MECHANISTIC STUDIES OF THE ELECTROCATALYTIC OXIDATION OF NADH AND ASCORBATE AT GLASSY-CARBON ELECTRODES MODIFIED WITH ELECTRODEPOSITED FILMS DERIVED FROM 3,4-DIHYDROXYBENZALDEHYDE

Studies of the electrocatalytic oxidation of beta-nicotinamide adenine dinucleotide (NADH) at glassy carbon rotated disk electrodes modified with electrodeposited films derived from 3,4-dihydroxybenzaldehyde (3 ,4-DHB) indicate that the mechanism of such electrooxidation proceeds via the formation of an intermediate complex. The reaction also appear s to be strongly influenced by the presence of Ca2+ and Mg2+ ions as w ell as by pH. Ascorbate can also be electrocatalytically oxidized at t hese modified electrodes, giving rise to an electrochemical response v ery similar to that obtained for NADH, Due to this similarity, the pre sence of ascorbate in NADH determinations presents a severe interferen ce that cannot be mitigated on the basis of electrochemical responses alone, However, this interference effect can be virtually suppressed b y the presence of ascorbate oxidase in solution or immobilized on a ny lon mesh which, in turn, is in contact with the electrode modified wit h the film of 3,4-DHB. Using this approach, we describe the constructi on of an alcohol biosensor based on alcohol dehydrogenase and which is , furthermore, free from interference effects due to ascorbate.