Development of sulfide reference materials for in situ platinum group elements and S–Pb isotope analyses by LA-(MC)-ICP-MS

Abstract

The platinum group elements and sulfur-lead isotopes in sulfide minerals are important geochemical tracers in the earth sciences. However, in situ analyses of PGEs and S–Pb isotope compositions in natural sulfides using laser-ablation (multicollector) inductively coupled plasma mass spectrometry (LA-(MC)-ICP-MS) are limited by a lack of suitable sulfide reference materials. A new synthetic method to produce sulfide reference materials was reported in this study. The hydrothermal synthesis technique was used to prepare the initial nano-FeS₂ particles. Trace elements were added to the reaction medium and then entered into the lattice of the nano-FeS₂ particles during the crystal growth process. The powder-pressed pellets prepared by the nano-FeS₂ particles (500–600 nm) exhibited excellent cohesion and were suitable for laser ablation microanalysis. Using this method, we synthesized four sulfide reference materials with different mass fractions of trace elements. Repeated measurements using LA-(MC)-ICP-MS demonstrated good homogeneity for most of the trace elements (RSD <3% for PGEs, Au and Pb) and S isotope compositions (<0.23‰, 2SD) in the four sulfide reference materials, and Pb isotope compositions in two of these materials (<0.06% and <0.17%, 2RSD). Four sulfide reference materials were used as external standards to certify two commercial sulfide standards, MASS-1 and STDGL3#35. Accurate results from the analysis for trace elements were obtained, indicating that the synthesized sulfide reference materials are appropriate matrix-matched materials available for calibration in sulfides using LA-ICP-MS. The results also indicated that the hydrothermal synthesis of the nanoparticles can serve as a potentially effective approach for the preparation of microanalysis reference materials.