LC/MS 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 spectrometer (IRMS) was used to analyse δ 13 C of dissolved organic carbon (DOC) in natural waters. Stream and soil waters from a farmland plot in a hedgerow landscape were selected for application. Based on wet chemical oxidation of dissolved organics the LCIRMS interface allows on-line injection of small volumes of water samples, oxidation reaction to produce CO2 and gas transfer to the IRMS. In flow injection analysis (FIA) mode, bulk DOC δ 13 C analysis was performed on up to 100 μL aqueous sample in the range of DOC concentration in fresh waters (1-10 mg C.L -1 ). Mapping DOC δ 13 C spatial distribution at the plot scale was made possible by this fairly quick method (10 min for triplicate) 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 hydrophilic and hydrophobic components.