A persulfate oxidation method for stable isotope analysis of dissolved organic carbon and the influence of inorganic ions on the results

Abstract

The stable carbon isotope ratio of dissolved organic carbon (δ13CDOC) is a powerful indicator in earth and environmental sciences. In the present study, a simple and fast method was developed for measuring δ13CDOC values using persulfate oxidation and gas chromatography–isotope ratio mass spectrometry (GC/IRMS). The δ13CDOC values in standards and environmental water samples with dissolved organic carbon concentrations between 1 and 30mg/L were measured precisely and accurately with this technique. The measurement precision was <0.50‰ for samples containing 6.3μg or more of carbon, and 1‰ for samples containing 3.5μg of carbon. The reproducibility for multiple preparations was ±0.50‰. The results showed that chloride and other inorganic ions commonly present in environmental waters (K+, Na+, Ca2+, Mg2+, NH4+, Cl−, NO3− and SO42−) did not influence the δ13CDOC measurement when present in low concentrations. Because the GC/IRMS is multifunctional and not sensitive to water vapor, it is particularly appropriate for laboratories that lack other specialized instruments.