Ionic liquids in chromatographic and electrophoretic techniques: toward additional improvements in the separation of natural compounds

Abstract

Due to their unique properties, in recent years, ionic liquids (ILs) have been largely investigated in the field of analytical chemistry. Particularly during the last sixteen years, they have been successfully applied in the chromatographic and electrophoretic analysis of value-added compounds extracted from biomass. Considering the growing interest in the use of ILs in this field, this critical review provides a comprehensive overview on the improvements achieved using ILs as constituents of mobile or stationary phases in analytical techniques, namely in capillary electrophoresis and its different modes, in high performance liquid chromatography, and in gas chromatography, for the separation and analysis of natural compounds. The impact of the IL chemical structure and the influence of secondary parameters, such as the IL concentration, temperature, pH, voltage and analysis time (when applied), are also critically addressed regarding the achieved separation improvements. Major conclusions on the role of ILs in the separation mechanisms and the performance of these techniques in terms of efficiency, resolution and selectivity are provided. Based on a critical analysis of all published results, some target-oriented ILs are suggested. Finally, current drawbacks and future challenges in the field are highlighted. In particular, the design and use of more benign and effective ILs as well as the development of integrated (and thus more sustainable) extraction-separation processes using IL aqueous solutions are suggested within a green chemistry perspective.

Fundamental Properties of Packing Materials for Liquid Chromatography

“…The miscibility of ILs with water permits the reduction of organic solvent concentrations; therefore, analytical methods using IL can be called greener chemistry [49][50][51][52]. Different QSAR studies have been performed on ILs and highlighted their safety, health, and environmental issues [47].…”

“…Different QSAR studies have been performed on ILs and highlighted the safety, health, and environmental issues [49,50]. Extraction-separation processes using aqueous IL solutions have been suggested from a green chemistry perspective [51]. ILs are proposed for greener, faster, and simpler sample preparation [52].…”

Improved ionic-liquid-functionalized macroporous supports able to purify nucleic acids in one step

“…ILs are salts, usually described as liquid salts below 100 °C, which can be tailored in terms of their properties, such as polarity, density, viscosity, conductivity, among others [ 17 , 18 ]. ILs have been used in liquid chromatography in distinct ways [ 19 , 20 ]: as additives of mobile phases [ 21 ], as ligands of stationary phases [ 22 , 23 ], or acting themselves as stationary phases [ 24 ]. In most of these works, it was demonstrated the high performance of ILs achieved by the effective design of their chemical structures.…”

Natural deep eutectic solvents as the major mobile phase components in high-performance liquid chromatography—searching for alternatives to organic solvents

“…Different approaches used to reduce organic solvents have been the introduction of surfactants [21] or additives to the mobile phase [8]. Some of these additives have included ionic liquids (ILs) [22] and deep eutectic solvents (DES), most of which can be environmentally considered as Bgreen^solvents. However, it is still important to note that most separations reported in the literature still use at least 10% organic solvents such as ACN or methanol (MeOH) [8,23].…”