| An investigation of ion-pair chromatography was carried out to analyze ionic liquid ions which have UV absorption or no UV absorption. The purpose is to develop simple new methods to determine ionic liquid ions by ion-pair chromatography. This study mainly contains three parts:First, in this article, a method of ion-pair chromatography with ultraviolet detection was used in the analysis of p-toluenesulfonate ionic liquid anion. The analyte was separated with silica-based monolithic column and detected by ultraviolet detector. The effect of detection wavelength and the composition of mobile phase on the retention and separation of p-toluenesulfonate were investigated. The chromatographic conditions were optimized, and the retention rules were discussed. At 230 nm wavelength, when 0.4 mmol/L TBA–0.13 mmol/L citric acid–acetonitrile(85:15, v/v; p H 5) were used as mobile phase with column temperature of 40℃ and flow rate of 3.0 m L/min, a good results of determination could be acquired in 1.25 min, and other common inorganic anion(Cl￣) did not interfere with the determination. In the range of 0.7–100 mg/L, the correlation coefficient of linear regression equation was 0.9997. The detection limit(S/N = 3) was 0.2 mg/L. The relative standard deviation was below 1 %. The method has been applied to the analysis of p-toluenesulfonate ionic liquid samples, and the spiked recovery was 100 %. The method is simple and reliable.Second, a method of ion-pair chromatography with indirect ultraviolet detection was established for the simultaneous determination of ionic liquid anions of trifluoroacetate, trifluoromethanesulfonate and tetrafluoroborate. In this experiment, the silica-based monolithic column was used as the separation column. The factors which have effect on the retention and detection of three anions were disscussed. Under the conditions of 210 nm as detection wavelength, 4 m L/min as flow rate, 30 ℃ as column temperature, and 1.26 mmol/L citric acid–0.5 mmol/L TBA –acetonitrile(97:3, v/v; p H 6.0) as mobile phase, the anions were completely separated and the system peaks didn’t interfere with the determination. The detection limits of the anions(S/N=3) were 0.34–0.98 mg/L. The relative standard deviations of the retention times and peak areas obtained by determining samples five times continuously were below 1 %. The spiked recoveries of the anions were from 99.0 % to 102 %.This method has been successfully used to determine ionic liquids synthesized by chemistry laboratory, and the results were accurate and reliable.Finally, a method of ion-pair chromatography with indirect ultraviolet detection was established for the determination of piperidinium ionic liquid cation in the enviromental water. In this experiment, a strong cation exchange extraction column was used for sepration and enrichment. The target was eluted by methanol and NH4Cl(30:70, v/v; p H 4.7), the analyte then directly injected into the chromatography system. The final selection of the chromatographic conditions were: 0.5 mmol/L 4-aminophenol hydrochloride-0.01 mmol/L 1-heptanesulfonic acid sodium-methanol(95:5, v/v) as eluent, the column temperature was 30 ℃ and the flow rate was 1.0 m L/min, the detection wavelength was set at 210 nm. In the range of 0.21–100 mg/L, the correlation coefficient of linear regression equation was good. The detection limit(S/N = 3) was 0.5 mg/L. The range of relative standard deviation was 0.6 %–2.0 %. The spiked recovery of the cation was 97 %. The sample stability was good within 12 h. The method is praticable and simple. It can be used for the detection of piperidinium ionic liquid cation in environmental water samples. |
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