The Liquid-Junction Potential at the Contact of Two Immiscible Electrolyte Solutions in the Absence of Supporting Electrolytes Reference Electrodes Reversible to Alkylammonium Ions and Tetraphenylborate Ion in Nitrobenzene

The liquid-junction potentials between two immiscible electrolyte solutions have been studied for the interface: R1+TPB−(nitrobenzene)/R1+X−(water) and R1+TPB− (nitrobenzene)/Li+TPB−(water), where R1+ is a tetraalkylammonium ion, TPB− is tetraphenylborate ion, and X− is a halide ion. These interfaces may be seen as a simplest form of either a liquid ion-exchange membrane ion-selective electrode sensing the activity of the ion in the aqueous phase or a reference electrode of a liquid membrane type reversible to the ion in the nonaqueous phase. The effects of the cationic species(R1+), the anionic species(X−) and the concentration of the electrolytes on the electrical potential difference developed at the interface have been studied. These properties of the interfaces were compared with a simplified theoretical treatment of the liquid-junction potential between the two immiscible solutions. The theory can predict the basic features of the system by knowing the standard ion-transfer potentials and the diffusion coefficients of the relevant ions as well as its concentration. In the concentration range where a significant deviation from the Nernstian response of the liquid-junction potential occurred, the diffusion potential has been demonstrated to contribute significantly to the liquid-junction potential.