The development of new stationary phases have always been of great interest in HPLC and has become increasingly important in recent years mainly driven by rapidly evolving industrial need as well as the quest for higher throughput HPLC analyses for better resolution and higher sensitivity. In this thesis, we developed a family of silica based RPLC stationary phases based on a novel hyper-crosslinked (HC) platform, prepared through a multi-layer, two-dimensional, orthogonal polymerization reaction. The resulting stationary phases showed better stability, higher efficiency and novel selectivities, which are the three essentials properties of the stationary phase that users are looking for and column developers strive to achieve.
We first studied the synthesis and full characterization of a novel mixed-mode reversed-phase/weak cation exchange (RP/WCE) phase by introducing a small amount of carboxylate functionality into a hydrophobic hyper-crosslinked (HC) platform. The phase thus prepared shows a mixed-mode retention mechanism, allowing for both neutral organic compounds and charged bases to be separated simultaneously on the same phase under the same conditions. More importantly, the inherent weak cation exchange groups allow simple mobile phases to be used thereby avoiding the mass spectrometric ionization suppression problems concomitant to the use of non-volatile additives such as strong amine modifiers (e.g. triethylamine) to elute basic solutes from the strong cation exchange phases or ion pairing reagents (e.g. trifluoroacetic acid, ClO4-) to retain these solutes on conventional ODS phases. We next studied the development of a highly hydrophilic HC-OH phase prepared by hydrolyzing residual benzyl chloride groups on the hydrophobic platform. This phase is potentially useful as a candidate for use as the first dimension phase of comprehensive two-dimensional LC where column stability and low retentivity are greatly desired. We also developed a novel graphical method, the phase selectivity triangle plots, for visualizing the effect of surface chemistry (e.g. C18 vs. Phenyl vs. Fluoro) on stationary phase selectivities. The use of the new plots assists the selection of appropriate stationary phases for method development in both isocratic and gradient elution.
University of Minnesota Ph.D. dissertation. January 2010. Major: Chemistry. Advisors: Professor Peter W. Carr, Professor Philippe Buhlmann. 1 computer file (PDF); xviii, 231 pages.
Chromatographic selectivity and hyper-crosslinked liquid chromatography stationary phases..
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