The mechanism of the electrochemical oxidation of p-coumaric acid on a glassy carbon electrode was investigated using cyclic, differential pulse, and square wave voltammetry at different pHs. The oxidation of p-coumaric acid is irreversible over the whole pH range. After successive scans, the p-coumaric acid oxidation product deposits on the electrode surface, forming a polymeric film that undergoes reversible oxidation at a lower potential than p-coumaric acid. This polymeric film increases in thickness with the number of scans, covering the electrode surface, and impeding the diffusion of the p-coumaric acid and its oxidation on the electrode. The oxidation of p-coumaric acid is pH dependent up until values close to the pKa. For pHs higher than pKa, the p-coumaric acid oxidation process is pH independent. An electroanalytical determination procedure of p-coumaric in pH 8.7 0.2 M ammonium buffer was developed, and a detection limit, LOD=83 nM, and the limit of quantification, LOQ=250 nM, were obtained.
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