Ionic Liquid-Based IPRs

Ionic liquids (ILs) have been recognized since the early 1900s. They are molten salts with low melting points, usually below 100°C. They were introduced in organic synthesis as a new class of polar, non-molecular solvents in the late 1990s and have recently attracted interest in a variety of fields since solvents are at the heart of most chemical processes and ionic liquids show an exclusive and fascinating wide range of physico-chemical properties. 

High thermal stability, negligible vapor pressure, low flammability, good conductivity, wide electrochemical windows, liquid ranges of several hundred of degrees liquid, 

Separation science focuses on room temperature ionic liquids (RTlLs), salts that are liquid at ambient temperature. They have been studied as extracting solvents, stationary and mobile phases, mobile phase additives, and other uses. Common RTILs consist of a bulky nitrogen- or phosphorus-containing organic cation (pyridinium or pyrrolidinium, alkyl-imidazolium, ammonium or phosphonium) and a variety of organic and inorganic anions (triflate, dicyanamide, trifluoroacetate, acetate trifluo-romethylsulfate, nitrate, perchlorate, bromide, chloride, chloroaluminate, tetrafluo-roborate, hexafluorophosphate). 

In liquid chromatography and electrophoretic methods, ILs are mostly used in diluted form in aqueous solutions. If its concentration is lowered to the millimolar range, an IL may be used as a mobile phase ionic additive. Their breakthrough for use in RP-HPLC was due to their ability to suppress deleterious effects of silanophilic interactions that represent the main drawback of silica-based stationary phases they also exhibit many other favorable physical attributes [116]. 

The IPC theory [10] gives a clear and easy rationalization of analyte retention dependence on the presence of ILs used as additives in the mobile phase in low concentrations. In this case, their specific properties as non-molecular polar solvents are not important. In fact, they are salts characterized by a dual nature because of the different properties of the cation and anion. Both contribute to solute retention and 

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