A novel chemical purification method for accurate Sn isotope measurement by MC-ICP-MS

The geological and environmental applications of tin (Sn) isotopes have been hindered by the shortcomings of chemical purification, as severe loss of Sn would occur during sample preparation (evaporation and re-dissolution) and column separation, triggering isotope measurement bias. In this study, we develop a novel and robust separation method to purify Sn from natural samples for accurate isotope measurements. The protocol is established by combining two chromatographic columns loaded with AG 1-X8 and AG 50W-X12 resins, and optimizing the sample evaporation and re-dissolution procedures. The method is proven to efficiently eliminate the main interferents such as Ag, Zn, Mo, Cd and Sb and results in low procedural blank (0.54 +/- 0.21 ng, n = 3), quantitative recovery (95-102%, n = 32) and good external precision (delta 120Sn of 0.02-0.04 parts per thousand, in 55 measurements) for isotope measurement. The protocol is further applied to seven geological and environmental reference materials (BCR-2, BHVO-2, AGV-2, JG-2, AC-E, PACs-2 and GSS 7) and new values are reported for both odd (delta 119Sn and delta 117Sn) and even (delta 120Sn and delta 122Sn) Sn isotope ratios. This study demonstrates clearly the potential application of our method for studying the geochemical behaviors of Sn and its isotopes in various aspects. A novel two-step chromatographic separation procedure is developed for the Sn isotope chemical purification. With this method, both even and odd Sn isotope ratios can be precisely determined without double-spike correction.