Retention mechanism of selected ionic liquids on a pentafluorophenylpropyl polar phase: investigation using RP-HPLC.

This study investigated the retention mechanism of a congeneric group of imidazolium ionic liquid cations with alkyl functional groups of different lengths, an aryl substituent, and one pyridinium cation on a pentafluorophenylpropyl silica-based stationary phase. The influence of organic modifier type and content in the mobile phase on the retention mode of alkylimidazolium ionic liquid cations shows a 'U-shaped' relationship. The use of this stationary phase gives excellent linearity and detection limits in the ppt range. The method is also readily applicable to the highly selective analysis of plant extracts previously spiked with ionic liquids.