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Dissertation
Chiral microemulsion electrokinetic chromatography
Doctor of Philosophy (Ph.D.), Drexel University
Aug 2004
DOI:
https://doi.org/10.17918/etd-340
Abstract
Electrokinetic chromatography (EKC) has proven to be an invaluable tool for providing chiral separations. Its merits include fast, high efficiency, high resolution separations, which produce very little waste, consume minimal chemicals and are significantly more cost effective than its key competitors. EKC using chiral microemulsions (MEEKC) offers the additional advantages of increased solubility for analytes and additives as well as the ability to custom tune chiral resolution via elution window and retention factor optimization. Herein, the chiral resolution of various pharmaceutical compounds was explored using a microemulsion comprised of the chiral surfactant dodecoxycarbonylvaline (DDCV), 1-butanol as a co-surfactant, and ethyl acetate as a lipophilic phase (oil). Chapter 2 considers the effect of the lipophilic phase at a constant volume percentage or at a constant molarity. Chapter 3 reports the use of cyclodextrins, in combination with both a chiral (DDCV) and an achiral (sodium dodecyl sulfate) microemulsion, as a secondary pseudostationary phase. Importantly, the impact of background electrolyte (BGE) is critically assessed. Chapter 4 explores the effects of changing the surfactant concentration and/or phase ratio, BGE and applied voltage and Chapter 5 examines the thermodynamic quantities of transfer between the enantiomers and the DDCV microemulsion. Finally, in Chapter 6 DDCV microemulsion, butanol-modified micellar and micellar aggregates are compared using the same preparation technique and instrumental conditions. While the identity of the oil played only a minor role in analytical performance, surfactant concentration, BGE, applied voltage and the presence of a secondary pseudostationary phase all played major roles. Optimized method conditions provided resolution for all enantiomeric pairs (in some cases doubling in value upon optimization), superior retention and efficiencies that increased anywhere from 5 to 25 times their original values. In addition, van't Hoff analyses showed favorable enthalpic contributions to retention and selectivity, variable entropic contributions and an overall favorable Gibb's free energy of transfer between the analytes and the DDCV microemulsion. Finally, DDCV microemulsion and butanol-modified micelles behaved similarly using 2% DDCV, whereas greater differences were noted in comparison to the micellar phase. Further, when the comparison was performed using 4% DDCV, only the microemulsion resulted in a stable aggregate system.
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Details
- Title
- Chiral microemulsion electrokinetic chromatography
- Creators
- Melissa Danielle Mertzman - DU
- Contributors
- Joe Preston Foley (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- College of Arts and Sciences; Chemistry; Drexel University
- Other Identifier
- 340; 991014632200504721