Advance of room temperature ionic liquid as solvent for extraction and separation

Room temperature ionic liquid is currently used to describe a broad class of low-melting semi-organic salts or salt mixtures which have appreciable liquid range. Composed entirely of ions, they are phenomenological analogs of classical metallic molten salts such as sodium chloride. Although an arbitrary divide, there is considerable consensus that such salts must melt at or below 100 degrees C to qualify as ionic liquid. In reality, hundreds of ionic liquids that are molten at or below room temperature have been reported and one that remains down to -96 degrees C is known. As ionic liquids have no detectable vapor pressure, this property avoids environmental and safety problems due to volatilization, as is the case in traditional organic solvents, ionic liquids are proposed as novel solvent systems to replace traditional solvents for extraction and separation. In the last five years, various ionic liquids have been widely used as a novel medium for the extraction and separation of metal ions, organic and biological compounds. Commonly, the extractions in ionic liquid/aqueous two phase system indicated a good selectivity and extraction efficiency, that excelled most with organic solvents. These extractions and separations combined with different analytical technologies have been widely applied to determine ultra trace metal ions and decrease the detection limit of corresponding classical analytical method remarkably. The following is a brief introduction and short review on these room temperature ionic liquids concerning their structures, solvent characteristics, extraction mechanism and application in analytical chemistry or other aspects.