Quantitative and Specific Recovery of Organic and Mineral Sulfur for Multi-isotope Analysis

Sulfur is a key element of biogeochemical cycles, being both an essential component of living cells and involved in major geological processes. Its four stable isotopes (32S, 34S, 33S, 36S, in order of abundance) are subject to equilibrium and kinetic fractionations, which can be used as tracers to understand sulfur cycling processes. Multi-isotope studies noticeably revealed mass-independent fractionation processes of 33S and 36S, enlightening previously unknown specific organic or inorganic (bio)(geo)chemical mechanisms. Though the analytical procedures for the determination of S-multi-isotope compositions, which requires a quantitative extraction and purification of sulfur, are well-known for mineral sulfur species, the existing procedures for the extraction of organic sulfur are either restricted to specific species or technically restrictive. Here we propose a new chemical procedure for the quantitative recovery of organic sulfur in the form of Ag2S, for multi-isotope analysis, which is also compatible with the multi-isotope analysis of inorganic sulfur species from the same samples. This procedure is based on a standard sequence of reductive attacks specific of mineral sulfur species and was validated on various samples including fresh sediments, source rocks and oils.