New potential reference materials for in-situ microscale Ag isotope analysis by fsLA-MC-ICP-MS

Silver isotopes are emerging geochemical tracers with increasing applications across earth sciences, environmental sciences, and archaeometry. Conventional Ag isotope analyses relying on chemical digestion of samples lack spatial resolution and are destructive, restricting their use for samples with micro-scale isotopic heterogeneity or precious archaeological artifacts. Laser ablation (LA)-MC-ICP-MS provides a minimally destructive alternative with high spatial resolution, but its analytical accuracy depends critically on suitable matrix-matched reference materials. Natural minerals with homogeneous Ag isotopic compositions are ideal candidate reference materials, yet they are scarce. To overcome this limitation, we developed synthetic gold- and silver-matrix materials as viable alternative calibrants for in-situ Ag isotope analysis. In addition, this study establishes a suite of natural reference materials, including native gold (Au1, Au2, and Au3), native silver (NAg), proustite (Pro1, Pro2, and Pro3), and argentite (Arg). In-situ Ag isotopic analyses demonstrate that all proposed candidate materials are isotopically homogeneous, with long-term analytical precision better than 0.08‰ (two standard deviations, 2SD). Both synthetic and natural reference materials serve as effective calibrants for LA-MC-ICP-MS, yielding Ag isotopic ratios consistent with solution-based values, indicating negligible matrix effects. These candidate reference materials are suitable as bracketing standards and quality control references for laser ablation Ag isotope analysis.