The role of structure, orientation and composition of chemically tailored surfaces in differential migration techniques.

Abstract

Control of separation processes which occur at solid-liquid interfaces can be achieved by understanding the interactions which occur at these interfaces. Because of its many desirable bulk characteristics, silica is the solid support of choice for many separation applications. Utilizing various differential migration techniques, control of the separation at different silica surfaces was investigated through irreversible chemical modification of the surface, the use of a dynamic modifier, and through physicochemical alteration of the silica surface. A new bonded phase was prepared by reacting γ-(3,4 methylene dioxyphenyl) propyldimethylchlorosilane--synthesized from safrole and dimethylchlorosilane--with porous silica yielding a non-traditional bonded phase which maintained some similarity with traditional alkyl bonded phases while also possessing distinct differences. Through the use of diagnostic chromatography this surface was shown to demonstrate unique selectivity towards polar analytes when compared with an octyl and phenyl surface under the same solvation conditions. A thermal study utilizing diagnostic chromatography was also used to demonstrate the impact of orientation on retention at this surface. The large scale separation of C₆₀ and C₇₀ was accomplished using a batch process utilizing a traditional bonded phase under normal phase condiitons. Both the kinetics and thermodynamics of the separation were improved through the addition of a dynamic modifier to the running solvent. Macroscopic quantities of pure C₆₀ and C₇₀ are readily obtained using this approach. Control of electroosmotic flow in silica capillaries was demonstrated by chemically tailoring the surface with a series of novel silane modifiers. Although changes in electroosmotic flow velocity were observed, the ultimate goal of flow reversal was not achieved. Finally, a new ISRP surface was prepared by monoatomic oxygen treatment of large (63-90μm) irregularly shaped modified silica particles. This new ISRP was evaluated to determine if the more technically demanding but practically useful treatment of high efficiency particles for use in direct injection HPLC should be pursued.