The complex and indeterminant composition of NOM makes characterization of its redox activity challenging. Approaches that have been taken to address these challenges include chemical probe reactions, potentiometric titrations, chronocoulometry, and voltammetry. Electrochemical methods can be diagnostic, quantitative, and complementary, but their application to NOM requires extensive optimization and validation. A historical perspective on the development of this field will be provided, starting with efforts in the 1980s by colleagues of George Aiken at the U.S. Geological Survey and Colorado School of Mines. More recent developments have improved the resolution of electrochemical characterizations of NOM, so it is now possible to address more subtle questions regarding its redox properties. For example, the range of peak potentials resolved by voltammetry spans most of the redox potentials obtained by other means that have been reported for various types of NOM or NOM model compounds. The multiplicity of electron-transfer steps that are distinguishable by voltammetry, and the likelihood that there is a degree of redox-coupling among these moieties, suggests that the redox potential of NOM might best be modeled as a continuum of redox potentials. The kinetics of electron exchange along this continuum will vary with factors such as the complex tertiary structure of NOM. The tertiary structure of NOM is likely to impact its redox activity at mineral-water (or microbe-water) interfaces, which is an issue we have recently begun to investigate.

Electrochemical characterization of natural organic matter and its role as an electron transfer mediator in biogeochemical process

253rd National Meeting (2017)

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