Facilitated cation transfer at a three-phase junction and its applicability for ionophore evaluation

Abstract

Abstract Although many redox probes have been used for anion transfer studies in three-phase electrode setups, only a few molecules have been applied for cation transfer. In this work we show that the fullerene C60 is an efficient redox system for this application. We performed ionophore assisted ion-transfer studies in a droplet system, a disposable setup with a cylindrical electrode, as well as a novel paper-based device. The disposable setup is easy to assemble and thanks to the cylindrical electrode creates a more stable and reproducible phase boundary than the standard droplet setup. With this new setup we were able to measure both assisted and unassisted cation-transfer at the three-phase boundary. Additionally, the proposed system was applied to compare the performances of three popular potassium ionophores: Valinomycin, dibenzo-18-crown-6 ether (DB18C6) and Potassium Ionophore III (BME-44). Here, ionophores, normally applied in ion-selective electrodes (ISE), can be easily evaluated and compared without the influence of other components of the ISE membrane such as plasticizers or lipophilic salts. Three-phase ion-transfer voltammetry is a convenient mean to assess the effect of each ionophore on both the selectivity and Gibbs energy of transfer.