Electrophoretic mobility Electrophoresis

First, solutes with larger electrophoretic mobilities (in the same direction as the electroosmotic flow) have greater efficiencies thus, smaller, more highly charged solutes are not only the first solutes to elute, but do so with greater efficiency. Second, efficiency in capillary electrophoresis is independent of the capillary s length. Typical theoretical plate counts are approximately 100,000-200,000 for capillary electrophoresis. 

A form of capillary electrophoresis in which separations are based on differences in the solutes electrophoretic mobilities. 

Electroultrafiltration (EUF) combines forced-flow electrophoresis (see Electroseparations,electrophoresis) with ultrafiltration to control or eliminate the gel-polarization layer (45—47). Suspended colloidal particles have electrophoretic mobilities measured by a zeta potential (see Colloids Elotation). Most naturally occurring suspensoids (eg, clay, PVC latex, and biological systems), emulsions, and protein solutes are negatively charged. Placing an electric field across an ultrafiltration membrane faciUtates transport of retained species away from the membrane surface. Thus, the retention of partially rejected solutes can be dramatically improved (see Electrodialysis). 

Electroosmotic flow in a capillary also makes it possible to analyze both cations and anions in the same sample. The only requirement is that the electroosmotic flow downstream is of a greater magnitude than electrophoresis of the oppositely charged ions upstream. Electro osmosis is the preferred method of generating flow in the capillary, because the variation in the flow profile occurs within a fraction of Kr from the wall (49). When electro osmosis is used for sample injection, differing amounts of analyte can be found between the sample in the capillary and the uninjected sample, because of different electrophoretic mobilities of analytes (50). Two other methods of generating flow are with gravity or with a pump. 

The standard Rodbard-Ogston-Morris-Killander [326,327] model of electrophoresis which assumes that u alua = D nlDa is obtained only for special circumstances. See also Locke and Trinh [219] for further discussion of this relationship. With low electric fields the effective mobility equals the volume fraction. However, the dispersion coefficient reduces to the effective diffusion coefficient, as determined by Ryan et al. [337], which reduces to the volume fraction at low gel concentration but is not, in general, equal to the porosity for high gel concentrations. If no electrophoresis occurs, i.e., and Mp equal zero, the results reduce to the analysis of Nozad [264]. If the electrophoretic mobility is assumed to be much larger than the diffusion coefficients, the results reduce to that given by Locke and Carbonell [218]. 

Overbeek, JTG Wiersema, PH, The Interpretation of Electrophoretic Mobilities. In Electrophoresis, Theory, Methods and Applications Bier, M, ed. Academic Press New York, 1967 1. 

Waldmann-Meyer, HK, Protein Ion Equilibria, Total Evaluation of Binding Parameters and Net Charge from the Electrophoretic Mobility as a Function of Ligand Concentration. In Recent Developments in Chromatography and Electrophoresis Frigerio, A McCamish, M, eds. Elsevier Scientific Amsterdam, 1980 Vol. 10, p 125. 

Att eZcven y-cJuiin voA nts, discovered thus far, exhibit a change In electrophoretic mobility, and starch gel electrophoresis Is the recommended method for their detection. Quantitation of the variant can best be done by chromatography on columns of either DEAE-Sephadex or CM-Cellulose. The quantities of some variants In heterozygotes differ greatly. For Instance, the relative amount (expressed In %F /Fxotal) varies from 20-25% (F-Malta-I) to 10-15% (most Y C >aln variants) to 5-6%... 

The defnon6ttLOtion 0 -chain vaAijant6 In heterozygotes Is complicated by the presence of the large amount of Hb-F. Another obstacle Is the nearly Identical electrophoretic mobilities of Hb-A and the minor Hb-Fi component. Despite these difficulties, abnormalities such as AS, SS, AC, CC, SC, and others can readily be detected using cellulose acetate electrophoresis, starch gel electrophoresis, acid agar electrophoresis, and by CM-Cellulose microchromatography to be described In a separate section. 

The presence of Individual chains In a hemoglobin variant can also be demonstrated by electrophoresis at alkaline pH after the protein has been dissociated Into Its subunits through exposure to 6 M urea In the presence of 3-mercaptoethanol. The buffer is either a barbital buffer or a tris-EDTA-boric acid buffer, pH 8.0 - 8.6, and contains 6 M urea and 3-niercapto-ethanol. Dissociation of the hemoglobin Into subunits Is best accomplished In a mixture of 1 ml 10 g% Hb (or whole hemolysate), 4 ml 6 M urea barbital or tris-EDTA-boric acid buffer, and 1 to 1.5 ml 3-mercaptoethanol. After 30 minutes to 1 hour the sample Is subjected to cellulose acetate or starch gel electrophoresis. Each chain has a specific mobility and an alteration In electrophoretic mobility easily Identifies the abnormal chain. 

Electrophoresis occurs in electrolyte solutions, where a competition of two forces, the electric force Fe and the frictional force Ff, are in equilibrium. The relationship of the two forces determines the electrophoretic mobility of the compounds ... 

Williams, B. A. and Vigh, G., Effect of the initial potential ramp on the accuracy of electrophoretic mobilities in capillary electrophoresis, Anal. Chem., 67, 3079, 1995. 

Grossman, P. D., Colburn, J. C., and Lauer, H. H., A semiempirical model for the electrophoretic mobilities of peptides in tree-solution capillary electrophoresis, Anal. Biochem., 179, 28, 1989. 

Rickard, E. C., Strohl, M. M., and Nielsen, R. G., Correlation of electrophoretic mobilities from capillary electrophoresis with physicochemical properties of proteins and peptides, Anal. Biochem., 197, 197, 1991. 

Tinland, B., Pernodet, N., and Weill, G., Field and pore size dependence of the electrophoretic mobility of DNA A combination of fluorescence recovery after photobleaching and electric birefringence measurements, Electrophoresis, 17, 1046, 1996. 

McKillop, A.G., Smith, R.M., Rowe, R.C., and Wren, S.A.C., Modeling and prediction of electrophoretic mobilities in capillary electrophoresis separation of alkylpyridines, Anal. Chem. 71, 497, 1999. 

If the electric field E is applied to a system of colloidal particles in a closed cuvette where no streaming of the liquid can occur, the particles will move with velocity v. This phenomenon is termed electrophoresis. The force acting on a spherical colloidal particle with radius r in the electric field E is 4jrerE02 (for simplicity, the potential in the diffuse electric layer is identified with the electrokinetic potential). The resistance of the medium is given by the Stokes equation (2.6.2) and equals 6jtr]r. At a steady state of motion these two forces are equal and, to a first approximation, the electrophoretic mobility v/E is... 

Capillary zone electrophoresis, an up-to-date high resolution separation method useful for proteins and peptides, has been shown to be a useful method for determining electrophoretic mobilities and diffusion coefficients of proteins [3], Diffusion coefficients can be measured from peak widths of analyte bands. The validity of the method was demonstrated by measuring the diffusion coefficients for dansylated amino acids and myoglobin. 

Y Walbroehl, J Jorgenson. Capillary zone electrophoresis for determination of electrophoretic mobilities and diffusion coefficients. J Microcolumn Separ 1 41, 1989. 

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