Monolithic Column Ion-Pair Chromatography with Indirect Ultraviolet Detection for the Determination of Three Acid Radical Anions Containing Fluorine in Ionic Liquids

A rapid ion-pair chromatographic method was developed on a monolithic column for the determination of trifluoroacetate, trifluoromethanesulfonate, and tetrafluoroborate. The three anions were successfully detected using indirect ultraviolet detection. These analyte anions were separated using a tetrabutylammonium hydroxide - p-toluenesulfonic acid – acetonitrile mobile phase on a silica-based monolithic column with an octadecyl functional group. The effects of detection wavelength, mobile phase, column temperature and flow rate on the retention of the anions were investigated. The chromatographic conditions were optimized and the retention properties were evaluated. Under the selected optimal conditions, the successful separation of the anions was achieved within 3.5 min. The detection limits were less than 1.0 mg/L for trifluoroacetate, trifluoromethanesulfonate, and tetrafluoroborate. The relative standard deviations for five repeated measurement of retention time and peak area were no more than 0.2%. The linear ranges extended across two orders of magnitude. The three anions in synthetic ionic liquid samples were successfully separated and detected by this method. The results show that the recoveries of this method were between 94.0% and 99.0%. The method was rapid, simple, and easy to use.