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 Delta S-33 (not Delta S-36) by a low precision SO2 method indicating the occurrence of anomalous fractionation in S-33. The photolysis of PPS in micellar solution produced MIF of S-33 in residual PPS ranging from depletion by -2.1 parts per thousand to enrichment by 6.4 parts per thousand, with small mass-dependent fractionation of delta S-34 up to 2.1 parts per thousand. While this magnitude of S-33 anomaly is comparable to the range of values observed in Archean rocks, no anomaly in S-36 was detected for the S-32-S-34-S-36 system beyond analytical precision (0.19 parts per thousand). These results confirm the anomalous fractionation to be caused most likely by magnetic isotope effects (MIE), affecting only the nuclear spin possessing S-33 among the four stable isotopes of sulfur. The observed initial depletion of S-33 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 S-33 abundance. (C) 2012 Elsevier Ltd. All rights reserved.