Determination of Imidazolium Ionic Liquid Cations by Ion-Pair Chromatography Using a Monolithic Column and Direct Conductivity Detection

Determination of four imidazolium ionic liquid cations by ion-pair chromatography was carried out using direct conductivity detection. Chromatographic separations were performed on a silica-based monolithic column with 1-heptanesulfonic acid sodium + acetonitrile + citric acid as eluent. Carbon number rule and influence of acetonitrile on the retention of imidazolium cations were discussed. Detection limits (S/N = 3) for the cations were 2.1–55.9 mg L^?1. Relative standard deviations (RSD, n = 5) for peak areas were less than 3.0%. The method has been successfully applied to the determination of two ionic liquids synthesized by organic chemistry lab.