| This work investigates the properties and applications of acetonitrile-based media in capillary electrophoresis (CE). Because of the unusual chemical and physical properties that characterize acetonitrile, certain electrophoretic separations may be achieved in this solvent that are not possible with other commonly-used CE solvents. Presented in this work are the separations that were obtained using acetonitrile-based media, as well as some of the studies that elucidate some of the factors responsible for the observed migration behavior of the separated solutes.; There are two main research projects that comprise this volume. First, the separation of neutral solutes--polycyclic aromatic hydrocarbons (PAHs), in particular--was carried out using charge-transfer type interactions with planar organic cations. It was observed that the tropylium and 2,4,6-triphenylpyrylium ions afforded the best separations of these neutral solutes. Moreover, it was found that the polarizability of the solute molecule (as described by the number of rings in the PAH molecule) was the primary factor that influenced the degree of the charge-transfer interactions with the cations. Other factors that were found to affect the mobility of the PAH-cation complex include the concentration of the cation employed in the separation; the number of phenyl substituents attached to the pyrylium cation; and the number, position, and nature of any substituents attached to the parent PAH molecule. The choice of counterion, on the other hand, had no significant effect on the mobility of the PAH-cation complex.; The second project discussed in this volume deals with the acetonitrile-based CE separation of ionizable compounds. It was discovered that through the use of a dilute buffer consisting of a carboxylic acid and tetrabutylammonium hydroxide (a strong base) in acetonitrile, efficient separations of a variety of organic acids could be carried out in under six minutes. The combined effects of deprotonation and heteroconjugation coupled with acetonitrile's low viscosity were responsible for these effects. Equations were derived describing the relationship between the buffer concentration and the observed mobilities. Based on this relationship, as well as the p{dollar}Ksb{lcub}rm a{rcub}{dollar} values of the analytes and the buffer pH, the heteroconjugation constants for several analyte-buffer combinations were calculated. Substituted phenols, benzoic acids, and dipeptides were among the acids that were separated using this technique. lt was also found that, through the use of a buffer containing a strong acid and a weak base, the separation of weak organic bases could likewise be obtained. |
