## LSU Historical Dissertations and Theses

1992

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

Joe P. Foley

#### Abstract

Micellar electrokinetic capillary chromatography (MECC) is a rapidly growing technique allowing separation of electrically neutral compounds with the high separation efficiencies typically observed in capillary zone electrophoresis. This technique is still in its infancy and subsequently suffers from several inherent problems which must be addressed such as the limited range of solute elution and clear protocol for optimization of separations. This work addresses these problems with primary emphasis on using mixed nonionic/anionic surfactant systems as opposed to pure surfactants. In Chapter One, the fundamental theory behind MECC is discussed along with a brief synopsis of previous studies involving different surfactant systems, modification of micellar media with organic solvents, and the effect of mobile phase variation on the solute elution range. Chapter Two addresses resolution optimization by adjusting surfactant concentration. Two surfactant systems, pure SDS and Brij 35/SDS, were used in this study. The Brij 35/SDS system was advantageous due to higher separation efficiency, more constant elution ranges $\rm (t\sb{mc}/t\sb{o}),$ and resolution optimization between hydrophilic analytes; SDS found favor for optimizing the resolution between moderately hydrophobic solutes. Chapter Three is a more in-depth comparison of SDS and Brij 35/SDS surfactant systems. Results indicate that in the Brij 35/SDS system, solute/micellar surface interactions play a key role in retention of certain compounds. Also, changes in electroosmotic and micellar electrophoretic velocities with varying Brij 35 concentration indicate the possibility of an infinite elution range in this system. Chapters Four and Five discuss the effects of three organic modifiers; acetonitrile, methanol, and l-propanol; upon the retention characteristics of an n-alkylphenone homologous series for the SDS and Brij 35/SDS systems, respectively. Our results point to greater structural stability for Brij 35/SDS micelles. Also, the polyoxyethylene surface layer of Brij 35/SDS micelles may influence solute partitioning via reduced solute/micellar surface interactions. Finally, the appendix reports our work on the combination of secondary chemical equilibrium (SCE)-LC sequentially with reversed-phase HPLC to provide multimodal separation of complex samples on a single column.

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