PHYSICAL AND CHEMICAL CHARACTERIZATION OF TAILORED CHROMATOGRAPHIC ADSORBENTS

Abstract

The reaction between nitrogen-containing organic compounds (pyridines and amines) and alumina was studied through the use of chromatographic titrations and elemental analysis. The aluminum-nitrogen bond was the basis for the preparation of a series of new chromatographic adsorbents. A series of amines and pyridine homologs were bound to alumina and evaluated as chromatographic stationary phases. The surface coverage was determined using elemental analysis. The adsorption properties of the stationary phases were investigated by determining differential enthalpies, entropies, and free energies of adsorption for a selected group of organic moieties. Rate theory was used to examine further the interaction between the molecular probes and the tailored supports. Relative peak broadening was measured both as a function of flow rate and temperature to provide a chromatographic evaluation of molecular probe-adsorbent interaction occurring during the chromatographic process. Results indicated that the single-molecule moieties used as tailoring agents served as excellent deactivating agents but produced no significant changes in the selectivity of the adsorbents. Pellicular beads were synthesized by using 4-vinylpyridine as a linking agent between the alumina substrate and a series of polymers. The polymers used in this study were polystyrene, polymethylmethacrylate, and polyacrylonitrile. Each type of polymer-coated bead was prepared at different loading levels. Scanning electron microscopy was used to examine the gross change in the surface and elemental analysis used to determine the polymer loading. The adsorption properties of the polymeric pellicular supports were studied by determining the aforementioned thermodynamic quantities and by rate theory. The relative peak broadening was mentioned as a function of polymer type, loading, flow rate, and temperature. The chromatographic behavior of the selected molecular probes on the pellicular supports was sensitive to polymer type and loading. It was established that alumina can be modified with amines and pyridines and that a molecule possessing a nitrogen atom and a polymerization site can be used as an adhesive interface to chemically link polymeric phases to alumina. Currently, there are no commercially available modified aluminas. It has been demonstrated here that the preparation of such supports is feasible and can lead to chromatographically useful products.