Electrooxidation and determination of sulfite in ethanol–water solutions using poly-Cu(II)-tetrakis(x-aminophenyl)porphyrin/glassy carbon modified electrodes

Abstract

A comparison is made of the behavior of three Cu(II)-porphyrins (with the amino substituents in different positions on the periphery of the ligand) electropolymerized on glassy carbon electrodes in HCl as solvent. The electropolymerized films show a certain degree of demetallation but the Cu amount of porphyrin in each case is sufficient to catalyze the oxidation of sulfite and hydrogensulfite in ethanol–water solutions. The ligands of the porphyrins are almost inactive in the electrocatalysis of the sulfite. The oxidation processes are favored at low scan rates. The foot of the oxidation waves depends on the positions. The most active porphyrin bears the substituents with the amino groups in para position, the oxidation occurring at low positive potentials. All the modified electrodes can be used as amperometric sensors for sulfite; they show linear relationships between the current and sulfite concentration in the range in which sulfites are present in red wines. The modified electrodes are stable and all of them promote the oxidation of sulfite to sulfate.