Polar silica-based stationary phases. Part I - Singly and doubly layered sorbents consisting of TRIS-silica and chondroitin sulfate A-TRIS-silica for hydrophilic interaction liquid chromatography

Two polar silica bonded stationary phases were prepared by first functionalizing the silica surface with -glycidoxypropyltrimethoxysilane, which was then reacted with TRIS to yield a polyhydroxy surface that also has secondary amine functionalities. This step produced the singly layered TRIS-silica column, a cationic hydrophilic column. The TRIS-silica surface was further coated with a layer of chondroitin sulfate A (CSA) yielding the doubly layered hydrophilic CSA-TRIS-silica column. The adsorbed CSA layer provided enhanced hydrophilicity and multi-mode interactions with polar solutes leading to different retention behavior and selectivity compared to the singly layered TRIS-silica column. The anionic sulfate and carboxylate groups in the CSA coating are electrostatically attracted by the cationic TRIS-silica surface yielding a relatively stable physically anchored CSA layer under HILIC elution conditions. The CSA-TRIS-silica column exhibited dual cationic and anionic character with mobile phases at pH similar to 3.0 and pH > 4.5, respectively. When comparing solute retention observed on both columns under identical elution conditions, the k values of neutral and cationic solutes were significantly higher on the more hydrophilic doubly layered CSA-TRIS-silica column whereas anionic solutes showed lower k values due to the electrostatic repulsion from the CSA layer.