反相离子对色谱-直接电导检测法分析六氟磷酸根离子液体阴离子

建立了反相离子对色谱-直接电导检测六氟磷酸根(PF6-)离子液体阴离子的分析方法。用DiamonsilC18反相色谱柱为分离柱,以离子对试剂-柠檬酸-乙腈混合水溶液为流动相,考察了离子对试剂、乙腈含量、pH值及色谱柱温度对六氟磷酸根保留的影响,并讨论了相关保留机理。在优化的色谱条件下,即流动相为0.05 mmol/L氢氧化四丁铵-0.038 mmol/L柠檬酸-35%乙腈(pH 5.5),流速1.0 mL/min,色谱柱温度40℃时,PF6-与其它常见阴离子(F-、Cl-、Br-、NO3-、SO24-、BF4-)达到基线分离且保留时间在15 min内。方法检出限(S/N=3)为0.25 mg/L,标准曲线的线性范围为0.5～100.0 mg/L,峰面积和保留时间的相对标准偏差(n=5)分别为0.17%和0.15%。该法用于1-丁基-3-甲基咪唑六氟磷酸盐和1-丙基-2,3-二甲基咪唑六氟磷酸盐两种离子液体中PF6-的测定,加标回收率分别为99%和104%。该方法简单、准确、可靠,实用性好。

Determination of Hexafluorophosphate Ionic Liquid Anion by Reversed-phase Ion pair Chromatography Coupled with Direct Conductivity Detection

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.