INVESTIGATION OF THE KINETICS OF ASSISTED POTASSIUM-ION TRANSFER BY DIBENZO-18-CROWN-6 AT THE MICRO-ITIES BY MEANS OF STEADY-STATE VOLTAMMETRY

Micropipettes, with internal tip diameters ranging from 1.2 to 38 mu m, were fabricated using borosilicate glass capillaries. These were then used to support a micro-interface between two immiscible electrolyte solutions (micro-ITIES). The assisted ion transfer of potassium from water to 1,2-dichloroethane by the neutral ionophore dibenzo-18-crown-6 was followed using both cyclic voltammetry and chronoamperometry. Supplementary investigations included variation of potassium ion and dibenzo-18-crown-6 concentration and an ac impedance study of the micropipette tip resistance. These investigations showed that the assisted ion transfer process is not limited by charge transfer, but only by diffusion of the participating species. The lower limit of the standard rate constant, k(o) for the charge-transfer step was estimated to be 3 cm s(-1).