THE KINETICS OF SIMULTANEOUS CONVERSION OF HYDROGEN-PEROXIDE AND AROMATIC-COMPOUNDS AT PEROXIDASE ELECTRODES

The cathodic reduction of hydrogen peroxide by horse-radish peroxidase immobilized at graphite electrodes can be activated by p-aminophenol, 3,3',5,5'-tetramethylbenzidine, N-acetyl-p-aminophenol and p-hydroxydiphenyl. At pH 7.0, at an electrode potential of 0.0 or 0.1 V, a rotation rate 1000 min-1 and a hydrogen peroxide concentration of 30-mu-M, an electrode response was reached of 2.4-12.2 mu-A/cm2 per mu-M activator concentration. Uric acid, luminol and ABTS can also be used to activate the cathodic current, but then the activation is slower and the electrode sensitivity is 1.1-100-mu-A/mM cm2. The activated current depends on activator diffusion and the process proceeds at an electrode potential lower than the potential of redox conversion of the activator. The suggested kinetic scheme includes enzymatic oxidation of the activators and electrochemical reduction of their oxidized forms.