New generation extraction solvents: From ionic liquids and aqueous biphasic systems to deep eutectic solvents

The review is devoted to extraction solvents of new generation, so called combined solvents, which include ionic liquids, aqueous biphasic systems and eutectic solvents. Most of modern combined solvents are based on organic ionic components. These solvents are associated with high expectations as they are able to provide the environmental safety and green character of extraction, which are priority tasks for the development of chemistry and chemical engineering. For all classes, an overview and a brief history of research are presented; details of structure and properties are discussed; various extraction systems are compared; and typical examples of extraction of metal ions and organic compounds are given. The lack of uniform terminology and difficulties in interpreting the behaviour of some systems, especially eutectic solvents, are outlined. The advantages and drawbacks of new generation extraction solvents and relevant research tasks are summarized. The bibliography includes 408 references.