Analysis of Facilitated Ion Transfer across Liquid-Liquid Interfaces Using Collision Electrochemisty

Abstract An electrochemical method was developed to analyze the alkali metal ion transfer across the water/1,2-dichloroethane interfaces facilitated by dibenzo-18-crown-6 ether (DB18C6) by observing the collisions of single emulsion droplets on an ultramicroelectrode (UME). The water-in-oil emulsion droplets were stabilized by an ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides, in which a highly hydrophilic redox probe of potassium ferrocyanide/ferricyanide (K3Fe(CN)6/ K4Fe(CN)6) was used. When the droplets collided with the UME that was biased at a potential to drive the oxidation reaction of [Fe(CN)6]4− (0.05 mol/L), the current spikes could be observed only with the addition of DB18C6. It was suggested that the DB18C6 as K+ ionophore facilitated the K+ transfer from the water to the oil to maintain charge balance during the electrolysis. As more K+ ionophores were added, the integrated charge of the current spikes showed a rising trend in general because of the ionophore to lower the Gibbs energy of ion transfer. Further collision experiments were conducted to investigate the transfer of Na+ and K+ cations facilitated by the DB18C6. The order in which the “voltammetric” oxidation waves appeared indicated that the ionophore of DB18C6 was more efficient in carrying K+ across the water/1,2-Dichloroethane interface. Thereby, the collision electrochemistry is a convenient and effective mean to study the ion selectivity of ionophore.