Gas chromatography-pyrolysis-isotope ratio mass spectrometry: a new method for investigating intramolecular isotopic variation in low molecular weight organic acids

A new GC-Pyrolysis-IRMS method was developed for the delta(13)C determination of carboxyl carbon in low-molecular weight organic acids. By utilizing a palladium-wire reactor Lit 600 C with a helium,hydro-g-en 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 delta(13)C values at natural abundance levels, As a demonstration of this ne capability, the carboxyl carbon Of low-molecular weight (LMW, C-2-C-6) organic acids generated via hydrous pyrolysis of an oil-prone source rock (the Ghareb Shale) shows delta(13)C values consistent with the hypothesis that organic acids readily undergo exchange of their carboxy I carbon with aqueous inorganic carbon. (C) 2002 Elsevier Science Ltd. All rights reserved.