No description available.

For a number of reasons, miniaturization of chromatographic columns has been a general trend over the past three decades. Methods designed to enhance selectivity and efficiency can offer improved separation power and speed, expanding on the advantages of miniaturized columns. This dissertation describes novel approaches in this direction, focusing on two areas: the development of affinity-type sorbents for capillary HPLC derived from molecular imprinted polymers (MIPs) and the study of perfusive electroosmosotic flow (EOF) and its effect on efficiency in capillary electrochromatography (CEC). MIPs are synthetic polymers capable of selectively binding a template molecule incorporated prior to polymerization. MIPs prepared using nortripyline, a tricyclic antidepressant drug, were employed to screen a simulated chemical library, consisting of a series of structural analogs and related compounds. A parameter was introduced to quantify the selective retention of the analytes. Library compounds containing the major structural features of the template (ring structure and pendant 2�� amine) exhibited the highest affinity for the MIP. The use of macroporous packings under conditions of electroosmotic perfusion can result in improved chromatographic efficiencies. In this work, the performance of CEC columns packed with particles having different nominal pore diameters was investigated. The results indicate that perfusive EOF can yield significant gains in efficiency and speed, especially when wide pore packings and dilute buffers are employed. A model was developed that estimates the extent of perfusive EOF expressed as an effective particle diameter, d[subscript p,eff] The results suggest that the observed efficiency gains are not entirely due to smaller d[subscript p,eff] values and could perhaps be due to a decreased A term in the wide pore packings. The electrical conductivity of CEC columns was used to assess intraparticle flow permeability under conditions of perfusion. Results for the narrow pore (100 ��) column were in agreement with theory for nonporous spheres, indicating intraparticle current was negligible, while the wide pore (1000 and 4000��) columns exceeded theoretical values by a factor of two. These results provide evidence of the existence of "through-pores" and that intraparticle flow permeability (and potential for improved efficiency with perfusion) is greatest with wide pore packings. / Graduation date: 2001

Thesis (Ph. D.)--Florida State University, 2005. / Advisor: Dr. John G. Dorsey, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed Sept. 19, 2005). Document formatted into pages; contains xxii, 154 pages. Includes bibliographical references.

Over the last decade, the miniaturization of analytical systems has become an increasingly important and interesting research area. Miniaturized systems offer many advantages, including reduced reagent and sample consumption, shorter analysis times, portability and disposability. This dissertation describes novel approaches in this direction, focusing on two areas: the miniaturization of existing column chromatographic systems and the development of microfluidic systems in which the separation is performed in a channel on a microchip. A new type of methacrylate-based monolithic capillary columns for liquid chromatography and capillary electrochromatography were prepared within the confines of fused-silica tubing using Starburst dendrimers to affect porosity. The polyamidoamine (PAMAM) dendrimers were incorporated into a solution of functionalized monomer, cross-linker, solvents, and polymerization initiator. Thermal polymerization, followed by the removal of solvent and dendrimers, produced a continuous rod of polymer with uniform porosity. Different column porosities were obtained by varying the amount of the dendrimer template. The chromatographic performance of these monolithic columns was evaluated using a peptides mixture obtained by tryptic digestion of chicken egg lysozyme. A distinct advantage of polymer monolithic stationary phases over conventional packed chromatographic beds is the ability to prepare them easily and rapidly via free radical polymerization within the channels of a microfluidic device. In this work, continuous polymeric beds were prepared within a channel of three different microchip substrates: glass, poly(dimethylsiloxane) and polycarbonate. The methacrylate-based monolith was cast in-situ via UV-initiated polymerization. The functionalization of the inner wall of the channel with methacryloyl groups enabled the covalent binding of the monolith to the wall. The morphology of the wall-anchored monolith was studied by SEM of chip sections, and by SEM of an extruded segment of non-anchored monolith from a separate chip. / Graduation date: 2005

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 145-148).

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains viii, 46 p. : ill. Includes abstract. Includes bibliographical references (p. 45-46).

