Varchenko V. Modified carbon paste electrodes for the voltammetric determination of electroactive indole compounds

The thesis concerns electrochemical properties of vinpocetine, ondansetron and tropisetron at plain carbon paste electrodes as well as methods for the modification of these electrodes to improve their characteristics. All substances studied have been found to irreversibly oxidize at high anodic potentials with a one-electron transfer. The effect of scan rate and pH on electrochemical properties of these substances has been revealed using cyclic voltammetry. The slope of lgI vs. lgν relationship being about 0.5 indicated a diffusion-controlled reaction. It was assumed that the oxidation occurred at the tertiary nitrogen atom in either vinpocetine or tropisetron. However, ondansetron more likely oxidized at the indole fragment. For differential pulse mode, parameters known to affect voltammograms, such as pulse amplitude, pulse time and sweep rate, were studied. Optimal values were chosen to acquire well-shaped voltammograms with relatively high peak currents but relatively small background currents. Effect of varying an accumulation potential and accumulation time on differential pulse voltammograms was also evaluated. All three substances were found to be able to accumulate at carbon paste electrodes.