Author

Saba Aslani

Graduation Semester and Year

2023

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Daniel W Armstrong

Abstract

This dissertation focuses on developing improved methods and a better understanding of gas and liquid chromatographic separation of isotopic isomers and enantiomers. The second and third chapters of this thesis discuss analytical determination of isotopic isomers using gas chromatography. Deuterated compounds have found applications in many fields. They are used in drug discovery due to increased stability and bioavailability and reduced toxicity of the deuterated drug molecules. Also, deuterated compounds are used to investigate reaction mechanisms and rate determining steps. One of the methods of synthesizing deuterated compounds is starting from lower molecular weight deuterated building blocks. Therefore, analysis and separation of these small molecular weight analytes is important. Chapter two is the most comprehensive analysis in separation of deuterated compounds using gas chromatography yet reported. It provides the optimum conditions for separation of 46 pairs of deuterated isotopologues after examination of 12 stationary phases of different polarities. Chapter three describes the factors that affect chromatographic retention and isotope effects since the mass difference between deuterated and protiated analytes is not the only contributing factor for such GC separations. The position of deuterium atom also plays a role in chromatographic isotope effects mainly though inductive and resonance effects. The fourth chapter describes the second-generation (targeted) molecular rotational resonance (MRR) spectroscopy detector for gas chromatography (GC) for increased sensitivity and as the ultimate detector for structural determination and specificity among other GC detectors. Another improved feature of the targeted GC-MRR instrument, was wider molecular weight range and ability to analyze larger molecules (molecular weight range of 46−244 Da). These improvements were possible by incorporation of Fabry−Peŕot cavity and supersonic jet which provided immensely efficient cooling. As a result, the limits of detection of targeted MRR detector could be close to those of the classic GC thermal conductivity detector (TCD). Chapter five investigates enantioselective method development in HPLC and investigates the effect of trace amounts of water in normal phase liquid chromatography (NPLC) enantioselective separations. The presence of adventitious water in NPLC mobile phases has been frowned upon, due to irreproducibility in such analyses. We investigated this phenomenon by adding controlled amounts of water to various NPLC mobile phases. A large group of chiral pharmaceutical compounds were analyzed and investigated. The presence of water resulted in improved efficiency and resolution in most cases and reduced retention for all separations. Some might attribute these results to the polarity of the mobile phase. However, upon more thoroughly investigating the “water effect”, more factors were found to contribute. Chapter six introduces a new gas chromatography stationary phase which is made from dispersion of metal organic frameworks in ionic liquids. This is the first gas-liquid chromatography stationary phase that was able to provide sufficient retention for permanent gases like CO2, propane, and butane to separate them from air. Moreover, unique selectivities were observed for different mixtures of alkanes, alcohols, ethers, and ketones.

Keywords

Gas chromatography, Liquid chromatography, Chiral chromatography, Spectroscopy

Disciplines

Chemistry | Physical Sciences and Mathematics

Comments

Degree granted by The University of Texas at Arlington

Included in

Chemistry Commons

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