Studies in pressurized planar electrochromatography

Allyson L Novotny, Purdue University

Abstract

Pressurized Planar Electrochromatography is a fast and efficient planar chromatographic technique that was recently developed at IUPUI. The mobile phase is driven by electroosmotic flow while the system is pressurized in a manner that allows heat to flow between the sorbent layer and the pressurizing medium. PPEC retains all of the attractive features of classical Thin-Layer Chromatography. Further advantages of Pressurized Planar Electrochromatography include the ability to separate multiple samples simultaneously, separate samples that have been spotted in a two-dimensional array across the plate, and run separations on multiple plates simultaneously. A prototype apparatus for performing Pressurized Planar Electrochormatography is described in this thesis, and was used to demonstrate that this technique is significantly faster and more efficient than classical Thin-Layer Chromatography. An example is shown in which a 24-fold enhancement in the speed of separation is achieved with Pressurized Planar Electrochromatography. Reproducibility with this apparatus was poor, and several changes were made to the apparatus and operating procedure to improve this. The second prototype apparatus is described in detail in this thesis. It was shown that the migration distance of neutral analytes increases with applied voltage, percent organic modifier, conditioning temperature, soak time, and buffer concentration, while migration distance decreases with applied pressure. The highest efficiency in Pressurized Planar Electrochromatography is achieved at an intermediate temperature. This behavior is ascribed to high resistance to mass transfer at lower temperatures and increased diffusion at higher temperatures. Efficiency, as measured by the number of theoretical plates increases with increasing migration distance. Under appropriate conditions, efficiencies as high as 94,000 plates per meter were achieved. This thesis also described the dependence of efficiency in Pressurized Planar Electrochromatography on the applied voltage (used as a surrogate for flow rate), and applied pressure, the temperature, and the buffer concentration and pH of the mobile phase. Results are presented as plots of the height equivalent of a theoretical plate versus applied voltage. With the exception of separations at 0°C, the highest efficiency is observed at the highest applied voltage. Desorption electrospray ionization is a new mass spectrometry method that allows analytes to be ionized directly from a TLC plate after PPEC. The detection and identification of the analytes of a five component mixture separated in one minute was achieved.

Degree

Ph.D.

Advisors

Nurok, Purdue University.

Subject Area

Analytical chemistry

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