Abstract

5,10,15,20-tetrakis-tetraferrocenylporphyrin (TFcPH(2)) free ligand was synthesized and characterized by spectroscopic (UV-Vis, (HNMR)-H-1, FT-IR) and electrochemical (cyclic voltammetry) techniques. The electrocatalytic oxidation of S(IV) species in aqueous media mediated by two modified electrodes was studied. In both cases, tetraferrocenylporphyrin was used to modify electrodes. Glassy carbon electrode was modified by drying-drop method, whereby a drop of concentrated solution (approximate to 10(-4) M) of the porphyrin was applied to the electrode surface and allowed to dry (DDE electrode), and carbon-paste was modified with solid porphyrin (CPE electrode). DDE electrode shows electrocatalytic activity toward the sulfite oxidation only for one cycle. Loss of activity of this modified electrode was attributed to the formation of a stable adduct between the porphyrin and the product of the oxidation of sulfite. However, TFcPH(2) absorbed on glassy carbon electrodes shows electrocatalytic activity toward the sulfite reduction in acid media. The catalytic current peak was linearly dependent on the sulphite concentration over concentration 0.03 - 1.4 mM, and the detection limit is 22 mu M under optimized conditions.