Detection of zwitterion at an electrified liquid-liquid interface: A chemical equilibrium perspective

Ion transfer across the Interface between Two Immiscible Electrolyte Solutions (ITIES) has been successfully used for chemical sensing and the determination of the equilibrium constants of ion complexation reactions. Recently, we reported the detection of a zwitterion, gamma-aminobutyric acid (GABA), at nanoITIES where an organic acid was added into the oil phase as a pH modulator to enable the detection of the zwitterion [1]. Accompanying our first introduction of an organic acid to the oil phase of ITIES, apart from ion complexation equilibrium associated with the assisted ion transfer, additional equilibria are formed including acid-base and partition equilibria. Here, we studied the chemical equilibrium reactions involved in this system, where we measured the unknown equilibrium constants using conventional separation and electrochemical methods. We further demonstrated that how concentration of ionophore in the oil phase impacts the electrochemical reaction, which can be explained by Le Chatelier's principle.