Simultaneous determination of hexafluorophosphate and other trace impurity anions in ionic liquids by ion chromatography

A method was developed for the simultaneous determination of hexafluorophosphate and other trace impurity anions in ionic liquids by ion chromatography (IC). The sample was diluted with 70% (v/v) acetonitrile, filtrated by 0.22 mu m nylon filter membrane, and then analyzed by IC. The analytical column was Dionex IonPac AS22 (250 mm x 4 mm), carbonate-acetonitrile (70:30, v/v) was used as the eluent at a flow rate of 1.0 mL/min. The detection was performed by a Dionex DS6 conductivity detector. The quantitive analysis of external standard calibration curves was used. The linear ranges of the method for F-, Cl-, Br- and PF6- were 0.5 similar to 50 mu g/L (r=0.9999), 10 similar to 200 mu g/L (r=0.9998), 10 similar to 200 mu g/L (r=0.9999) and 0.9 similar to 45 mg/L (r=0.9998), respectively. The average recoveries were 94.5% F-, Cl-, Br- and PF(6)(-)100.5% with the relative standard deviations of 0.63%similar to 1.03%. The detection limits (S/N = 3) were 0.5 mu g/L, 2.0 mu g/L, 5.0 mu g/L and 0.9 mg/L for F-, Cl-, Br- and PF6-, respectively. The method has been applied to determine hexafluorophosphate and other trace impurity anions in ionic liquids with satisfactory results.