Preparation of bi‐layer‐polymer coated silica using atom transfer radical polymerization and its application as restricted access phase for HPLC separation of hydrophobic molecules in biological fluids

A novel restricted access material was prepared by surface initiated atom transfer radical polymerization. The bi-layer-polymer structures were created on the surface of silica layer-by-layer. The inner layer was composed of poly(styrene-co-divinylbenzene), which was grafted first for binding small molecules based on hydrophobic and π–π interactions. The poly(styrene-co-divinylbenzene) bonded silica has good selectivity for aromatic hydrocarbons. It also has hydrophobicity and column efficiency similar to a C18 bonded silica. The material has shown good ability of protein exclusion after grafting hydrophilic polymer on the external surface while its hydrophobicity and selectivity do not have obvious change. It demonstrated that the material is still qualified for hydrophobic extraction. In the study, the relations between the polymer structures and chromatographic properties of the materials were investigated. The synthetic conditions were optimized. The results have shown that the material prepared in the study has application potential in the HPLC analysis of hydrophobic molecules from biological samples by direct injection. It demonstrated that atom transfer radical polymerization can be used as a method in the preparation of restricted access material.