Analytical Applications of Ionic Liquids in Chromatographic and Electrophoretic Separation Techniques

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The synthetic tunability of ionic liquids (ILs), their structural versatility, and the wide range of interest properties that can present (from water soluble to water insoluble, from low density to high density, etc.), together with their impressive solvation abilities for different organic compounds, make their use in chromatographic and electrophoretic separation techniques an obvious approach of enormous interest. In fact, the studies of ILs have covered a number of topics in chromatographic and electrophoretic methods, from basic studies of performance to the development of complete analytical methods. Thus, they have been used in high-performance liquid chromatography (HPLC) as modifiers of mobile phases, as additives of mobile phases to improve the separation of basic analytes, as novel HPLC stationary phases, and even as pseudo-stationary phases in HPLC when utilizing ionic liquid-based surfactants, in a mode of micellar liquid chromatography (MLC). They have also experienced applications in counter-current chromatography (CCC), in which all phases involved have a liquid nature, acting as mobile phases or as stationary phases. In gas chromatography (GC), ILs have experienced an important application for developing novel stationary phases, characterized by their ability to separate polar and nonpolar compounds simultaneously, which is a problem in conventional GC columns. Moreover, they have been employed in capillary electrophoresis (CE) as background electrolytes in capillary zone electrophoresis (CZE), as pseudo-stationary phases in micellar electrokinetic chromatography (MEKC) if using IL-based surfactants at concentrations ensuring micelle formation and also in on-line CE preconcentration techniques based on the use of IL-based surfactants micelles such as sweeping-MEKC or micelle to solvent stacking, among others.