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

Abstract

Two polar silica bonded stationary phases were prepared by first functionalizing the silica surface with γ-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 ∼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.