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

高温燃烧(HTC)碳分析仪中溶解有机碳(DOC)氧化的机理在很大程度上是未知的。例如，是否需要02(G)来氧化DOC，是否需要“催化剂”，或者催化剂中的含碳杂质是否对系统空白有重大影响，目前尚不清楚。在情况发生变化之前，HTC分析仪将继续以经验的方式设计和使用。这项研究将检验这一假设，即在HTC仪器中DOC的氧化在很大程度上是由于DOC与注入的H20热均解产生的羟基自由基(OH)和其他活性物种的反应。这一假设可以用来指导实验研究。商业HTC碳分析仪将进行广泛的改装，并与几种专门的仪器(例如，气相色谱仪；气相色谱-质谱仪)对接，用于对DOC样品分析过程中可能形成的主要和次要气体物种进行量化。将系统地改变载气和催化剂的组成，以明确02(G)和OH在氧化过程中的作用。程序升温挥发/燃烧将作为一种测量无机碳、挥发性有机碳和非挥发性有机碳的手段进行评估。将设计和测试新一代基于机械的HTC碳分析仪。

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.