A novel urea-functionalized surface-confined octadecylimidazolium ionic liquid silica stationary phase for reversed-phase liquid chromatography

• A new urea-functionalized octadecylimidazolium stationary phase was synthesized.
• Superior aromatic selectivity over conventional C18.
• High affinity for polar-substituted aromatics.
• Enhanced hydrogen-bonding capacity and π–π stacking was observed.
• The urea group facilitated the retention and selectivity considerably.

One-pot synthesis of surface-confined ionic liquid functionalized silica spheres was proposed using N-(3-aminopropyl)imidazole, γ-isopropyltriethoxysilane and 1-bromooctadecane as starting materials. The surface modification of the silica spheres was successful with a high surface density of octadecylimidazolium, enabling the utilization of this new urea-functionalized ionic liquid-grafted silica material as stationary phase for high-performance liquid chromatography in reversed-phase mode. The long aliphatic chain combined with the multiple polar group embedded in the ligands imparted the new stationary phase fine selectivity towards PAH isomers and polar aromatics and higher affinity for phenolic compounds. The unique features of the new material, especially the effect of the urea group on the retention were elucidated by mathematic modeling.