A fluorination method for measuring the C- C isotopologue of C molecules.

Rationale: Doubly substituted isotope species ("clumped" isotopes) can provide insights into the biogeochemical history of a molecule, including its temperature of formation and/or its (bio)synthetic pathway. Here, we propose a new fluorination method for the measurement of C- C species in C molecules using a conventional isotope ratio mass spectrometer. Target molecules include ethane, ethene and ethanol.

Methods: C- C isotope species in C molecules were measured as C F using a conventional isotope ratio mass spectrometer. Ethane and ethene are directly fluorinated to C F . Ethanol is measured after dehydration to ethene and subsequent fluorination of the latter. The method enables the measurement of the Δ C C values normalized against a reference working standard.

Results: The reproducibility of the whole protocol, including chemical modification steps and measurement of C F isotopologues, is better than ±0.14‰ for all the compounds. Ethane from natural gas samples and biologically derived ethanol show a narrow range of Δ C C values, varying from 0.72‰ to 0.90‰. In contrast, synthetic ethanol as well as putative abiotic ethane show Δ C C values significantly different from this range with values of 1.14‰ and 0.25‰, respectively.

Conclusions: The method presented here provides alternative means of measuring C- C species to that using high-resolution mass spectrometry. Preliminary data from natural and synthetic molecules re-emphasizes the potential of C clumped isotope species as a (bio)marker.