Imidozolium Ionic Liquids as Mobile Phase Additives in Reversed Phase Liquid Chromatography for the Analysis of Anions

An analytical method was developed for the simultaneous determination of bromide, thiosulfate, thiocyanate, hexafluorophosphate, trifluoroacetate and trifluoromethanesulfonate anions by reversed phase liquid chromatography with indirect ultraviolet detection using imidazolium ionic liquids as mobile phase additives. The effects of imidazolium ionic liquids, organic solvent, column temperature and detection wavelength on separation and detection of the anions were investigated and the mechanism was discussed, in which imidazolium ionic liquids acted as ion pair reagent and background ultraviolet absorption reagent of indirect ultraviolet detection. The suitable chromatographic conditions were methanol/0.5 mmol L-1 1-ethyl-3-methyl imidazolium tetrafluoroborate aqueous solution (10/90, v/v) as mobile phase, column temperature of 35 degrees C and flow rate of 1.0 mL min(-1). The results indicated that the successful separation of the six anions within 10 min was achieved and the symmetry of peaks was satisfactory. Under these conditions, the detection limits of anions ranged from 0.02 to 0.52 mg L-1. Relative standard deviations for peak area and retention time were less than 0.24 and 0.46%, respectively. The method was applied to the determination of ionic liquid samples synthesized by chemistry laboratory. The results were accurate and reliable, and could meet the requirements for quantitative analysis.