Horseradish Peroxidase Immobilized Electrode for Phenothiazine Analysis

A horseradish peroxidase (HRP) immobilized carbon composite electrode has been developed for the amperometric study of phenothiazine analogues. Flow injection analysis and batch experiments have been realized in acetate buffer in the presence of hydrogen peroxide. Cyclic voltammetry and amperometry using a thin-layer flow cell (dual configuration, serial mode) have permitted one to suggest the mechanisms governing the biosensor signal at -0.1 V (vs. Ag/Ag+), in the presence of hydrogen peroxide, by addition of a phenothiazine derivative. It was inferred that electron transfer mediation by the phenothiazine occcurred at HRP/graphite adsorbed sites, in addition to peroxidation by dispersed HRP with substrate recycling at the graphite array-like structure of the biosensor. Thanks to these processes, high sensitivities were achieved especially in batch configurations, with amperometric detection capabilities down to 10-8 M in acetate buffer pH 4.7. Application of the biosensor to the determination of phenothiazines in drug formulations were realized.