Effects of substituted functional groups of cations on retention performance of ionic liquid stationary phases in gas chromatography

Abstract

Thirteen stationary phases comprising a polyvinyl imidazolium ionic liquid (IL) in which cations containing propyl, butyl, nonyl, ethyl-phenyl, or cyan methyl functional groups are paired with bis(trifluoromethanesulfonyl) imide ([NTf2]-), trifluoromethanesulfonate ([TFO]-), and hexafluorophosphate ([PF6]-) were synthesized and directly coated inside capillary fused silica tubing for use in gas chromatography. The relationship between the structure of the ILs and the McReynolds constant, thermal stability, and retention behavior of the test compound on the prepared fused silica columns was examined and discussed. The influence of the cationic substituents on retention performance of stationary phases was also studied. The variation in the retention index of the test compound with temperature was also investigated. The results indicated that the synthesized ILs have strong polarity, and that their retention performance is closely related to not only the properties of the cationic substituent but also the structure of the substituted groups and the anion. In the temperature range investigated, the variation in the retention index of the tested compounds was the same as that of conventional chromatographic stationary phases.