MOF-74@SiO₂ core-shell stationary phase: Preparation and its applications for mixed-mode chromatographic separation

The development of versatile mixed-mode stationary phase materials is of important meanings for solving the increasing demands for real sample analysis. Herein, with 2,5-dihydroxyterephthalic acid as the organic ligand and nickel as the metal centre, MOF-74 nanocrystal materials were facilely grafted on the surface of carboxyl-functionalized silica gel via layer-by-layer assembling technique. The structures of the monodisperse MOF-74@SiO₂ material were proved by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, elemental analysis, thermogravimetric analysis, and Brunauer-Emmett-Teller specific surface area and pore size analyzer, respectively. Because the introduced 2,5-dihydroxyterephthalic acid is of hydrophilic carboxyl and hydroxyl groups, the packed MOF-74@SiO₂ column reveals hydrophilic interaction/reversed-phase mixed-mode retention properties. Compared with commercial C₈ column or silica-based column, the MOF-74@SiO₂ column shows distrinct separation selectivity in short separation time for polycyclic aromatic hydrocarbons, phenolic compounds and polar sulfonamide compounds. The developed MOF-74@SiO₂ column was further successfully applied for the separation and detection of illegal addition of glucocorticoid in children's face cream as well as sulfonamides veterinary drug residues in pure milk. The research provides a simple and convenient approach to prepare multifunctional MOFs-based stationary phase materials.