Green preparation of composite hydrogel coated hydrophobic long-chain carboxylic acid-bonded silica microspheres for mixed-mode chromatography

Combining composite hydrogel with silica gel can endow hydrogel with new application possibilities. In this work, polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) were combined into a composite hydrogel, which was then wrapped on the surface of 1-undecenoic acid (UA) bonded silica microspheres. As a result, a novel PVP/PVA composite hydrogel-functionalized silica stationary phase (PVP/PVA@Sil-UA) was prepared by a green and facile method. Specifically, the thiol-ene click reaction was preferentially used to bond a hydrophobic long-chain carboxylic acid (UA) on the surface of thiolated silica gel in deep eutectic solvent, which was able to provide abundant hydrogen bonding sites for the further coating of PVP/PVA composite hydrogel. The hydrophobic long alkyl chain not only improved the separation selectivity, but also effectively alleviated the swelling of hydrogel. It was discovered that the prepared PVP/PVA@Sil-UA showed outstanding separation performance for a wide range of samples. The study of retention behavior proved that the PVP/PVA@Sil-UA was a mixed-mode chromatographic stationary phase, possessing hydrophilic and hydrophobic retention characteristics. In summary, an eco-friendly method was applied to realize the effective combination of composite hydrogel and SiO2 due to the fact that no harmful organic solvents were used in the preparation process, which provided a novel idea for the application of composite hydrogel in the field of chromatographic separation.