| The purpose of the research has been to obtain a fundamental understanding of chiral separation in nonaqueous capillary electrophoresis (NACE), and to enhance chiral selectivity and resolution in both aqueous and nonaqueous media by capillary electrophoresis. This goal is achieved by the alternation of separation solvents, the type of chiral selectors, the charges of solutes, and/or the direction of electroosmotic flow (EOF).; The first part of the research involves a fundamental study of chiral separation using cyclodextrins (CDs) in pure organic solvents, such as formamide (FA), and its derivatives. The results of chiral separation of some hydrophobic amines in three organic solvents, FA, N-methylformamide (NMF), and N,N-dimethylformamide (DMF), were compared to those in pure water and in 6 M urea water systems. The measured binding constants between the solutes and {dollar}beta{dollar}-CD decreased systematically from {dollar}sim 10sp4{dollar} to {dollar}sim10sp{lcub}-2{rcub}{dollar} in the following five systems: water, 6 M urea in water, FA, NMF, and DMF. The decrease in the binding constants results from the decrease in the polarity of the separation solvents. It was also found that in addition to the type and the concentration of CDs, other experimental parameters, such as apparent pH (pH*), ionic strength, temperature, and addition of tetraalkylammonium (TAA{dollar}sp+{dollar}) cations, can also affect separation selectivity and resolution. The application of charged {dollar}beta{dollar}-CDs to separate opposite charged analytes in FA showed that stronger binding between analytes and the opposite charged CD existed due to the additional electrostatic attractions. Compared to aqueous CE chiral separation of analytes with opposite charged CDs, the separation efficiency of the same type of application in FA was higher because peak tailing caused by electrodispersion was not as severe as in the aqueous CE. Enhanced efficiencies were observed at higher ionic strength due to reduction of mobility mismatch between the CD-analyte complexes and the co-ions in the buffer electrolytes. The first application of NACE chiral separation of a commercially available chiral drug, Actron, was also reported in FA by using a quaternary ammonium {dollar}beta{dollar}-CD.; The second part of the research involved the enhancement of chiral selectivity and/or resolution in aqueous media. The application of opposite charged CDs is very useful for the separation of compounds that interact weakly with neutral CDs (such as acebutolol, metanephrine, and normetanephrine, et al.), and the electrodispersion is not a server problem even at the high anionic CD concentrations. For amines that interact strongly with neutral CDs, the change in the compound charges from positive into neutral can eliminate electrodispersion. Thus, the separation efficiency can be enhanced. Finally, the enhancement of resolution by the counter-EOF setup makes it possible to separate enantiomers by the same charged CDs although the separation selectivity between enantiomers and the same charged CDs is likely to be smaller than that between enantiomers and opposite charged CDs. |
