Preparation and characterization of a lignin modified electrode

Alkali lignin undergoes strong adsorption on polycrystalline gold electrodes. Subsequent oxidation in a sulfuric acid solution leads to a restructured redox-active polymer that shows features characteristic for surface confined species. Surface coverage of up to 4.40 x 10(-10) mol cm(-2) may be obtained depending on the adsorption time or lignin concentration in the adsorption solution. Using Laviron's approach the electron-transfer rate constant and the transfer coefficient were found to be 8.9 s(-1) and 0.35, respectively. The formal potential of the redox couple shifted negatively with pH at a rate of ca. 60 mV/pH unit, suggesting a 2 e/2 H+ reaction. The redox couple was also found to be a good mediator for electrochemical ascorbic acid oxidation in neutral phosphate buffer with ca. 250 mV reduction of the oxidation overpotential.