Stimulus-responsive smart solvents and their application in analytical liquid-liquid (micro)extraction techniques

Switchable-hydrophilicity solvents are a new type of solvents that could be very promising for liquid-liquid (micro)extraction. Nevertheless, they have been scarcely used in this critical step of chemical analysis. This article presents a comprehensive and critical review of fundamentals, chemical factors and stimulus, that reversibly modify the polarity of these solvents. This unique characteristic allows the reversible transition of the solvent from a hydrophobic to a hydrophilic state, favoring liquid-liquid (micro)extraction. Special attention is paid to new types of stimuli as light and voltage to extend the applicability of these exciting solvents in liquid-liquid (micro)extraction. • Switchable-hydrophilicity solvents are promising candidates for analytical liquid-liquid (micro)extraction. • The chemical properties that regulate the changes in polarity of smart solvents are discussed. • Different stimuli used with switchable-hydrophilicity solvents are presented. • Applications of smart solvents in liquid-liquid (micro)extraction techniques are outlined. • Investigation of new stimuli will drive analytical liquid-liquid (micro)extraction forward.