tracing metal sources and enrichment processes. However, the similar chemical behaviors of Ge and Sb hinder their simultaneous separation using existing purification protocols, and high Sb/Ge ratios in samples can affect the precise measurement of Ge isotope ratios. In this study, the adsorption behaviors of Ge and Sb on different resins were systematically investigated, and a sequential separation method combining solvent extraction and column chromatography was established. The method was validated using the Sb-rich sphalerite standard reference material GBW07270 with a Sb/Ge ratio of 42. Recoveries of Ge and Sb reached 97.4 ± 1.7% (2SD, n=5) and 99.3 ± 1.3% (2SD, n=5), respectively, with procedural blanks of 0.9 ng for Ge and 1.1 ng for Sb. Long-term reproducibility was assessed through repeated analyses of NIST SRM 3120a and NIST SRM 3102a, which yielded δ⁷⁴Ge and δ¹²³Sb values of 0.00 ± 0.09‰ (2SD, n = 239) and 0.00 ± 0.04‰ (2SD, n = 115), respectively. Isotope ratios obtained for the standard reference materials agreed well with published values, and no measurable Ge or Sb isotope fractionation was introduced by the separation procedure. Moreover, we report the Sb isotope ratios of GBW07270 for the first time. The accuracy of the method was further confirmed by standard addition experiments, in which all the linear regressions yielded R² > 0.98. The proposed simultaneous separation method for Ge and Sb provides a robust foundation for advancing stable isotope geochemistry of these critical metals.