| Abstract [eng] |
The objective of the present work was the evaluation and comparison of the separation of imidazolium ionic liquid (IL) cations by using different UPLC separation modes and detailed investigation of the chromatographic behaviour of imidazolium ILs in hydrophilic interaction (HILIC) and per-aqueous liquid chromatography (PALC). UPLC technique in RP, IP and HILIC separation modes is applicable for the separation of six imidazolium cations under optimized conditions. HILIC was shown to outperform other chromatographic techniques used for ILs separations in terms of analysis time, separation efficiency and resolution. In the HILIC mode ethylene bridged hybrid silica column provides a dual retention mechanism with opposite separation selectivity depending on the composition of the mobile phase. In acetonitrile-rich (≥60% ACN) mobile phases the retention of solutes increases with increasing ACN content and hydrophilicity of the solutes (HILIC mode). In contrast, in the water-rich mobile phases (≤30% ACN) the retention increases with water content in the mobile phase with an opposite order of elution. The adsorption and partitioning models applied for HILIC and PALC separation modes showed that retention behaviour of imidazolium ionic liquids cannot be accurately described as neither pure partitioning nor pure adsorption mechanism. In PALC mode the mechanism is likely to be a mixture of RP and ion-exchange interactions, whereas in HILIC separation mode partitioning and ion-exchange interactions are responsible for the retention of cationic solutes. Finally, the conditions for the separation of twelve imidazolium ionic liquids were optimized in HILIC and PALC modes. |
