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

Abstract

Antimony (Sb) isotopes are robust and useful geochemical markers for tracing the sources, transport and transformation of Sb in various environments. Accurate Sb isotope analysis necessitates rigorous offline chemical separation and/or preconcentration, generally 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). However, the applicability of these techniques across diverse sample matrices has not been well explored. In this study, we performed the first systematic comparison and evaluation of these three separation protocols under the same criteria and further optimized them 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 the same geological sample sets further validated the accuracy of the three optimized protocols, while their applicability was shown to be matrix-dependent. This work highlights the importance of performing a critical comparison of various analytical methods and establishes practical guidelines for the accurate measurement of Sb isotope ratios using different separation protocols with MC-ICP-MS.