Amperometric detection of phenols using peroxidase-modified graphite electrodes

This report describes the development of the new concept utilising various peroxidases for determination of phenolic compounds in flow injection (FI) mode. A solid graphite electrode was modified with peroxidase (EC 1.11.1.X) and used in an amperometric detection system. At the peroxidase electrode phenolic compounds can be oxidised in the presence of hydrogen peroxide (H2O2). The phenoxy radicals formed during the enzymatic oxidation can be reduced back electrochemically at -50 mV vs. Ag/AgCl. This reduction current is proportional to the concentration of the phenolic compound. Different methods of coupling horseradish peroxidase (HRP, EC 1.11.1.7) were tested, including adsorption and covalent immobilisation. It was found that the best electrodes gave a detection limit for p-cresol of 0.4 mu M (using 60 mu M H2O2 in the flow carrier). Peroxidases of different biological origins were adsorbed to graphite electrodes and the selectivity of these electrodes was studied for eight phenolic compounds. All the peroxidase electrodes in the experiment, except the chloroperoxidase electrode, were sensitive to all the phenolic compounds tested.