Measurement of dissolved organic carbon by wet chemical oxidation with persulfate: influence of chloride concentration and reagent volume

The influence of chloride content and reagent volume on the analysis of dissolved organic carbon by wet chemical oxidation with persulfate was evaluated. A strong hyperbolic relationship was found between measured DOC concentration and volume of persulfate added for oxidation in both marine and artificially chlorinated (NaCl) freshwater samples. Freshwater samples showed no such relationship. Precision of measured DOC concentrations averaged 4–7% and did not vary as a function of persulfate volume. Apparently chloride, and possibly other ions, produce significant interference in the oxidation reaction of organic matter by persulfate. Thus, analysis of DOC in seawater, or water with a high chloride content, by persulfate oxidation may yield erroneously low, yet precise, results if asymptotic concentrations of persulfate are not employed. Use of less than asymptotic concentrations of persulfate may account for some of the variability encountered in intercomparison experiments employing persulfate and high temperature catalytic oxidation methods.