A kinetic study of the electrocatalytic oxidation of reduced glutathione at Prussian blue film-modified electrode using rotating-disc electrode voltammetry

In this work a thorough study of the oxidation of reduced glutathione (GSH) by electro-generated Berlin Green (BG) at Prussian blue (PB) film-modified glassy carbon electrode (GCE) was attempted by employing cyclic voltammetry (CV) and rotating-disc electrode (RDE) techniques. It has been shown that oxidation of GSH occurs at the potential coinciding with that of FeII(CN)6 to FeIII(CN)6 transformation in the PB film, where no oxidation signal is observed at a bare GCE. The kinetics of catalytic reaction was investigated using a rotating-disc electrode voltammetry. The results obtained for various thicknesses of film and GSH concentrations are explained using the theory of electrocatalytic reactions at chemically modified electrodes (Andrieux–Saveant model) and it was concluded that the reaction has a “surface” reaction mechanism in which a few monolayers at film/solution side engaged in the catalytic process. However, the “surface” reaction tends to a saturation limit with increasing GSH concentration was observed and the behavior has been explained by using Michealis–Menten inner sphere kinetics. Tafel plots for various concentrations of GSH have been drawn and the slope values of 95–110 mV/decade indicate that the first electron transfer is not rate limiting process. The reaction order with respect to GSH and H+ were calculated as 0.6 and −0.4, respectively.