Applications of nontraditional organized media in capillary electrophoresis

Capillary electrophoresis (CE) is a highly efficient separation technique capable of addressing many types of samples. CE has several advantages over conventional liquid-phase separation techniques: high efficiency, capability for high speed separations, low sample and mobile phase consumption, and selectivity control via solution chemistry. Of these points, two of the less investigated areas are selectivity control and separation speed. Selectivity in CE is largely determined by mobile phase additives. Two forms of CE predominate: capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC). CZE separates charged solutes based on electrophoretic mobility differences and MECC via differential association with electrophoretically-retarded micelles. This work investigates surfactant assemblies and cyclodextrins for suitability as selectivity modifiers in these techniques. While the potential versatility and efficiency of CE has attracted much attention to these techniques, several problems exist, in MECC, hydrophobic compounds are highly retained and difficult to resolve. Also, selectivity is limited because n-alkyl surfactant-formed micelles are usually employed. This work addresses these issues by investigating bile salt surfactants for use In MECC. Bile salts are biological detergents based on a hydroxy-substituted backbone. These surfactants are shown to produce a general reduction in capacity factor, k' and tolerate the presence of organic solvents to a greater extent than conventional surfactants (thus improving resolution for hydrophobic compounds). In addition, chiral separations are demonstrated for binaphthyl compounds using interactions with bile salt micelles. High-speed separations (<1 minute) can be achieved in MECC via the use of narrow-bore (25 μm) capillaries, high applied fields, and the relatively low k' values afforded by the use of bile salts. The high efficiencies attained in MECC are shown to facilitate rapid separations, and important experimental parameters are investigated for aflatoxin analysis. Cyclodextrins (CDs) can also be employed as mobile phase additives in CE. CDs are cyclic sugars capable of forming inclusion complexes that are influenced by molecular size and isomeric form of the analyte. CDs are demonstrated to be useful for chiral separations of charged compounds in the CZE mode. CD type and concentration are important in determining resolution. CDs are also employed in conjunction with surfactants for the MECC separation of methylanthracene isomers.