A Mechanistic Study of High-Temperature Oxidation of Organic Carbon in Carbon Analyzers

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The mechanistic aspects of the oxidation of dissolved organic carbon (DOC) in high temperature combustion (HTC) carbon analyzers are largely unknown. For example, it is not known whether 02(g) is needed to oxidize DOC, whether "catalysts" are needed at all, or whether carbonaceous impurities in catalysts contribute significantly to system blanks. Until the situation changes, HTC analyzers will continue to be designed and used in an empirical manner. This research will test the hypothesis that oxidation of DOC in HTC instruments is largely due, in a mechanistic sense, to the reaction of DOC with hydroxyl radicals (OH) and other reactive species that are generated by thermal homolysis of injected H20. This hypothesis is amenable to direct experimental investigation. A commercial HTC carbon analyzer will be modified extensively and interfaced with several specialized instruments (e.g. gas chromatograph; gas chromatograph-mass spectrometer) that are used to quantify major and minor gaseous species that may form during analysis of a DOC sample. The compositions of carrier gases and catalysts will be varied systematically to clearly resolve the roles of 02(g) and OH in the oxidation process. Temperature- programmed volatization/combustion will be evaluated as a means of measuring inorganic carbon, volatile organic carbon, and non- volatile organic carbon. A new generation, mechanistically based HTC carbon analyzer will be designed and tested.