Year of Award

2017

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Chemistry (Analytical/Environmental Option)

Department or School/College

Department of Chemistry and Biochemistry

Committee Chair

Christopher Palmer

Commitee Members

Earle Adams, Orion Berryman, Michael DeGrandpre, Tony Ward

Keywords

cationic latex nanoparticles, electrokinetic chromatography, explosives, RAFT polymerization

Abstract

Electrokinetic chromatography (EKC) is a powerful analytical technique that uses the instrumentation of capillary electrophoresis (CE) and the principles of chromatography to separate ionic and neutral analytes. A capillary is filled with background electrolyte (BGE), and when a voltage is applied ionic species migrate to the electrodes. Neutral compounds have no mobility, so a pseudo-stationary phase (PSP) is added to the BGE that consists of an ionic group to provide mobility and a hydrophobic group to interact with analytes. Analytes interact with the PSP which changes their apparent mobilities, leading to a separation. It is possible to coat the negatively charged silica surface of a capillary with a cationic polymer, reverse the polarity of the electrodes, and use a cationic PSP to perform separations. This is the subject of this dissertation.

RAFT polymerization was used to create diblock copolymers that self-assemble into latex nanoparticles and used as PSPs for EKC. Two cationic monomers, [2-(Acryloyloxyl)ethyl]trimethyl-ammonium chloride (AETMAC) and (3-Acrylamidopropyl)trimethylammonium chloride (APTAC), and three hydrophobic monomers, butyl acrylate (BA), ethyl acrylate (EA), and methyl acrylate (MA) were investigated. RAFT polymerization was an effective way to create the desired materials, and several techniques were used for characterization. Unexpected band broadening was observed when the nanoparticles were used as PSPs, so an additional cationic homopolymer, PAETMAC, was needed to coat the capillaries to prevent hydrophobic interactions at the capillary surface. The linear solvation energy relationships (LSER) model was used to compare different cationic latex nanoparticles. The choice of cationic block did not affect selectivity, but nanoparticles with MA cores showed a significant difference from nanoparticles with EA or BA cores. Finally, PAETMAC coated capillaries and cationic latex nanoparticles were used to separate anions and nitro compounds found in explosives residues. Separations can be performed in less than 10 minutes. The hydrophobic anions perchlorate and thiocyanate are retained by the nanoparticles, and acetonitrile was added to the BGE to reduce band broadening of these analytes. Future directions for this work include further characterization of the diblock copolymers, further optimization of the explosives separation, and the development of a portable fluorescence quenching detection system.

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© Copyright 2017 Julie Rebecca McGettrick