Accurate determination of sulfur, selenium and tellurium in geological reference materials by isotope dilution inductively coupled plasma-tandem mass spectrometry (ID-ICP-MS/MS)

Abstract

Sulfur (S), selenium (Se) and tellurium (Te), characterized by their chalcophile, siderophile and volatile properties, are increasingly critical in geoscience and planetary research. However, efficient and high-precision quantification of S–Se–Te in rocks remains analytically challenging due to severe spectral interferences, ultralow abundances, and potential volatile losses. In this study, a novel isotope dilution-inductively coupled plasma tandem mass spectrometry (ID-ICP-MS/MS) method was developed. Potential elemental volatile losses were addressed by isotope dilution, while the spectral interferences of S–Se–Te were suppressed online with N₂O or O₂ as reaction gases, eliminating the need for complicated chemical purification or hydride generation typically required by conventional methods. Interference-free measurements were performed by systematic investigation of reaction gas flow rate and ion kinetic energy (controlled by the octopole bias voltage). S and Se were mass-shifted to their oxide species for analysis, resulting in a substantial reduction of both background signals and interference signals compared to the single-quadrupole mode. Te was measured in “on-mass” mode, and the background equivalent concentrations from geological matrices for both Se and Te reached ppt levels. Isotope ratio precision and accuracy were enhanced through further optimization of integration times and mass bias correction strategies. Outstanding method detection limits of <0.29 ng mL⁻¹ for S, <0.0017 ng mL⁻¹ for Se, and <0.0033 ng mL⁻¹ for Te were achieved. Both N₂O and O₂ modes demonstrated good agreement with conventional ID-ICP-MS results across geological reference materials. This method simplifies sample preparation, enables high-precision and high-throughput analysis, and has great application potential for geochemical studies.