LASER ACTIVATION OF MICRODISK ELECTRODES EXAMINED BY FAST-SCAN RATE VOLTAMMETRY AND DIGITAL-SIMULATION

Fast-scan rate voltammetry in conjunction with background subtraction techniques has been used to examine the effect of laser activation at carbon fiber microdisk electrodes. The voltammetry observed after lase r treatment shows marked changes in electron transfer kinetics and in voltammetric symmetry. These voltammetric parameters are estimated by matching observed voltammetric behavior with digitally simulated volta mmograms. The composition and pH of the supporting electrolyte were fo und to play large roles in the observed voltammetry of catechols after laser activation of the electrode. Voltammetric symmetry of oxidation vs reduction waves is described by the apparent charge transfer coeff icient, beta. The asymmetry of fast-scan cyclic voltammograms of dopam ine, 4-methylcatechol, and 3,4-dihydroxyphenylacetic acid in a buffer system containing 0.05 M citrate and 0.05 M phosphate is presented; In this buffer system, beta is approximately 0.5 at pH 2.0 and significa ntly less than 0.5 at pH 6.0 and 7.0. interestingly, beta for dopamine electron transfer at pH 8.0 is above 0.5. Possible explanations for t he observed voltammetric asymmetry are presented in terms of electrost atic interactions and complexation of analyte molecules with anionic s olution species.