Comparison and optimization of chromatographic separation methods for accurate measurement of antimony isotopic composition

Abstract

Antimony (Sb) isotopes are robust and useful geochemical parameter for tracing sources of Sb and its transport and transformation in various environments. Accurate Sb isotope analysis necessitates rigorous offline chemical separation and/or preconcentration, primarily achieved through three primary column-based techniques (with AG 1-X4/AG 50W-X8 resin, AG 50W-X8/thiol silica resin, and AG 50W-X8/Amberlite IRA 743 resin, respectively). However, their applicability and limitations across diverse sample matrices remain inadequately constrained. In this study, we performed for the first time a systematic comparison and evaluation of the three separation protocols under the same criteria, and made further optimization to address their respective matrix-specific limitations. Our optimized protocols yielded quantitative Sb recoveries (95–105%), and the measured δ123Sb values of geological reference materials by MC-ICP-MS agreed well with literature values within analytical uncertainty, demonstrating good inter-method reproducibility. Comparative δ123Sb determinations of same geological sample sets validated further the accuracy of three optimized protocols, though their applicability was shown to be matrix-dependent. This work highlights the importance of critical comparison of various analytical methods, and establishes practical guidelines for the accurate measurement of Sb isotope ratios using different separation protocols on MC-ICP-MS.