Engineered poly (ionic liquid) hydrogel with tunable alkyl chains for multi-mode stationary phases

Analysis of complex samples by high-performance liquid chromatography (HPLC) demands multi-mode stationary phases integrating hydrophilic, hydrophobic, and ionic interactions. Poly (ionic liquid) (PIL) hydrogel offers a designable platform for this purpose, but balancing their inherent hydrophilicity with sufficient reversed-phase retention remains challenging. We propose an "alkyl chain engineering" strategy to precisely tune the hydrophobicity of PIL hydrogel, aiming to achieve an optimal balance for multi-mode chromatography.

A series of PIL hydrogel stationary phases were synthesized by copolymerizing ionic liquids derived from tripentylamine (TPA, C5 long chain) and tripropylamine (TPrA, C3 short chain) on silica. The resulting Sil@TPA/TPrA-PIL hydrogel, with finely tuned hydrophobicity via alkyl chain engineering, exhibited improved peak shapes and broader separation ranges compared to both single-chain counterparts (Sil@TPA-PIL hydrogel and Sil@TPrA-PIL hydrogel). It successfully achieved multi-mode separations, including hydrophilic chromatography (HILIC), reversed-phase chromatography (RPLC), and ion-exchange chromatography (IEC).

This work provides a high-performance multi-mode stationary phase for complex sample analysis. More importantly, it establishes "alkyl chain engineering" as a rational and effective molecular design strategy for fabricating next-generation stationary phases with customizable hydrophobicity, offering a clear blueprint for advancing functional separation materials.