Liquid chromatography/mass spectrometry stable isotope analysis of dissolved organic carbon in stream and soil waters.

A commercial interface coupling liquid chromatography (LC) to a continuous-flow isotope ratio mass spectrometry (CF-IRMS) instrument was used to determine the δ(13) C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were studied. Based on wet chemical oxidation of dissolved organics the LC/IRMS interface allows the on-line injection of small volumes of water samples, an oxidation reaction to produce CO(2) and gas transfer to the isotope ratio mass spectrometer. In flow injection analysis (FIA) mode, bulk DOC δ(13)C analysis was performed on aqueous samples of up to 100 μL in volume in the range of DOC concentration in fresh waters (1-10 mg C.L(-1)). Mapping the DOC δ(13)C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate analyses) with little sample manipulation. The relative contributions of different plot sectors to the DOC pool in the stream draining the plot were tentatively inferred on the basis of δ(13)C differences between the hydrophilic and hydrophobic components.