Responsive switchable deep eutectic solvents: A review

Deep eutectic solvents (DESs) have drawn considerable attention as a new type of green solvent since they were reported. Subsequent studies have shown that DESs have the potential to be used as “designable” solvents, which means that the precursors of DESs with different structures and properties can be screened to customize DESs for specific functions. Researchers have found that during the sample preparation process involving DESs, the specific properties of some “smart” DESs can be switched by directing external driving forces, leading to a reversible phase transition of the target solution. These "smart" DESs are called switchable deep eutectic solvents (SDESs). The advent of SDES simplifies the sample pretreatment steps, reduces the use of organic solvents, and makes solvents easy to recycle, which matches the concept of green and sustainable chemistry. Compared with the number of previous experimental studies, the reviews and summaries on SDESs are rare. Therefore, this review made a summary of the concept and research progress of SDESs based on some related works in the past decade, including composition and type, characterization, switching mechanism, etc. It is expected to provide a certain reference and guidance for the subsequent in-depth research of SDESs in the analytical sample pretreatment.