CEs - An animation detailing all three of these modes of...

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An animation detailing all three of these modes of capillary electrophoresis can be found here: www.shsu.edu/%7Echm_tgc/sounds/CEs.mov . Similarities in these three modes of capillary electrophoresis All analytes in the three methods I describe here, primarily move via electroosmotic flow (EOF, see my other animations on CE). That means, cations, anions, and neutral species move from the injector reservoir to the detector end of the capillary via EOF. CE methods in which analytes move against the EOF are less common because their analysis time is longer. With that said, it's only CZE that uses "simple" buffer solutions for separation. The other two methods described below use either conductivity gradients, when separating simple ions (CITP), or a pH gradient to separate amphiprotic compounds, molecules that can accept or donate a proton (CIEF). And one more point: although EOF is used in all methods, only CZE separates analytes during EOF. The other two methods use an electrical potential to achieve the separation, but EOF is only used in the last step to flow analytes pass the detector and off the column to waste. In all of the following schematics, the long blue tube represents the entire CE capillary (whose diameter is really small). The potential voltage is applied across this capillary. Unlike capillary gas chromatography, the small diameter capillary used in CE is not very long at all, usually less than a meter, and modern CE instruments have an automatically controlled cooling system to remove joule heating that is produced by the electrophoretic process itself. Capillary Zone Electrophoresis (CZE) CZE analytes move in the EOF but separate into bands because of differences in their electrophoretic mobilities, µ . Differences in µ make each analyte's overall migration velocity slightly different, and difference in migration velocity = separation. µ 's are roughly a function of analyte charge and frictional and size differences. In the adjacent image, three peaks are traveling down the capillary from the beginning of the capillary on the left to the detector and exit reservoir on the right (again, this is a simple schematic). In this system, an absorption detector would work if the analytes have good molar absorption at wavelengths the detector has available (usually in the UV). If the analytes are poor absorbers then a strong UV absorber can be added to the run buffer and the decrease in absorption—when the analytes pass the detector—can be used to detect the
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analytes. This last is called indirect absorption . In the image above while the three analytes are still on the capillary, the electropherogram at the bottom
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This note was uploaded on 03/03/2012 for the course CHEM 100 taught by Professor Chasteen during the Fall '06 term at Sam Houston State University.

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CEs - An animation detailing all three of these modes of...

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