DOI
https://doi.org/10.25772/PQ7K-KR70
Author ORCID Identifier
https://orcid.org/0000-0003-3060-8220
Defense Date
2021
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Maryanne M Collinson
Abstract
Recent research in liquid chromatography (LC) has led to the development of new methodologies to further improve sample analysis. Non-uniform stationary phases are one such area that focuses on developments in selectivity and efficiency of stationary phases. Within this subset of stationary phases are two major focuses: two-dimensional liquid chromatography (2D-LC) and continuous stationary phase gradients that are the basis of this work.
In this work, LC simulation software was adapted to simulate chromatograms based on experimental and modeled injection profiles. This was done by measuring the injection profiles from a 2D-LC active solvent modulation valve using a variety of injection loop sizes. Next, modeling with a convolution of Gaussian and exponential decay functions was used to parameterize these profiles and integrate these functions into an in-house chromatographic simulator. This work has improved simulation-driven approaches that are both accurate and fast enough to rapidly explore candidate separation conditions prior to doing experimental 2D-LC separations of real samples.
Another area of development to improve separation and resolution in LC has been the development and use of continuous stationary phase gradients where the density of one or more surface ligands varies gradually within a single column. These novel stationary phases have demonstrated unique selectivity of analytes, which has been attributed to neighboring ligand effects during sample separation. One technique used to fabricate these gradients has involved the controlled rate infusion of trifluoroacetic acid to cleave existing ligands from a commercial column in a time dependent manner through acid hydrolysis. This methodology has been reported for the fabrication of continuous C18 gradients on particle packed LC columns.
This work has expanded on this previous development by investigating the transfer of this fabrication method to phenyl and phenyl-hexyl particle packed columns. Specifically, modification of two types of phenyl based stationary phases will be discussed. These columns were evaluated chromatographically for their stability, hydrophobicity, and silanol activity. The chromatographic behaviors of these columns were characterized using mixtures of probe solutes. Additionally, the stability, hydrophobicity, and silanol activity of each of these stationary phases were determined. The stationary phase ligand profile was also established using thermogravimetric analysis. Ultimately, this work provides a greater understanding of the feasibility of generating these continuous gradient stationary phases to potentially improve selectivity and reuse LC columns with a variety of ligand types.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-7-2021