Ionic liquid-functionalized pillar[6]arene: A novel stationary phase of high selectivity towards a wide range of isomers

In this work, a novel pillar[6]arene bonded with octyl-imidazolium ionic liquids (IMP6A-C4) as a stationary phase for gas chromatographic (GC) separations was designed, synthesized, and characterized. The IMP6A-C4 capillary column, prepared by the static coating method, had medium polarity (133) and relatively high column efficiency of 4982 plates/m determined by n-dodecane at 120 ℃. As demonstrated, through the separation of the mixture of 17 aliphatic analytes and the mixture of 20 analytes with different polarities, the IMP6A-C4 column exhibited privileged retention and high resolving capacity for H-bonded and aromatic analytes, suggesting advantages over the P6A-C4 column and common polysiloxane HP-5 and HP-35 columns. Strikingly, it implemented high resolutions with good peak shapes for isomer mixtures of phenols, anilines, and benzaldehydes. These findings demonstrated that the excellent resolving performance of the IMP6A-C4 column can be attributed to the comprehensive interactions of its rigid 3D aromatic cavities and polar imidazolium ionic liquids, including π-π, ion-π, H-bonding, dipole–dipole interactions. On the other hand, the IMP6A-C4 capillary column exhibited good repeatability and reproducibility with the RSD% values in the range of 0.01–0.03% for run-to-run, 0.09–0.32% for day-to-day, and 2.72–5.23% for column-to-column. The satisfactory separation performance reveals the promising prospects of the IMP6A-C4 stationary phase in separation science.