A toc system for the analysis of the d13c signature of estuarine and marine dissolved organic carbon

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The stable isotope composition of dissolved organic carbon (d13C-DOC) provides powerful information towards understanding carbon sources and cycling, but analytical limitations have precluded its routine measurement in natural estuarine and seawater samples. The methods employed to measure d13C-DOC in marine samples tend to be long and tedious usually requiring highly specialized, expensive equipment, large sample volumes, and a number of steps to remove carbonates and quantitatively convert DOC into CO2 for eventual off-line analysis by mass spectrometry. Recent interfacing of wet oxidation-based dissolved organic carbon analyzers and isotope ratio mass spectrometers has simplified the measurement of d13C-DOC in freshwaters, but the analysis of salty estuarine/marine samples still proves difficult. We have successfully coupled the a high-temperature catalytic oxidation-based total organic carbon analyzer to an isotope ratio mass spectrometer (HTC-IRMS) through cryogenic trapping of analyte gases exiting the HTC analyzer for routine analysis of d13C-DOC in estuarine and marine samples (Panetta R.J., Ibrahim M., Gélinas, Y. (2008) Anal. Chem. 80, 5232-5239). We are one of the very few laboratories in the world currently capable of routinely measuring samples over the natural range of DOC concentrations (from 35 µM to over 2000 µM), and salinities (<0.1 to 36 g/kg) encountered in the environment, with excellent d13C-DOC accuracy (± 0.2 per mil) and precision (± 0.3 per mil).