Hydrophobic deep eutectic solvents for the extraction of organic and inorganic analytes from aqueous environments

New-generation solvents termed deep eutectic solvents (DESs) are attracting increasing attention as eco-friendly solvents in analytical chemistry. Recently, a new subclass of DESs called hydrophobic DESs (hDESs) has been reported. hDESs are generally immiscible with water and have high extraction efficiency for nonpolar analytes; thus, they have been suggested as potential extraction media to replace toxic organic solvents or expensive hydrophobic ionic liquids. Since the first introduction of hDESs in 2015, a growing number of studies on the application of hDESs in sample preparation methods have been reported. The present review provides an overview on the preparation and physicochemical properties of hDESs, followed by applications of hDESs in the extraction of organic and inorganic analytes from aqueous environments. In this review, up-to-date studies of conventional (liquid–liquid extraction) and miniaturized (liquid-phase microextraction) scale processes will be discussed with a focus on work up to January 2019.