Electrochemical Analysis of Beverage Phenolics Using an Electrode Modified With Poly(3,4-ethylenedioxithiophene)

An electroactive layer of poly(3,4-ethylenedioxithiophene) (PEDOT) was electropolymerised on to a glassy carbon electrode and used to characterise phenolics in diluted tea and coffee samples. There were two oxidation peaks in the voltammograms of green tea at around 190 mV and 290 mV (Ag/AgCl, pH 5.5) which matched the response of epigallocatechin gallate (EGCG), the principle phenolic present in green tea. The first of these two peaks was less prominent in those black teas that had a low content of EGCG, as determined by HPLC. The voltammetric response of coffee samples resembled that of chlorogenic acid, the major phenolic present. The anodic peak area to 500 mV was used to estimate the total phenolic content of the samples due the strongest reducing agents, and the values were smaller than those obtained using the Folin Ciocalteu assay. The PEDOT electrode proved to be effective in providing superior peak separation, compared to glassy carbon electrodes, and to show an enhanced current response due to pre-adsorption of the phenolics.