RAPID METHOD FOR DETERMINATION OF HOMOLOGUE IMIDAZOLIUM IONIC LIQUID CATIONS BY ION-PAIR CHROMATOGRAPHY USING A MONOLITHIC COLUMN

A fast and gradient ion-pair chromatographic method was developed for determination of five homologue imidazolium ionic liquid cations using a silica-based monolithic column and ultraviolet detection. Chromatographic separations were performed on a Chromolith Speed ROD RP-18e column with 1-heptanesulfonic acid sodium aqueous solution (pH adjusted by citric acid)-acetonitrile as the mobile phase. The effects of chromatographic column, mobile phase, flow rate, and column temperature on retention and separation of the cations were investigated. The retention rules of homologue imidazolium cations were discussed. The results showed that the analysis time could be significantly reduced owing to the application of monolithic column. Simultaneous and fast separation of five imidazolium cations was achieved under the optimum chromatographic conditions. Detection limits (S/N=3) for the cations were 0.26-1.61mg/L. Relative standard deviations (n=5) for peak areas and retention times were less than 0.8%. The method has been successfully applied to the determination of two ionic liquids synthesized by chemistry lab. Recoveries of the cations after spiking were 96.8-101.9%.