Glutathione-functionalized covalent organic frameworks@silica as a hydrophilic-hydrophobic balanced mixed-mode stationary phase for highly efficient separation of compounds with a wide range of polarity

Background

Covalent organic frameworks (COFs) are a highly promising stationary phase for high-performance liquid chromatography (HPLC), but the separation of polar compounds is limited by their low hydrophilicity. Therefore, it is crucial to develop novel COFs-based stationary phases with balanced hydrophilicity-hydrophobicity for the efficient separation of different polar compounds.

Results

In this paper, glutathione (GSH)-functionalized COFs@silica microspheres (GSH-COFs@SiO₂) were synthesized via a two-step, post-synthesis modification strategy. The COFs particles was constructed onto silica surface by the covalent conjugation of 1,3,5-tris(4-aminophenyl)benzene and 2,5-divinylterephthalaldehyde. GSH containing abundant –NH₂ and –COOH groups was bonded onto the surface of COFs@SiO₂ to further enhance hydrophilicity. The resulting GSH-COFs@SiO₂ exhibited balanced hydrophilicity-hydrophobicity and can be used in hydrophilic/reversed-phase liquid chromatography modes through multiple retention mechanisms. Consequently, a variety of compounds with different polarity, including nucleosides/bases, benzoic acids, anilines, phenols, alkylbenzenes and polycyclic aromatic hydrocarbons, were well separated with ideal resolution, satisfactory column efficiency and good peak shapes. Furthermore, this novel column exhibited remarkable column stability, as evidenced by intra-day relative standard deviations of 0.08 %–0.18 % for retention time and 0.45 %–1.47 % for peak area.

Significance and novelty

This work demonstrates the superior hydrophilic-hydrophobic selectivity of GSH-COFs@SiO₂ stationary phases towards compounds with a wide range of polarity and provides a very facile and easily popularized post-synthetic modification route for hydrophilic-hydrophobic balanced COFs-based HPLC stationary phases.