Mobility in electrophoresis

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

Overbeek, J. Th. G., and Wiersma, P. H., The Interpretation of Electrophoretic Mobilities. In Electrophoresis, Vol. 2 (M. Bier, Ed.), Academic Press, New York 1967. (Graduate and undergraduate levels. The above three articles, by three of the pioneers in colloid science, are some of the classical references on electrophoresis.)... 

PSA was discovered by Kara and colleagues in 1971. They called this seminal plasma protein y-seminoprotein. Li and BeUng isolated the same protein from seminal plasma and called it protem El because it has a slow (3-mobility in electrophoresis and a molecular weight (MW) of 31,000. In... 

From the above discussion, it can be concluded that both the effective charge and the hydro-dynamic radius play a major role in the control of the electrophoretic mobility in the separation of proteins by CZE. Since proteins are flexible molecules, the interplay of both factors has to be taken into consideration to explain their mobility in electrophoresis. Eor glycoproteins, a full understanding of the factors that control their separation in CZE is a complex task because the size and flexibility of the glycans constitute an additional cause of structural variability. 

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. 

Electrophoresis is used primarily to analyze mixtures of peptides and proteins, rather than individual amino acids, but analogous principles apply. Because they incorporate different numbers of amino acids and because their side chains are different, two peptides will have slightly different acid-base properties and slightly different net charges at a particular pH. Thus, their mobilities in an electric field will be different, and electrophoresis can be used to separate them. The medium used to separate peptides and proteins is typically a polyacrylamide gel, leading to the term gel electrophoresis for this technique. 

Two-dimensional gel electrophoresis (2DE) is a two-dimensional technique for protein separation, which combines isoelectric focusing and sodium dodecyl sulphate (SDS) electrophoresis. The high resolving power results from separation according to charge (isoelectric point) in the first dimension and size (mobility in a porous gel) in the second dimension. Depending on the gel size, from several hundred to more than 5,000 proteins can be separated. 

It can be noted that in general this result predicts that the ratio of the dispersion coefficient to the free-solution diffusion coefficient is different from the ratio of the effective mobility to the free-solution mobility. In the case of gel electrophoresis, where it is expected that the (3 phase is impermeable (i.e., the gel fibers), the medium is isotropic, and the a phase is the space between fibers, the transport coefficients reduce to... 

Butterman, M Tietz, D Orban, L Chrambach, A, Ferguson Plots Based on Absolute Mobilities in Polyarcylamide Gel Electrophoresis Dependence of Linearity of Polymerization Conditions and Application on the Determination of Free Mobility, Electrophoresis 9, 293, 1988. Caglio, S Chiari, M Righetti, PG, Gel Polymerization in Detergents Conversion Efficiency of Methylene Blue vs. Persulfate Catalysis, as Investigated by Capillary Zone Electrophoresis, Electrophoresis 15, 209, 1994. 

Giddings, JC Boyack, JR, Effect of Stabilizing Media on Zone Mobility and Spreading in Electrophoresis, Journal of Theoretical Biology 2, 1, 1962. 

Stigter, D, Electrophoresis of Highly Charged Colloidal Cylinders in Univalent Salt Solutions. 1. Mobility in Transverse Field, Journal of Physical Chemistry 82, 1417, 1978. 

Structural Analyses of Hemoglobin Variants It has become Impossible to characterize nearly any abnormal hemoglobin by Its electrophoretic and/or chromatographic mobility only This Is most strikingly demonstrated by the fact that over fifty different variants behave similar to Hb-S In electrophoresis Characterization, therefore, often requires detailed structural analyses or the demonstration of a property unique to a specific variant Some of the techniques used In these studies will be... 

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. 

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. 

Finally, isoelectric focusing has been a useful extension of basic gel electrophoresis in protein analysis. In this technique, a series of ampholytes is placed on the slab via electrophoresis. An ampholyte is a substance whose molecule contains both acidic and basic functional groups. Solutions of different ampholytes have different pH values. Different ampholyte molecules differ in size and therefore will have varying mobilities in the electrophoresis experiment. Thus, these molecules migrate into the slab, take... 

Mobile phases in chromatography and buffer systems in electrophoresis are examples of frequently used solvent mixtures. In a mixture of p components, only p— can be varied independently, which means that maximally p— mixture-related variables can be examined in the type of experimental designs typically used in robusmess testing. The value of the pth variable is determined by those of the other and used as adjusting component to complete the mixture. If one of the mixture components has an important effect on a response, then the composition of the whole mixture is important and should be strictly controlled. ... 

While the electroosmotic flow is a positive attribute of electrophoresis in most cases, there are instances where EOF needs to be carefully controlled. For example, too high an electroosmotic flow may decrease resolution, especially of cations with similar mobility. In a different case, when analyzing anions of very different mobilities (anorganic and organic) in one run, the electroosmotic flow needs to be reversed (5). Furthermore, alternative elec-... 

Capillary zone electrophoresis is a separation technique that benefits from very high efficiency, not selectivity. This is in contrast to chromatography, for which the converse is true. Differences in mobility in the range of 0.01% can be enough for complete resolution of neighboring peaks. The resolution R is defined as... 

S Sabbah, F Suss, GKE Scriba. pH-Dependence of complexation constants and complex mobility in capillary electrophoresis separation of dipeptide enantiomers. Electrophoresis 22 3163—3170, 2001. 

Under this condition of reduced solution amounts, the amount of the SDS ions in the electrolyte solution decreases with time and protein mobility during electrophoresis becomes gradually reduced if the applied potential is maintained at a constant voltage. Applying the condition of constant current, the voltage is increased to maintain the separation mobility in the latter half of the process. 

Electrophoresis is one of many electromigrational separation techniques which include isotachophoresis, immunoelectrophoresis and isoelectric focussing that have been used to separate various species on the basis of their different mobility in an electric field. These techniques can be used not only to achieve separations but also it is possible to identify the ligand bound to the metal. This can be done by comparing the isoelectric points, immunological behaviours, extent of mobilities or step heights of the sample constituents with those of well-characterised standards. A difficulty, however, is in the determination of the metal constituent itself. Except in the case of radioisotopes, the activities of which can be easily measured, non-radioactive elements can be detected only after further separation steps. 

---