M332 and MK617: two new potential pyrite reference materials for in situ sulfur isotope analysis

Abstract

With the growing use of in situ techniques such as Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS), Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS), and NanoSIMS in sulfur isotope studies, new sulfide reference materials (RMs) are needed to meet increasing analytical demands and ensure accuracy. This study introduces two new natural pyrite RMs, M332 and MK617, characterized for in situ sulfur isotope analysis using LA-MC-ICP-MS, LG-SIMS, and NanoSIMS. Their sulfur isotope homogeneity was rigorously confirmed by in situ analysis, which agree with isotope Ratio Mass Spectrometry (IRMS) bulk analyses within analytical uncertainty, validating their reliability as RMs. The recommended δ³⁴S values, determined by IRMS, are 24.96 ± 0.22‰ (2 SD, n = 10) for M332 and −4.43 ± 0.21‰ (2 SD, n = 12) for MK617. Additional SIMS analyses yielded δ³³S values of 12.89 ± 0.60‰ (2SD, n = 104) for M332 and −2.23 ± 0.35‰ (2SD, n = 120) for MK617, further supporting their isotopic consistency. In conclusion, M332 and MK617 exhibit good isotopic homogeneity and span a wide surfur isotope range, making them highly suitable reference materials for calibrating in situ sulfur isotope studies across diverse geochemical and biological process applications.