Abstract:
Silica-based stationary phases are the foundation of high-performance liquid chromatography, yet their performance is limited by incomplete functionalization of surface silanols and the hydrolytic sensitivity of both the support and bonded ligands. These weaknesses result in unfavorable secondary interactions, column bleeding, and shortened column lifetimes, emphasizing the need for materials that combine enhanced stability with improved efficiency and novel selectivity. To address these issues, rational surface designs were developed and applied to stationary phase synthesis in this work. Silanization using silatranes was established as an innovative strategy, resulting in stable and efficient stationary phases. Their cage-like structure suppresses oligomer formation, enabling the creation of dense and uniform monolayers on the silica surface with a high fraction of trifunctional Si-O-Si bonds. The resulting thin films exhibit superior mass transfer performance and improved hydrolytic resistance. In parallel, polymer-based approaches provided an independent strategy for generating highly stable materials, albeit with some reduction in efficiency due to increased film thickness. The multipoint anchoring of polythiols via thermal or photo-induced click reactions on vinyl silica produced polymeric, thiol-rich coatings with excellent hydrolytic resistance, offering a versatile platform for further modification by classical thiol-ene chemistry or oxidation to tune selectivity. Crosslinking acted as a reinforcing principle to further increase hydrolytic stability. On silatrane-derived amino phases, crosslinking via epoxy-amine reactions generated highly crosslinked surface networks that improved stability without compromising selectivity or efficiency. On phenyl-modified silica surfaces, the use of thiol-yne chemistry instead of classical thiol-ene reactions produced doubly tethered ligands, strengthening their attachment to thiol-functionalized supports. Beyond stability and efficiency, new selectivity principles were explored. Tailored surface chemistries enabled applications in reversed-phase chromatography, hydrophilic interaction chromatography, ion-exchange, chiral, and mixed-mode chromatography. Particular emphasis was placed on controlling surface charge of the stationary phases. Through a fragment-based analysis of silica modified with zwitterionic chiral ligands, the respective contributions of ligand structure and the silica support to retention and surface charge were clarified. This knowledge guided the development of stationary phases with distinct charge characteristics. A phase with pH-dependent charge reversal was developed, enabling hydrophobic charge-induction chromatography of proteins under mild conditions. In addition, a set of triphenyl-modified stationary phases with differing surface charge properties was designed for biomolecule analysis. By integrating silatrane chemistry, thiol-rich polymeric platforms, crosslinking strategies, charged surfaces and pH-responsive functionalities, stationary phases were created that provide chemical stability, robustness, efficiency, and refined selectivity. These developments address long-standing limitations of silica-based stationary phases and significantly expand the toolbox for preparing chromatographic materials for pharmaceutical and bioanalytical applications in high-performance liquid chromatography.
Stationary Phase