Author ORCID Identifier
0000-0002-5693-5505
Defense Date
2026
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Chemistry
First Advisor
Maryanne M. Collinson
Abstract
Modern separation challenges in liquid chromatography require strategies beyond conventional uniform stationary phases to improve separation performance. One promising approach is the use of stationary-phase gradients (SPGs), which introduce continuous variations in chemical properties along the separation medium. This work investigates phenyl-based SPGs as a strategy to enhance chromatographic performance through spatially varying surface chemistries. SPGs were developed and characterized on both planar and column chromatographic platforms using three complementary fabrication approaches. First, a vapor phase deposition method was employed to generate continuous gradients on thin-layer chromatography (TLC) plates using phenyldimethylchlorosilane (PDCS). Controlled vapor diffusion produced a functionalization gradient, confirmed by UV visualization and diffuse reflectance spectroscopy, resulting in improved selectivity and resolution compared to unmodified and uniformly modified plates. Second, a constructive in situ approach based on controlled-rate infusion (CRI) was used to fabricate SPGs within packed HPLC columns. Infusion of PDCS in dry toluene created a gradient in phenyl ligand density along the column, as verified by thermogravimetric analysis (TGA). These columns exhibited enhanced retention and distinct selectivity, enabling improved separation of small molecules and amphetamine derivatives, consistent with chromatographic simulations. Finally, a destructive CRI strategy was developed to generate SPGs on commercial phenyl columns through controlled hydrolysis of surface-bound ligands using trifluoroacetic acid. This approach produced an inverse ligand density gradient, confirmed by TGA. This gradient column showed altered retention characteristics and selectivity for analyte mixtures such as sunscreen analytes. Overall, this work establishes versatile methodologies for SPGs fabrication and highlights their potential to enhance selectivity and separation performance in liquid chromatography.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-4-2026