Geochemistry, Geophysics, Geosystems (Jul 2020)
A Simple Elemental Sulfur Reduction Method for Isotopic Analysis and Pilot Experimental Tests of Symmetry‐Dependent Sulfur Isotope Effects in Planetary Processes
Abstract
Abstract Recent insights into fundamental mechanisms underlying quadruple stable sulfur isotope (32S, 33S, 34S, and 36S) mass‐independent fractionation (S‐MIF) chemistry and potential implications for planetary processes highlight the urgent need of conducting laboratory experiments to delineate the chemical physics of S‐MIF. Elemental sulfur (S0), a ubiquitous component in the atmospheres of early Earth and Mars, is a major product or reactant in most experiments. Developing different chemical protocols for isotopic analysis is consequently of utility. The reduction of S0 to hydrogen sulfide (H2S) is the first step of the fluorination method for isotopic analysis, but existing S0 reduction methods require relatively long chemical reagent preparation time. Here we present an operationally simple and rapid method for reducing S0 to H2S directly by “Thode solution.” External uncertainties of our method for δ34S, Δ33S, and Δ36S measurements (associated with reduction, fluorination, purification, and mass spectrometer analysis) are 0.3‰, 0.01‰, and 0.2‰, respectively, comparable with traditional methods. This new technique was used to determine quadruple stable sulfur isotope compositions of product S0 in a set of pilot experiments designed to investigate possible symmetry‐dependent isotope effects in planetary‐relevant elemental sulfur recombination reactions. Differences in Δ33S and Δ36S between initial and produced S0 are slightly larger than analytical errors, shedding new light into the role of sulfur recombination reactions in S‐MIF. Our study offers a practical approach for measuring multiple isotopic compositions of S0 in laboratory and natural samples and creates new opportunities for deepening understanding of S‐MIF signatures in Archean rocks and Martian meteorites.
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