| A reversed-phase ion-pair chromatographic method using direct conductivity detection was developed for the determination of hexafluorophosphate（PF-6） ionic liquid anion.Chromatographic separation was performed on a Diamonsil C18 reversed-phase column using ion-pair reagent-citric acid-acetonitrile as mobile phase.The effects of ion-pair reagent,volume fraction of acetonitrile,pH and column temperature on the retention factor and separation of PF-6 were investigated.The mechanism of retention in the separation was discussed.The optimized chromatographic conditions for the determination of PF-6 were using 0.05 mmol/L tetrabutylammonium hydroxide（TBAH）-0.038 mmol/L citric acid-35% acetonitrile（pH 5.5） as mobile phase,at a flow rate of 1.0 mL/min and a column temperature of 40 ℃.Under the optimal conditions,the retention time of PF-6 was less than 15 min and the baseline separation of PF-6 was achieved without any interference by other common anions（Cl-,NO-3,F-,Br-,SO2-4 and BF-4）.The detection limit（S/N=3） for PF-6 was 0.25 mg/L.The good linear relationship was obtained between chromatographic peak area and concentration of PF-6 in the range of 0.5-100.0 mg/L.The relative standard deviations （RSD,n=5） of chromatographic peak area and retention time were 0.17% and 0.15%,respectively.The proposed method was applied in the determination of PF-6 in ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-propyl-2,3- dimethylimidazolium hexafluorophosphate.The spiked recoveries of PF-6 were 99% and 104%,respectively.The good linearity and repeatability of the method could meet the requirements for the quantitative analysis of PF-6 in ionic liquids.The method is simple,accurate,reliable and practical. |