Quant_Lect_15_CE - So for big molecules D is small but EO...

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Capillary (and a bit of Planar) Electrophoresis I. Ionic motion, in vacuum vs. subject to viscous drag. Stokes-Einstein diffusion: . Viscosity in poise, mobility in cm 2 V -1 s -1 . Diffusion coefficient relates to mobility via II. Electro-osmotic flow. Helmholtz-Smoluchowski eqn. Zeta potential set by structure of electrical double layer. Double-layer thickness ~ 100 Angstroms for ~ mM solution. Planar/plug flow vs. Poissieulle flow (see P. H. Paul, M. G. Garguilo, and D. J. Rakestraw, Anal. Chem. 70 , 2459-2467 (1998)). III. Resistivity, resistance, conductivity, electric field, heat conduction, and heat generation. P = i 2 R At constant voltage, P = V 2 /R = . Effect of radial temperature gradients. Protons as most mobile species; pH typically confined between 3 and 10. IV. Why capillary electrophoresis works. Capillary gel, capillary zone. Number of theoretical plates ~
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Unformatted text preview: . So for big molecules, D is small, but EO flow makes mobility reasonable. Then higher voltage gives higher number of plates. V. Mobile phase modifiers: surfactants, buffers VI. Detection issues: the need for high sensitivity, low background, and low absolute detection limit. Fluorescence, absorption, amperometry, mass spectrometry (typically with electrospray injection) VII. Sampling modes: electrokinetic, hydrodynamic/siphoning, pressure VIII. Controlling electro-osmotic flow: ionic strength, capillary coating. IX. Planar electrophoresis (1 or 2 dimensional) also works on the basis of mobility, but can include pH gradients, size-exclusion/gel permeation for size filtering. Page 1 of 1 Capillary Electrophoresis 12/8/2010 https://courses.las.illinois.edu/file.php/173/Quant_Lect_15_CE.htm...
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This note was uploaded on 04/02/2012 for the course CHEMISTRY 222 taught by Professor Mcdonald during the Fall '11 term at University of Illinois, Urbana Champaign.

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