Sulfur mass-independent fractionation in liquid phase chemistry: UV photolysis of phenacylphenylsulfone as a case study

The sulfur isotope mass-independent fractionation (S-MIF) represents a distinct geochemical signature commonly observed in Archean rocks. Although S-MIF is generally thought to be exclusive to gas phase chemistry, several studies have suggested that liquid phase or heterogeneous chemistry may also produce S-MIF signatures.This study investigates the potential contribution of the poorly explored mass-independent effects from liquid phase sulfur chemistry. Our investigation focused on laboratory experiments of the UV photolysis of phenacylphenylsulfone as a model system. This system was chosen due to previous measurements of Δ33S (not Δ36S) by a low precision SO2 method indicating the occurrence of anomalous fractionation in 33S.The photolysis of PPS in micellar solution produced MIF of 33S in residual PPS ranging from depletion by −2.1‰ to enrichment by 6.4‰, with small mass-dependent fractionation of δ34S up to 2.1‰. While this magnitude of 33S anomaly is comparable to the range of values observed in Archean rocks, no anomaly in 36S was detected for the 32S–34S–36S system beyond analytical precision (0.19‰). These results confirm the anomalous fractionation to be caused most likely by magnetic isotope effects (MIE), affecting only the nuclear spin possessing 33S among the four stable isotopes of sulfur. The observed initial depletion of 33S in the reactant PPS was unexpected and suggests changing contributions of at least two spin-selective processes. The results of this study demonstrate that liquid phase processes, such as the photolysis of certain organic sulfur compounds, can produce anomalous 33S abundance.