Capillary column coated with geminal ionic liquids as stationary phases for gas chromatographic separation

Four geminal ionic liquids (GILs), namely, 1,4-bis(1,1′-butyl-3,3′-methylene- imidazolium)-benzene bis[(trifluoromethyl)sulfonyl]imide (BBMIB-NTf₂), 1,4- bis(1,1′-butyl-3,3′-methylene-imidazolium)-benzene tetrafluoroborate (BBMIB-BF₄), 1,4- bis(1,1′-butyl-3,3′-methylene-imidazolium)-benzene hexafluophosphate (BBMIB-PF₆), and 1,4-bis(1,1′-methyl-3,3′-methylene-imidazolium)-benzene bis[(trifluoromethyl) sulfonyl] imide (BMMIB-NTf₂), were synthesized. They were statically coated onto the inner walls of fused-silica capillary columns and used as stationary phases for gas chromatography. The evaluation of BBMIB-NTf₂, BBMIB-BF₄, BBMIB-PF₆, and BMMIB-NTf₂ as stationary phases is reported here for the first time. These new stationary phases exhibit efficiencies of at least 2.3 × 10³ plates per meter. Abraham solvation parameter model was used to evaluate the solvation characteristics. The system constants indicated that the dipolarity/polarizability and the hydrogen-bond basicity play a major role among five molecular interactions between stationary phases and solute molecules. A fundamental understanding into the solvation characteristics of these GILs can be used as a guide to choosing the appropriate geminal ionic liquids for specific applications in various fields. The chromatographic separation performance was evaluated by a Grob test mixture, n-alkanes, alcohols, and aromatic isomers. Furthermore, the thermal stability was tested. The present results demonstrate that these geminal ionic liquids stationary phases possess excellent chromatographic separation performance and good thermal stability (at least up to 270 °C) and may be applicable as gas chromatography stationary phases for more application.