A Novel Method for the Dissolution of Cassiterite and Accurate Tin Isotope Measurement

Tin isotopes have become a valuable tracer for geological, archaeological and cosmochemical investigations because of their distinctive multi‐isotopic system of ten stable isotopes and their affinity for both sulfide and chalcophile phases. However, the refractory nature of cassiterite (SnO 2 ) presents a major challenge for Sn isotope measurement, as its resistance to conventional acid digestion leads to prolonged, incomplete dissolution and problematic isotopic fractionation. Thus, this study presents a novel method for cassiterite dissolution employing the sealed Carius tube technique, with an evaluation of three acid systems: 11.6 mol l ‐1 concentrated HCl, 7.6 mol l ‐1 HBr, and 9.1 mol l ‐1 HBr. A key finding is that complete removal of residual HBr via pre‐treatment is critical to avoid analytical interference. Applying this approach, the mean δ 122/118 Sn 3161A for sample DL 16 was ‐0.04 ± 0.02‰ (2 s , n = 16). A 9.1 mol l ‐1 HBr solution demonstrated the highest dissolution efficiency, achieving complete cassiterite breakdown about 700% faster than previous methods. δ 122/118 Sn 3161A was consistent across the different acid systems and varying recovery rates, confirming minimal isotopic fractionation. Method validation using the cassiterite reference material #CAS 2 yielded δ 122/118 Sn 3161A = 0.29 ± 0.06‰ (2 s , n = 4), in agreement with the certified reference value. The proposed method offers several advantages: (1) high recovery rates within short processing times; (2) complete dissolution of cassiterite; (3) negligible Sn isotopic fractionation. This protocol effectively overcomes key limitations of conventional approaches, such as incomplete dissolution, use of hazardous reagents, and potential isotopic bias, thereby establishing a reliable procedure for precise Sn isotope measurement in geochemical and planetary research.