Degree Type

Dissertation

Date of Award

1991

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Edward S. Yeung

Abstract

A copper vapor laser two-photon excited fluorescence (LTPEF) detector for microcolumn liquid chromatography (LC) is described. The mass limit of detection (LOD) for the molecule 2-(4-biphenyl)-5-phenyl-1,3,4-oxidiazole (PBD) was measured and found to be 250 femtograms. This is better by a factor of 10[superscript]4 than that reported for PBD using an argon ion LTPEF detector;Two indirect fluorometric schemes are presented. First, a reversed phase open tubular capillary (OTC) of 50 [mu]m i.d. is dynamically modified with cetylpyridinium chloride to provide anion exchange sites. Sodium salicylate at 2.5 micromolar serves as the probe and is the eluent used to separate inorganic anions. The use of a double beam indirect fluorometric detector allows the anions to be detected with a baseline stability of 0.17%. A 2 picogram mass LOD (S/N = 2) for NO[subscript]3[superscript]- is reported;Similarly, 13-15 [mu]m i.d. OTC columns are dynamically modified with cetyltrimethylammonium bromide (CTAB) to provide anion exchange sites. Sodium salicylate (probe) at 2 micromolar is the eluent used to separate inorganic anions. Use of an indirect fluorometric detector allows the anions to be detected with a baseline stability ≥0.1%. In this case, a 10 femtogram mass LOD for NO[subscript]3[superscript]- to be achieved. Unmodified OTCLC columns are used to separate various alcohols. Using 2,7-dichlorofluorescein as the indirect probe, 72 femtograms of 1-nonanol can be detected;By incorporating CTAB into a buffer, enhancement of electroosmotic flow in polymer coated, reversed phase OTC columns is achieved. Using this flow, neutral isomers are separated with resolution >1 in all cases and efficiencies of 230,000 plates generated in less than 4 min. Hydrodynamic injection allows for picoliter samples to be introduced, and laser-based fluorescence detection allows a 0.75 attomole mass LOD to be measured;Finally, the separation of anions having similar electrophoretic mobilities by electroosmotically driven electrochromatography is described. Using an OTC column in conjunction with an ion-pairing buffer, anions separate based on differences in retention rather than differences in electrophoretic mobility. Resolution is easily controlled by varying the concentration of ion-pairing agent, tetrabutylammonium (TBA) cation. Mass transfer broadening is inherently smaller for this technique than for pressure driven OTCLC. A plate number (N) of 140,000 is reported on a 40-cm column in less than 5 min. This value of N is twice that for a similar chromatographic separation and nearly equal to that for a similar, but poorly resolved, capillary zone electrophoretic separation.

DOI

https://doi.org/10.31274/rtd-180813-12968

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

William D. Pfeffer

Language

en

Proquest ID

AAI9126236

File Format

application/pdf

File Size

156 pages

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