A digital simulation study of steady-state voltammograms for the ion transfer across the liquid-liquid interface formed at the orifice of a micropipette

Digital simulation of cyclic voltammograms for the ion transfer across the micro liquid-liquid interface formed at the orifice of a glass micropipette shows that the electrochemically driven flow of ions from the inside of the micropipette to the infinitely large outer phase gives steady-state current-potential characteristics, when the shape of the tip is not cylindrical but truncated conical as usual micropipettes. Such steady-state behavior well explains experimentally observed voltammograms for ion transfer across the hydrophobic ionic liquid-water interface formed at the orifice of a micropipette with a small radius. Both the limiting current and the half-wave potential of the voltammogram vary with the angle of the inner wall of the micropipette with respect to the axis of rotational symmetry of the pipette, theta(1), and both reach the limits predicted by the radial diffusion of the ions to the inlaid disk, that is, theta(1) = 90 degrees in an asymptotic manner. The conditions for obtaining such steady-state voltammograms depend on the size of the interface and the scan rate of the applied voltage, aside from theta(1). (c) 2008 Elsevier B.V. All rights reserved.