Novel approaches to enhancing selectivity and efficiency in microscale liquid chromatography Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/d791sj41g

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  • 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 Å) column were in agreement with theory for nonporous spheres, indicating intraparticle current was negligible, while the wide pore (1000 and 4000Å) 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.
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