Three new potential sulfur reference materials (pyrite, gypsum, and arsenopyrite) for in situ sulfur isotope analysis by laser ablation MC-ICP-MS

Sulfur isotopes serve as critical tracers for understanding the material sources and cycling in earth science. The in situ sulfur isotope ratio analysis by laser ablation multiple-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) has been a proven important technique, yet the precision and accuracy of measurement are limited by matrix-matched reference materials. In this study, we investigated three new potential reference materials (pyrite NWU-Py, gypsum NWU-Gy and arsenopyrite NWU-Apy) for sulfur isotope ratio analysis by LA-MC-ICP-MS. The ultra-fine powders of pyrite, gypsum and arsenopyrite were synthesized into a solid block using the fast-hot-pressing sintering method (FHP). The reliability of these reference materials was evaluated by large quantities of sulfur isotope measurements by LA-MC-ICP-MS, with mean δ³⁴S values of 3.48 ± 0.26‰ (2SD, n = 787) for NWU-Py, 18.19 ± 0.32‰ (2SD, n = 290) for NWU-Gy, and −0.19 ± 0.32‰ (2SD, n = 383) for NWU-Apy, which are highly consistent with those obtained from isotope ratio mass spectrometry (IRMS). Furthermore, the F-testing and H-index indicate that the three materials have excellent homogeneity of sulfur isotope compositions. Therefore, NWU-Py, NWU-Gy, and NWU-Apy can serve as bracketing matrix-matched reference materials for in situ sulfur isotope measurement by LA-MC-ICP-MS.