Synthetic CassiteriteReference Material for High-PrecisionIn Situ Sn Isotope Analysis by LA-MC-ICP-MS

Abstract Tin (Sn) isotopes in cassiterite (Cas) are important tracers of fluid evolution and Sn sources, but high-precision μm-scale in situ Sn isotope analysis remains constrained by the limited availability of suitable reference materials (RMs). Here, we report the development of a synthetic Cas-matrix RM to serve as a bracketing standard for laser ablation coupled with multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analysis. Ultrafine cassiterite powder was compressed, sealed in silver tubes, and sintered at 600 °C and 1.0 GPa, producing homogeneous pellets with yields up to 7 g per batch. Two independent laboratories, Northwest University (Xi’an, China) and Leibniz University Hannover (Germany), evaluated the isotopic uniformity (δ124/120Sn) of the pellets using femtosecond laser ablation (fs-LA)-MC-ICP-MS, yielding consistent δ124/120Sn values within analytical uncertainty. Solution nebulization (SN)-MC-ICP-MS analysis of the starting powder and pellet subsamples yielded a recommended δ124/120SnNIST SRM 3161a value of 0.63‰, with an expanded uncertainty (URM) of ∼ 0.07‰ (k = 2) and a precision of ±0.02‰ (2SD, n = 14). The agreement between in situ and solution measurements of natural cassiterite further validates the RM. A total of 28 g of synthetic cassiterite RM was prepared in four batches for distribution to the global geochemical community. This RM will advance Sn isotope analysis in cassiterite by providing a reliable standard for precise in situ measurements and interlaboratory comparison.