Means of achieving rapid, efficient separations of analytes are explored in detail, with particular emphasis on the use of chromatographic and electrophoretic theory as an aid in system design and optimization. The benefits of miniaturization of chromatographic systems are assessed. First, the utility of semi-micro Ion Chromatography is explored by the manufacture of 2mm ID analytical and suppressor columns and a micro-conductivity cell. The quality of the columns and detector cell are evaluated by the separation of a test mixture and the calculation of peak variance contribution of the detector cell. The use of readily available analytical scale instrumentation for semi-micro IC is demonstrated. Next, a further downsizing of the IC system is described, in which 530μm ID fused silica tubing is utilized for column manufacture. In this case, a suppressor column is not used and UV detection is employed in the analysis of nucleoside monophosphates. Again, column performance characteristics are measured and noted. Application of this system to the separation of a hydrolysed nucleic acid sample demonstrates the feasibility of the technique to the analysis of volume-limited samples in low concentration with notable sensitivity. The benefits of a miniaturized liquid chromatographic system under pressure-driven flow is studied and the improved permeability of micropacked capillary columns is exploited in the manufacture of several 25 to 30cm columns which achieve high efficiencies with relatively low pressure drops. Van Deemter plots illustrate the performance characteristics of the columns. Finally, electroosmotic flow is studied as the motive force for liquid chromatographic separations. This combination of two techniques, packed capillary liquid chromatography and capillary electrophoresis, results in a system which achieves good resolving power through maximization of selectivity and efficiency. / Ph. D.

Thesis (M.S.)--University of North Carolina at Greensboro, 2007. / Title from PDF t.p. (viewed Mar. 11, 2008). Directed by G. Brent Dawson; submitted to the Dept. of Chemistry. Includes bibliographical references (p. 67-69).

Thesis (Ph. D.)--Brigham Young University. Dept. of Chemistry and Biochemistry, 2004. / Includes bibliographical references.

This dissertation focuses on the development of hand-portable capillary liquid chromatography (LC) instrumentation. In this work, battery-operable nano-flow pumping systems (isocratic and gradient) were developed and integrated with portable UV-absorption detectors for capillary LC. The systems were reduced in size to acceptable weights and power usage for field operation. A major advantage of the pumps is that they do not employ a splitter, since they were specifically designed for capillary column use, thereby greatly reducing solvent consumption and waste generation. UV-absorption detectors were specifically designed and optimized for on-column detection to minimize extra-column band broadening. Initially, an isocratic nano-flow pumping system with a stop-flow injector was integrated with an on-column UV-absorption detector (254 nm). The pumping system gave excellent flow rate accuracy (<99.94%) and low percent injection carry-over (RSD 0.31%) suitable for quantitative analysis. Using sodium anthraquinone-2-sulfonate, the detector gave an LOD (S/N = 3) of 0.13 µM, which was 12 times lower than a commercial UV-absorption detector. Reversed-phase separations of a homologous series of alkyl benzenes was demonstrated. Further miniaturization of UV-absorption detection was accomplished using a 260 nm deep UV LED. The detector was small in size and weighed only 85 g (without electronics). No optical reference was included due to the low drift in the signal. Two ball lenses, one of which was integrated with the LED, were used to increase light throughput through the capillary column. Stray light was minimized by the use of a band-pass filter and an adjustable slit. Signals down to the ppb level (nM) were easily detected with a short-term noise level of 4.4 µAU, confirming a low limit of detection and low noise. The detection limit for adenosine-5'-monophosphate was 230 times lower than any previously reported values. Isocratic separations of phenolic compounds were performed using a poly(ethylene glycol) diacrylate monolithic capillary column. Finally, a novel nano-flow gradient generator integrated with a stop-flow injector was developed. Gradient performance was found to be excellent for gradient step accuracy (RSD < 1.2%, n = 4) and linear gradient reproducibility (RSD < 1.42%, n = 4). Separations of five phenols were demonstrated using the nano-flow gradient system. Efforts to develop a 405 nm laser diode-based UV-absorption detector for hemoglobin analysis were described.