Rapid Determination of Trifluoromethanesulfonate and p-Toluenesulfonate by Ion-Pair Chromatography Using a Reversed-Phase Silica-Based Monolithic Column: Application to the Analysis of Ionic Liquids

Abstract

A method of ion-pair chromatography was developed on a reversed-phase silica-based monolithic column for the fast and simultaneous determination of trifluoromethanesulfonate (CF3SO3−) and p-toluenesulfonate (C7H7SO3−). The analysis was performed using a mobile phase of tetrabutylammonium hydroxide + citric acid + acetonitrile on the Chromolith Speed ROD RP-18e column with direct conductivity detection. The effects of the eluent, column temperature and flow rate on the retention of the anions were investigated. The experimental phenomenon was discussed according to hydrophobic interaction and ion-exchange mechanism in the separation. The optimized chromatographic conditions were selected. The optimized eluent for the separation consisted of 0.2 mmol L−1 tetrabutylammonium hydroxide + 0.10 mmol L−1 citric acid + 9% acetonitrile (pH 5.5). The flow rate was set at 6.0 mL min−1. The column temperature was 25 °C. Under the optimal conditions, the better separation of CF3SO3− and C7H7SO3− was achieved without any interference by other anions (Cl−, Br−, I−, NO3−, SO42−, ClO3−, BF4− and PF6−). The detection limit (S/N = 3) was 0.28 and 0.71 mg L−1 for CF3SO3− and C7H7SO3−, respectively. The method has been applied to the determination of CF3SO3− and C7H7SO3− in ionic liquids. The spiked recoveries of CF3SO3− and C7H7SO3− were 101.1 and 100.2%, respectively.