A Novel Strategy for Synthesizing Matrix-Matched Microanalysis Reference Materials via Hydrothermal Precursors and Ultrahigh-Pressure Sintering

Secondary-ion mass spectrometry (SIMS) and related in situ microanalytical techniques allow precise chemical and isotopic characterization at micron and submicron scales, providing insights into spatially heterogeneous processes. However, the quantitative accuracy of SIMS is limited by matrix effects, which cause instrumental mass fractionation (IMF) between measured and true isotope ratios. Accurate quantification requires matrix-matched reference materials (RMs) with identical physical and chemical properties to the unknown samples. Most existing SIMS RMs are derived from natural minerals, which often exhibit heterogeneity, limiting reproducibility and interlaboratory comparability. Synthetic RMs offer a promising solution, but their development for SIMS has been challenging due to the sensitivity of SIMS to microstructural attributes such as surface smoothness and grain size. This study presents a novel synthesis strategy for producing matrix-matched pyrite (FeS2) RMs. By combining hydrothermal precursor synthesis with low-temperature ultrahigh-pressure (UHP) sintering, we fabricated dense, nanocrystalline pyrite ceramics with controlled stoichiometry and exceptional sulfur-isotope homogeneity. The resulting material exhibited sputtering behavior indistinguishable from that of natural pyrite, demonstrating the strategy as a robust framework for producing synthetic sulfide RMs. This approach facilitates the improvement of analytical accuracy and reproducibility in microanalytical science and can be extended to other mineral systems.