Carbon and hydrogen isotope fractionation of acetic acid during degradation by ultraviolet light

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Low molecular-weight carboxylic acids, such as acetic and propionic acids, are abundant organic compounds in carbonaceous chondrites, and are generally enriched in heavy stable isotopes (i.e., ¹³C and D) relative to terrestrial organic compounds. In this study, we have determined carbon and hydrogen isotopic fractionation of acetic acid, and site-specific carbon isotopic fractionation of acetic acid, during degradation by ultraviolet (UV) light. Acetic acid became enriched in ¹³C and D with increased UV exposure times. The isotopic fractionation factors (α) of total, methyl and carboxyl carbon of acetic acid were 0.9922, 1.0022 and 0.9823 respectively, and the α value for hydrogen was 0.9875. These results suggest that UV degradation could be a process for yielding ¹³C- and D-enrichment of acetic acid in natural environments.