Carbon paste electrodes modified with a new phenothiazine derivative adsorbed on zeolite and on mineral clay for NADH oxidation

Two new composite electrodes, based on carbon paste (CP) incorporating a synthetic zeolite (13X type; Z) or a natural mineral clay (bentonite; B), both impregnated with a new phenothiazine derivative [3,7-di(m-aminophenyl)-10-ethyl phenothiazine; EPh], were developed. The physical properties of the EPh-Z and EPh-B composite materials have been investigated using scanning electron microscopy, energy dispersive X ray spectroscopy, Fourier transform infrared spectroscopy. Cyclic voltammetry (CV) and rotating disk electrode measurements were used for electrochemical characterization of the EPh-Z-CPEs and EPh-B-CPEs electrodes. CV measurements revealed a reasonably fast electron transfer rate for both modified electrodes. No significant differences, concerning the pH effect on the formal standard potential, the magnitude of the rate constants for heterogeneous electron transfer and the electrode response stability, were observed between the investigated electrodes. Both electrodes showed a good electrocatalytic activity for β-nicotinamide adenine dinucleotide (NADH) oxidation (for example, in the case of EPh-Z-CPEs the electrocatalytic rate constant was 1.1 × 104 M−1 s−1, at pH 7).