Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Joe P. Foley

Abstract

The chromatographic properties of polymer-coated Unisphere aluminas for reversed-phase liquid chromatography were evaluated and compared to those of Si-C$\sb{18}$ phases. A greater difference in solvent strength between acetonitrile and methanol was observed for the Unisphere columns. Approximately equal methylene selectivity was also obtained for both stationary phase types. Evaluation of polar group selectivity showed the absence of hydroxyl group participation in solute retention for the aluminas. In terms of kinetic properties, acceptable reduced plate heights were obtained for the Unisphere columns at optimum velocities. However, the van Deemter curves for the aluminas showed a more rapid loss in efficiency with increasing solvent velocity. The applicability of the Unisphere columns for rapid analysis was also evaluated, and although a smaller normalized pressure drop was observed for the aluminas, especially at elevated flow rates, the larger reduced plate heights obtained for the aluminas at practical flow rates resulted in poorer resolution for the Unisphere columns. Finally, an investigation of the column re-equilibration process after gradient elution indicated that employing both high flow rate and high temperature will result in faster column equilibration, and that longer equilibration times are necessary for gradients started with pure water. The slurry-packing process for Versal GH and Versal GL aluminas was also optimized for applications in normal-phase liquid chromatography. Due to their greater mechanical stability, the GH aluminas were determined to be more promising than the GL as HPLC adsorbents. Both Versal GH and GL provided retention and selectivities similar to that of Unisphere alumina, although the GL was found to be slightly less retentive. It was also concluded that the slurry-packing of the GL aluminas is problematic. At low pressures, the GL alumina particles cannot be consistently packed with good (adequate) efficiency. At the (higher) pressures necessary for efficient column packing, GL aluminas fracture, producing fines which result in column blockage. Although the GH materials can be packed satisfactorily in the downward-flow mode using a density-balanced slurry, the costly, somewhat tedious density-balanced approach will probably not be necessary if an upward-flow packing mode is employed.

Pages

324

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