VOLTAMMETRIC BEHAVIOR OF SCREEN-PRINTED CARBON ELECTRODES, CHEMICALLY MODIFIED WITH SELECTED MEDIATORS, AND THEIR APPLICATION AS SENSORS FOR THE DETERMINATION OF REDUCED GLUTATHIONE

The evaluation of screen-printed carbon electrodes, chemically modified with selected ferrocene, phthalocyanine and hexacyanoferrate(III) derivative mediators for the determination of reduced glutathione (GSH), is described. Cyclic voltammetry was used to investigate the effect of pH on the electrochemical behaviour of these mediators incorporated in the disposable electrodes. Values of the electron-transfer coefficient (alpha-n(a)) were calculated for the oxidation of the mediators in phosphate buffer solution and solutions containing 0.48 mmol dm-3 GSH. Amperometry in stirred solutions was used to construct hydrodynamic voltammograms for each of the modified electrodes; these voltammograms were used to elucidate their steady-state behaviour. Both electrochemical techniques were used to calculate the reduction in overpotential for the oxidation of GSH; these calculations were performed for all of the chemically modified electrodes. Amperometry in stirred solutions was used as the technique for quantitative measurements, to determine the calibration response factors (mu-A mmol-1 dm3) and limits of detection for selected mediators towards GSH. The appropriate applied potentials were selected by reference to the hydrodynamic waves; a range of values were investigated to find the potential that gave the maximum sensitivity. The most promising mediators were cobalt phthalocyanine, iron phthalocyanine and ferrocenecarbaldehyde.