ELECTROCATALYSIS OF ASCORBIC ACID ON THE GLASSY CARBON ELECTRODE CHEMICALLY MODIFIED WITH POLYANILINE FILMS.

Chemically modified electrodes prepared by electropolymerization of aniline on glassy carbon electrodes, exhibited good electrocatalytic properties towards ascorbic acid oxidation. The electrocatalytic response was evaluated by cyclic voltammetry with regard to pH, Blm thickness, ascorbic acid concentration, scan rate, electrolyte composition, rotation speeds of the electrode, and other variables. The location of the reactions taking place was discussed with experimental evidence that the cross-exchange reaction is the rate-determining step. Experiments in flowing streams were performed to characterize the electrode as an amperometric sensor for the determination of ascorbic acid. The electrode stability, precision, limit of detection and linear range were evaluated at a constant potential of 0.350 V (vs. Ag/AgCl). The limit of detection was 1.0 mu M (i.e., 1.76 ng injected), and the calibration plot was linear in the range 1.0 mu M-0.7 mM (correlation coefficient 0.999). The resulting modified electrode was found to retain 80 % of its initial response in flowing streams for 8 h of operating time