A new GC-Pyrolysis-IRMS method was developed for the δ13C determination of carboxyl carbon in low-molecular weight organic acids. By utilizing a palladium-wire reactor at 600 °C with a helium/hydrogen reactant gas, the carboxyl carbon of low-molecular weight organic acids is pyrolytically cleaved and introduced into an IRMS for stable carbon-isotope analysis. The precision of the GC-Py-IRMS method is similar to that of more conventional, combustion-based continuous-flow IRMS techniques and interpretation of isotope-dilution experiments with acetic and octanoic acid shows that the technique is sufficiently accurate for the determination of δ13C values at natural abundance levels. As a demonstration of this new capability, the carboxyl carbon of low-molecular weight (LMW, C2-C6) organic acids generated via hydrous pyrolysis of an oil-prone source rock (the Ghareb Shale) shows δ13C values consistent with the hypothesis that organic acids readily undergo exchange of their carboxyl carbon with aqueous inorganic carbon.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology