Supramolecular solvents in the extraction of organic compounds. A review

The increasing pressure to decrease organic solvent usage in laboratories is fostering the search for alternative solvents. The liquid-liquid phase separation of surfactants, induced by environmental conditions, viz. temperature, electrolytes, pH, etc., has been largely used in analytical extraction and concentration schemes. The surfactant-rich phase is a nano-structured liquid, recently named as supramolecular solvent, generated from the amphiphiles through a sequential self-assembly process occurring on two scales, molecular and nano. This review covers progress on both theoretical and practical aspects related to the use of supramolecular solvents in analytical extractions reported over the last decade. Advances allowing a better understanding of the mechanisms of solvent production and solvent structure are outlined. Emphasis is then placed on solvent composition and its consequences on extraction efficiency, concentration factors and suitability for solubilising analytes over a wide range of polarities. Recent developments in formats and strategies making supramolecular solvents compatible with chromatographic and electrophoretic techniques along with a variety of detection systems are discussed. Applications of supramolecular solvents to the extraction of organic compounds mainly in the biological, environmental and agrifood areas are critically reviewed and main future trends outlined.