A Unified Method for Triple Oxygen Isotope Analysis of Sulfate, Water, and Organics

Triple oxygen isotope analyses of sulfate, water, and organic materials provide vital insights into geochemical processes. Here, we present the fully automated TORCH method (Triple Oxygen isotope analysis using Reduction, Conversion, and High-precision laser spectroscopy), which enables the direct normalization of various materials to the VSMOW-SLAP reference scale using a unified method. The method integrates high-temperature thermal conversion elemental analysis (TC/EA), high-voltage glow discharge CO-to-CO₂ conversion, and tunable infrared laser direct absorption spectrometry for simultaneous δ¹⁸O and Δ'¹⁷O determination from CO₂. We applied the TORCH method to international and in-house standards of Barite (IAEA-SO-5, IAEA-SO-6), benzoic acid (IAEA-601), cellulose (Sigma-Aldrich 0742213, labeled Cellulose-KOSI), and water (VSMOW2, SLAP2, USGS46), demonstrating quantitative oxygen yields and a reproducibility reaching ±14 per meg for Δ'¹⁷O and ±0.3‰ for δ¹⁸O (1 SD). We show that consistent triple oxygen isotope values across different sample types and analytical techniques are achieved when quantitative oxygen extraction and accurate scaling are assured. The TORCH method delivers flexibility across varied matrices, paving the way for high-accuracy triple oxygen isotope analysis of geologically and environmentally relevant sample types.