Determination and quantification of cations in ionic liquids by capillary electrophoresis-mass spectrometry

In this study, a capillary electrophoresis (CE) method hyphenated to a high-resolution mass spectrometer is presented to detect the cations in ionic liquids (ILs) and their decomposition products. The investigated ILs were 1-methyl-1-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₃TFSI), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₄TFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM TFSI). With this method, it was possible to achieve baseline separation of the decomposition products from the main cations in short migration times. Because of the successful baseline separation, it was also possible to quantify the main cations in ILs, which were aged at room temperature and at 60°C. Additionally, the relative standard deviations (RSDs) for the concentrations of the main cations investigated by CE and ion chromatography (IC) were given to compare the both methods with each other. The concentrations were determined for the main cations aged at different temperatures. Finally, the limits of detection (LOD) and quantification (LOQ) were calculated for this method and compared to the IC results. The LODs and LOQs for CE method was in the range of 0.3-2.1mg/kg and for the IC method 34.9-455.2mg/kg. Therefore, more decomposition products of EMIM⁺ were determined by the CE method than by the IC method. In each investigated IL, more decomposition products of the cations were detected at 60°C compared to room temperature. The PYR₁₄⁺ concentration decreased by 4 % at 60°C, while PYR₁₃⁺ and EMIM⁺ decreased more than 10 % aged at 60°C in contrast to the sample which was aged at room temperature.