The Influence of Imidazolium Ionic Liquids on the Chromatographic Behavior of Some Aromatic Acids under Reverse-Phase High-Performance Liquid Chromatography Conditions

Using reverse-phase high-performance liquid chromatography, some features of the chromatographic retention of polar aromatic acids (gallic, ferulic, benzoic, and salicylic) on hexadecylsilica gel from aqueous-acetonitrile eluents containing imidazolium ionic liquids (ILs) were studied. The following ILs were used: 1-butyl-3-methylimidazolium bromide [C 4 MIM][Br], 1-hexyl-3-methylimidazolium bromide [C 6 MIM][Br], 1-decyl-3-methylimidazolium bromide [C 10 MIM][Br], and 1-methyl-3-octylimidazolium bromide [MC 8 IM][Br]. The dependences of retention on the structure of imidazolium ILs and aromatic acids were studied. Based on the temperature dependences of the retention factor, the thermodynamic characteristics of the sorption process (standard enthalpy and entropy component) were calculated. The obtained thermodynamic characteristics of sorption were analyzed, and the influence of the structure of the IL and sorbate on their values was shown. The compensation relationships between the enthalpy and the entropy component of the sorption of the studied aromatic acids were analyzed.