Determination of ionic liquid anions of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate by ion-pair chromatography with direct conductivity detection

Abstract

An ion-pair chromatographic method with direct conductivity detection was established on a reversed-phase silica-based column for the simultaneous determination of ionic liquid anions of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate. The analytes were separated using a mobile phase of ion pair reagent-malic acid-acetonitrile on the Diamonsil C18 column. The effects of mobile phase composition and column temperature on the retention of the anions were investigated. The optimized chromatographic conditions were as follows: 0.15 mmol/L tetrabutylammonium hydroxide-0.099 mmol/L malic acid-20% (v/v) acetonitrile aqueous solution (pH 6.5) as mobile phase, a column temperature of 25 degrees C. Under the optimal conditions, the baseline separation of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate was achieved without any interference by other ordinary anions (fluoride, chloride, bromide, nitrate, sulfate). The detection limits (S/N = 3) were 0.21, 0.07, 0.36 and 0.12 mg/L for trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate, respectively. The method has been applied to the determination of the four anions in ionic liquids. The spiked recoveries of the anions were from 95.0% to 104.6%. The results demonstrate that the convenience, rapidity, sensitivity and accuracy are fit for the requirements of quantitative analysis of trifluoroacetate, thiocyanate, tetrafluoroborate and trifluoromethanesulfonate in ionic liquids.