Kaplan, L.A. 1992. Limnology and Oceanography 37:1119–1125.
I performed parallel measurements of dissolved organic C (DOC) concentrations in freshwaters with Pt-catalyzed, high-temperature and Pt-catalyzed persulfate oxidation methods. Checks on instrument precision, bias, inorganic C removal, and oxidation efficiency were included in the comparison. DOC concentrations generated by the two techniques agreed to within 10% or better when stream water, spring water, groundwater, soil water, and a commercial humic acid were analyzed. Persulfate catalytic oxidation underestimated the high-temperature catalytic oxidation technique by 3–6% on stream-water and soil-water samples. Incomplete oxidation of chemically recalcitrant molecules with the persulfate technique may account for these minor differences. Analyses of humic and fulvic acids isolated from stream water were used to demonstrate that 90–96% oxidation efficiency of heterogeneous, biologically recalcitrant organic acids can be achieved with persulfate catalytic oxidation. Precipitation of hydrophobic DOC, presumably humic acids, when freshwater samples are acidified to pH 2–3 and sparged externally to an analyzer to remove inorganic C can lead to the underestimation of DOC concentrations, which may be an important consideration when using the high-temperature oxidation method with blackwaters.