Covalent modification of a glassy carbon surface by electrochemical oxidation of r-aminobenzene sulfonic acid in aqueous solution

R-aminobenzene sulfonic acid (r-ABSA) was covalently modified on a glassy carbon electrode (GCE) by electrochemical oxidation in 0.1 M KCl aqueous solution. The presence of an r-ABSA monolayer on the GCE was proven by X-ray photoelectron spectroscopy (XPS). Electron transfer to Fe(CN)63− was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) on the modified electrodes in solutions of various pHs. Changes in the solution pH value result in the variation of the terminal group (sulfonic acid group) charge state, based on which its surface pKa values are estimated. The r-ABSA monolayer film on GCE has good stability and can be used as a charge-rich precursor to assemble oppositely charged species by layer-by-layer electrostatic interaction. For example, multilayer films of anionic Fe(III) tetrakis(p-sulfonatophenyl) porphyrin (FeTSPP) and cationic polymer diazo-resins (DAR) can be obtained on the r-ABSA/GCE based on electrostatic and covalently attached interaction and the resulting modified electrodes have good electrochemical response and stability.