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

Abstract

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. Copyright © 2007 by The Geochemical Society of Japan.