Study of retention mechanism of imidazolium-based ionic liquids in HPLC.

Retention mechanism of ionic compounds is still not fully known and investigated. It concerns especially ionic liquids (ILs) and HPLC. In the present study, interactions between imidazolium ILs and stationary phases were investigated in complex manner. For that purpose, five ILs, eight packing materials (with different functional groups bonded to silica surface) and three different pH of mobile phases were chosen. A great variety of applied chromatographic columns, as well as the changes made in mobile phase, allows for the description of retention mechanism. The main interactions responsible for retention process appear to be electrostatic, pi-pi and hydrophobic. Such complex results are presented for the first time.