Temperature-responsive ionic liquid hydrogel coating silica used for multi-mode chromatographic stationary phase.

The research direction of high-performance liquid chromatography (HPLC) has always focused on the efficient synthesis and precise regulation of stationary phases. Therefore, the creation of chromatographic stationary phases with multiple interactions (hydrophobic, hydrophilic, and ion-exchange interactions), is seen as a critical step in achieving multi-mode chromatographic separation. In this study, an ionic liquid hydrogel was modified onto the surface of bare silica to synthesize a novel stationary phase (Sil@V1NV2). When compared to a hydrophilic interactions-dominated hydrogel, the experimental results revealed that the ionic liquid hydrogel not only amplified the hydrophobic interactions but also introduced ion-exchange interactions. This endowed Sil@V1NV2 with the capability to separate analytes in multi-mode, including hydrophilic chromatography (HILIC), hydrophobic chromatography (RPLC), and ion-exchange chromatography (IEC). It was noteworthy that the retention factor (k) for both benzoic acid and 4-hydroxybenzoic acid didn't adhere to the Van't Hoff equation. Extensive research has revealed that Sil@V1NV2 exhibited temperature-responsive characteristics at elevated temperatures due to the contraction of alkyl chains. This not only provided a reference for further research on ionic liquid hydrogel but also significantly broadened the application range of chromatographic separation in multi-mode.