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 SiO 2 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.