Determining the Gibbs energy of ion transfer across water-organic liquid interfaces with three-phase electrodes

Ions can be transferred between immiscible liquid phases across a common interface, with the help of a three-electrode potentiostat, when one phase is an organic droplet attached to a solid electrode and containing a redox probe. This novel approach has been used in studies to determine the Gibbs energy of anion and cation transfer, ranging from simple inorganic and organic ions to the ionic forms of drugs and small peptides. This method of studying ion transfer has the following advantages: (1) no base electrolytes are necessary in the organic phase; (2) the aqueous phase contains only the salt to be studied; (3) a three-electrode potentiostat is used; (4) organic solvents such as n-octanol and chiral liquids such as D- and L-2-octanol can be used; (5) the range of accessible Gibbs energies of transfer is wider than in the classic 4-electrode experiments; (6) the volume of the organic phase can be very small, for example, 1 microL or less; (7) the experiments can be performed routinely and fast. Herein, the basic 5 principle is outlined, as well as a summary of the results obtained to date, and a discussion on the theoretical treatments concerning the kinetic regime of the three-phase electrodes with immobilized droplets.