Christine L. Copper

Separation of stereoisomers of aminoglutethimide using three capillary electrophoretic techniques

A novel approach to capillary electrokinetic chromatography involving differential distribution between neutral and charged cyclodextrins is described for the separation of the enantiomeric pair of the drug aminoglutethimide. For comparison purposes, micellar electrokinetic capillary chromatography and capillary electrophoresis with neutral cyclodextrin additives are also evaluated for this separation. The three techniques are compared in terms of their ability to resolve the two enantiomers. At pH 9, where aminoglutethimide is neutral, the enantiomers were resolved using a running buffer containing 5 mM β-cyclodextrin, and 50% (v/v) methanol. At the same pH, micellar electrokinetic capillary chromatography, using a running buffer containing 50 mM sodium dodecyl sulfate and 17.5 mM β-cyclodextrin, only partially resolved the enantiomers. However, at pH 3, where aminoglutethimide is ionized, the enantiomeric pair was separated using capillary electrophoresis with either 10 mM α-cyclodextrin or 5 mM γ-cyclodextrin added to the running buffer. Enantiomeric separations, by way of the three electrophoretic capillary chromatographic techniques mentioned above, are presented and mechanisms of chiral recognition of aminoglutethimide by cyclodextrins under various experimental conditions are also discussed.

Characterization of Polyaromatic Hydrocarbon Mixtures by Micellar Electrokinetic Capillary Chromatography

Abstract The utilization of micellar electrokinetic capillary chromatography (MECC) for analyses of mixtures of polycyclic aromatic hydrocarbons (PAH), including those isolated from complex samples such as shale oil, is described. Factors that influence separation performance, including retention, selectivity, and efficiency, are examined. The use of different micellar systems and mobile phase additives, such as organic solvents to effect retention and cyclodextrins to exploit size selectivity, are investigated. In addition, narrow-bore capillaries and laser fluorimetry are used to enhance separation efficiency and detection sensitivity. The ability to accommodate real samples is examined and compared to HPLC.

Separation Behavior of Common Fullerenes in Cyclodextrin-HPLC Based on Computationally-Derived Interaction Energies

Abstract Molecular modeling and basic thermodynamic considerations are used to explain previously reported HPLC retention behavior of C60 and C70 using a σ-cyclodextrin stationary phase. Evidence thatinclusion complex formation between the fullerene and σ-cyclodextrin is not essential to resolve C60 and C70 is presented. Computationally-derived interaction energies alone do not correlate with the observed HPLC retention behavior. However, interaction energy values combined with mobile phase solubility data, non-inclusion interactions, and a discussion of entropy changes due to phase transfer provide a more thorough explanation of retention in this separation system.