Homogeneous liquid-liquid microextraction based on deep eutectic solvents

Deep eutectic solvents (DESs) have attracted a lot of interest as a green alternative to ionic liquids and organic solvents in different fields. The DESs are defined as a mixture of two or more pure compounds for which the eutectic point temperature is below that of an ideal liquid mixture. The history, properties, and synthesis procedure of DESs are briefly described herein. The majority part of this paper is devoted to reviewing the homogenous liquid-liquid microextraction methods (HLLME) based on DESs. In this microextraction process, a homogeneous phase is formed by adding a small volume of a water-miscible solvent as the extraction phase to the aqueous donor phase. Phase separation can be motivated by a number of various driving factors. The HLLME methods are classified in this work based on the phase separation stimulating factors, including the addition of a hydrophobic solvent, pH adjustment, temperature adjustment, and other new strategies.