FAST PULSED AMPEROMETRIC DETECTION AT NOBLE-METAL ELECTRODES - A STUDY OF OXIDE FORMATION AND DISSOLUTION KINETICS AT GOLD IN 0.1 M NAOH

The anodic charge (q(a)) for oxide formation, obtained by potential-step chronocoulometry at a Au mini-disk electrode, is nearly a linear function of log (t/ms) for t = ca. 3-30 ms with a slope proportional to the applied overpotential for oxide formation. It was demonstrated that, contrary to popular opinion based on voltammetric observation at slow scan rates (phi), the anodic current for oxide formation obtained using a linear potential-scan waveform is not a linear function of phi at large values of phi . It was also demonstrated that a reverse potential-step waveform can be used to interrupt the rapid oxide growth and, perhaps, inhibit the conversion of the hydrous oxide (AuOH) to the inert oxide (AuO). This result has probable significance for decreasing the background current during anodic pulsed amperometric detection of amines and sulfur compounds whose oxidation mechanisms are believed catalyzed by AuOH but not by AuO. The cathodic charge (q(c)) for oxide dissolution is approximately a linear function of t with a slope that is proportional to the applied potential.