Mutual solubility of hydrophobic ionic liquids and water in liquid-liquid two-phase systems for analytical chemistry.

Liquid-liquid two-phase systems formed by a hydrophobic ionic liquid and water find several useful ways of application in analytical chemistry. One of the most important properties of such two-phase systems is the mutual solubility of the IL and water. Recent advancements on this subject have been reviewed. The solubility of ionic liquids in water is related to the standard Gibbs energies of the transfer of ions constituting the ionic liquid from the ionic liquid phase to water. Although this single ionic property cannot be measured thermodynamically and also varies from one ionic liquid to another, the standard Gibbs energy of the ion transfer from a polar aprotic solvent, such as nitrobenzene and 1,2-dichloroethane, to water is a convenient measure for it. The solubility of an ionic liquid in water and the electrochemical properties at the interface between the two phases are intimately related with each other.