THE DEVELOPMENT OF A PEROXIDASE BIOSENSOR FOR MONITORING PHENOL AND RELATED AROMATIC-COMPOUNDS

The possibility of horseradish peroxidase (HRP) modified solid graphite and carbon paste electrodes to perform as biosensors for the determination of phenol and related compounds was studied. Phenoxy radicals, farmed during the enzymatic oxidation of phenolic compounds in the presence of hydrogen peroxide, are reduced electrochemically. The reduction current is proportional to their concentration in the solution. From the hydrodynamic voltammograms, calibration curves and performance stability it was concluded that the reduction of phenoxy radicals is more efficient at the solid graphite electrodes in comparison with the carbon paste based sensor. The potentials, at which electrochemical reduction of phenoxy radicals appears, depend on the electron donating properties of the substituent in the phenol molecule. It was found that, in the presence of 10-20 mu M of H2O2 in the solution, the responses of HRP-modified solid graphite electrode to p-cresol are rate limited by the enzymatic reaction. The electrode was most stable when the buffer solution contained 5% of methanol. Among 20 phenolic compounds tested, phenol, catechol, resorcinol, p-cresol, 4-chlorophenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, vanillin and 2-amino-4-chlorophenol can be determined. The greatest sensitivity was obtained for 2-amino-4-chlorophenol (85 nA cm(-2) mu M(-1)).