ELECTROCHEMICAL OXIDATION OF L-ASCORBIC-ACID AT THE GRAPHITE ELECTRODE AND ITS MONITORING BY A THICK-FILM GRAPHITE SENSOR ASSEMBLY

The experimental results obtained in this study show that a thick-film graphite sensor assembly (with a Pt counter and an Ag/AgCl reference electrode) can be conveniently fabricated by the photolithographic and screen-print metallization techniques. This sensor has been successfully employed for quantitatively determining L-ascorbic acid concentration in aqueous solutions with reasonably good reproducibility. This sensor provides the possibility of developing a miniature size practical device for detecting ascorbic acid in biochemical processing, such as in food and drug production. The mechanistic aspects of the oxidation of L-ascorbic acid on optical pyrolytic graphite electrodes were further studied with a rotating OPG disk electrode in two different electrolyte solutions. It was found that the oxidation of L-ascorbic acid is more favored in pH = 7 solutions than in pH = 1 solutions although a common 2-electron transfer pathway is applied in both cases.