Polymerizable Zwitterionic Liquid Stationary Phases With Improved Thermal Stability for Separation of Carboxylic...

Polymerizable zwitterionic liquids (ZILs) were investigated for the development of thermally stable wall-coated open-tubular (WCOT) stationary phases for gas chromatography (GC) in the separation of volatile carboxylic acids (VCAs). Three imidazolium-based ZILs containing alkenyl and acrylate functional groups were synthesized and evaluated based on their polymerization and used as separation media. Among the evaluated chemical structures, only the acrylate ZIL demonstrated the ability to undergo free radical polymerization and was subsequently employed in the preparation of chromatographic columns. WCOT columns were prepared by the static coating method followed by in-situ polymerization inside the GC capillary columns, resulting in chromatographic efficiencies up to 3300 plates m^-1. The resulting stationary phase enabled separation of VCAs under isothermal conditions at 100°C and exhibited reduced bleed (from 6.92-7.80 pA at 40°C to 154.70-157.57 pA at 250°C) compared to a corresponding non-polymerizable ZIL (from 7.58 pA at 40°C to 396.38 pA at 250°C), indicating improved thermal stability of the stationary phase upon polymerization. However, thermal treatment up to 250°C resulted in no chromatographic retention of benzyl alcohol, suggesting that the stationary phase undergoes an increase in rigidity under these conditions. To address this limitation, poly(ethylene glycol) methacrylate (PEGMA) was incorporated as a co-monomer at 10%, 20%, 25%, and 40% weight fractions to introduce flexibility within the polymeric network. With increasing PEGMA content, progressively narrower peaks of benzyl alcohol were observed after thermal treatment (3.3, 1.10, 0.81, and 0.194 min for 10%, 20%, 25%, and 40% weight fractions, respectively), indicating improved mass transfer within the stationary phase. These results demonstrate the feasibility of polymerizable ZIL stationary phases for GC and provide insight into the role of polymer composition in controlling chromatographic performance after thermal treatment.