ELECTROCATALYSIS OF ASCORBIC-ACID ION THE GLASSY-CARBON ELECTRODE CHEMICALLY-MODIFIED WITH POLYANILINE FILMS

Chemically modified electrodes prepared by electropolymerization of an iline on glassy carbon electrodes, exhibited good electrocatalytic pro perties 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, rota tion 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 electr ode stability, precision, limit of detection and linear range were eva luated 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 p lot 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 it s initial response in flowing streams for 8 h of operating time.