IONIC LIQUIDS IN REVERSED-PHASE HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY OF PHENOLIC ACIDS ON DIFFERENT STATIONARY PHASES

Phenolic acids belonging to weak acidic compounds were analyzed in the reversed phase system, modified with the addition of ionic liquids: 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIM PF6) and 1-butyl-3-methyl-imidazolium chloride (BMIM Cl) on three different columns: Zorbax Extend-C18, Zorbax SB-Phenyl, and Zorbax SB-CN in acidic conditions. The effect of the concentration, the type of different ionic liquids, and the type of organic solvent on the analytes retention were examined on chosen stationary phases. It was established that the biggest changes of the retention factor of undissociated analytes were associated with addition of ionic liquid having the asymmetric cation enlarged with hydrophobic substituents possessing chaotropic properties and neutral anions. The retention mechanism was analyzed on the basis of k vs. ionic liquid concentration in aqueous-organic mobile phase with a constant amount of phosphate buffer.