How to Analyze Ionic Liquid Anions? Investigation into the Application of Suppressed and Non-Suppressed Ion Chromatography

Abstract

In the present study, two reliable and accurate methods have been developed for the quantitative and qualitative determination of ionic liquid anions based on suppressed and non-suppressed ion chromatography. They were applied to the separation and analysis of chloride, bromide, p-tosylate, tetrafluoroborate, hexafluorophosphate, dicyanamide, and bis(trifluoromethanesulfonyl)imide. In the non-suppressed mode, the influence of the concentration of phthalic acid, acetonitrile, and pH of the mobile phase on the retention and separation of analytes were investigated; 8 mM solution of phthalic acid with 20% v/v of acetonitrile (pH = 4) can be regarded as the optimal mobile phase in this separation mode. In the suppressed mode, various compositions of a carbonate/bicarbonate buffer solution with and without acetonitrile were also assessed; 3.2 mM Na2CO3/1 mM NaHCO3 and 25% acetonitrile were found to act as the optimal mobile phase. Under the analytical conditions developed, both methods provided very good separation and symmetrical peak shapes of all compounds within the reasonable time-frame of 30 min. The analytical performance parameters of both methods were good; however sensitivity will be further improved in future studies. Moreover, the suppressed separation mode was successfully applied to the analysis of tetrafluoroborate in a soil aquifer.