| Abstract
| - In this study, cyclic voltammetry was used to characterizethe redox properties of natural organic matter (NOM).Using a stationary platinum working electrode, minimalconcentrations of electrolyte, and dimethyl sulfoxide (DMSO)as the solvent, we were able to resolve two pairs ofoxidation and reduction peaks for a fraction of GeorgetownNOM that is enriched in polyphenolic moieties (NOM-PP). Applying our method to other fractions of GeorgetownNOM, and to samples of NOM from a wide range ofother sources, gave cyclic voltammograms (CVs) thatgenerally contained fewer distinguishing features than thoseobtained with NOM-PP. For comparison, CVs were alsoobtained using our method on six quinone modelcompounds: anthraquinone-2,6-disulfonate (AQDS),lawsone, juglone, menadione, menaquinone-4, andubiquinone-5. The CVs of these quinones were similar inshape to the CV of NOM-PP, consistent with the notion thatquinones are the dominant redox-active moieties associatedwith NOM. Quantitative analysis of the peaks in theseCVs showed that the peak potentials (Ep) were separatedby more than 0.059 V and that the peak currents (ip)were linearly related to the square root of the scan rate(v0.5) and concentration (C) for both NOM-PP and the modelquinones. Equivalent results were obtained with arotating Pt disk electrode. From this we conclude that NOM-PP and the model quinones undergo similar sequencesof two one-electron, quasi-reversible, diffusion controlled,electron transfers at the Pt electrode surface in DMSO.Although it is difficult to relate these results to Nernstianstandard potentials vs the standard hydrogen electrode(SHE) under aqueous conditions, it is clear that the apparentformal potential for NOM-PP lies between the correspondingpotentials for menadione and juglone and well abovethat of AQDS. Attempts to derive correlations between Epand ip for the NOMs with quantifiable electrode responseand other measurable properties of NOM (including tracemetal content and UV−vis absorbance) did not yieldany strong relationships.
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