ELECTROCHEMICAL-BEHAVIOR OF GLASSY-CARBON ELECTRODES MODIFIED BY ELECTROCHEMICAL OXIDATION

Glassy carbon electrodes were modified electrochemically by pretreatment in sulfate, phosphate or carbonate solutions by means of cycling the potential well into the positive limit of the solvent. Electrodes treated in this manner were then used to incorporate and concentrate a variety of redox species that were either cations or aromatic containing compounds, including Ru(bpy)3(2+), Ru(NH3)6(3+), Cu(NH3)4(2+), ferrocene, methylviologen, 1,4-benzoquinone, anthraquinone-2-sulfonate, riboflavin, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Surface-equivalent concentrations ranged from 5 x 10(-9) to 1 x 10(-7) mol cm-2 for electrodes pretreated for 10 min in sulfuric acid. An E1/2 vs. pH study of 1,4-benzoquinone, riboflavin, FMN and FAD in modified electrodes shows that the pK(a) values shift toward higher pH (nearly 2 pH units). Results concerning the incorporation of redox compounds detected only by mediation with other electroactive complexes and the study of the modified electrodes in electrocatalysis are also discussed.