Abstract
This paper describes the pH dependence of cyclic voltammograms (CVs) of hexacyanoferrate(III) on microdisc gold electrodes (25 μm in diameter) modified with thioctic acid (TA) monolayers. The use of a microdisc electrode made it possible to directly compare the experimental CV data with theoretical simulation, and thus to discuss the main factors affecting voltammetric responses in ion-channel sensors (ICSs) based on electrostatic repulsion. Whereas unmodified gold microdisc electrodes gave very similar sigmoidal CVs at pH 2.5–7.5, TA-modified microdisc electrodes exhibited gradual decrease in the reduction current of from pH 2.5 to 5.5 due to the deprotonation of the terminal –COOH groups of TA monolayers. The experimental pH dependence was consistent with theoretical quasi-reversible steady-state voltammograms reflecting the Frumkin effect, suggesting that the changes in the electrode reaction kinetics affected by electrode surface charge would be one of the major factors that offer voltammetric response in such ICSs.
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