ELECTROCHEMISTRY OF ASCORBIC-ACID AT POLYPYRROLE DODECYL-SULFATE FILM-COATED ELECTRODES AND ITS APPLICATION

The electrochemical behaviour of ascorbic acid at both free-standing Polypyrrole/dodecyl sulphate (PPy/DS) films and PPy/DS-film-coated electrodes has been examined by voltammetry, rotating disk electrode experiments and chronoamperometry. The results indicate that the PPy/DS films reduce the overpotential of ascorbic acid oxidation. The anodic peak due to the oxidation of ascorbic acid occurred at about 0 V (vs. a saturated calomel electrode), which is at least 300 mV more negative than at the uncoated electrode. The oxidation process is independent of the electrode substrate and film thickness. Rotating disk electrode experiments revealed that the anodic current is controlled solely by the mass transport process in solution. The voltammetry of ascorbic acid with free-standing PPy/DS films suggests that the electron exchange reaction occurs at the PPy/DS film \ solution interface rather than at the substrate electrode. Furthermore, the PPy/DS films exhibited much lower background current and higher stability compared with PPy films prepared in inorganic anion solutions. The electrode has been applied successfully to the determination of ascorbic acid in single- and multivitamin tablets, with a recovery of 94%-107% and a relative standard deviation of 3.5%-5.0%.