Monomer-mediated fabrication of microporous organic network@silica microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography

Microporous organic networks (MONs) are promising in high performance liquid chromatography (HPLC) with large specific surface area, good hydrophobicity and stability. However, their superhydrophobic structures restrict MONs-based HPLC only in reversed-phase mode. To decrease the hydrophobicity of pristine MONs and to expand their broad application in HPLC, here we described the monomer-mediated fabrication of core-shell MON-2COOH@SiO2 microspheres for reversed-phase liquid chromatography (RPLC)/hydrophilic interaction liquid chromatography (HILIC) mixed-mode chromatography for the first time. The –COOH groups were introduced into MONs' skeleton to improve their hydrophilicity and to provide hydrophilic interaction sites. The MON-2COOH was grafted onto silica via a monomer mediated method to produce monodispersed core-shell microspheres. By adjusting the concentration of reactants, the thickness of MON-2COOH shell was easily manipulated. The packed MON-2COOH@SiO2 column showed high resolution and selectivity for separating both hydrophobic (alkylbenzenes, polycyclic aromatic hydrocarbons, anilines and phenols) and hydrophilic (nucleoside and nucleic bases) probes, highlighting the promise of MONs in mixed-mode HPLC. The MON-2COOH@SiO2 column also achieved good separation to sulfonamides, nonsteroidal anti-inflammatory drugs, flavonoids and phenylurea herbicides, and offered better resolution than commercial C18 and pristine SiO2 column. Multiple retention mechanisms were also found on MON-2COOH@SiO2 packed column, underlining the great potential of MONs in mixed-mode HPLC.