Electrophoretic processes

Electrophoretic separation of a group of macromolecules (proteins, for example) is performed by placing a high density solution of the protein mixture on top of the gel. This solution, usually containing glycerol as the high density component, is used to prevent mixing the sample with the upper reservoir buffer which is in contact with the acrylamide gel surface. At pH 9, a commonly used pH for electrophoresis, most proteins are 

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Micellar electrokinetic chromatography is based on the effects of the interaction of the analyte with surfactant micelles on the electrophoretic process. 

A well-distributed deposition of Pt/C nanocatalyst and Nafion ionomer on bofh hydrophilic and hydrophobic carbon-based electrodes has been successfully obfained using a Pt/C concentration of 1.0 g/L, an electrical field of 300 V/cm, and a deposition time of 5 minutes [118]. The deposition of Pt/C nanocatalysts and Nafion solution via the electrophoretic process gives rise to higher deposition efficiency and a uniform distribution of catalyst and Nafion ionomer on the PEMFC electrodes. 

Louh, R. R, Huang, H., and Tsai, F. Novel deposition of Pt/C nanocatalysts and Nation solution on carbon-based electrodes via electrophoretic process for PEM fuel cells. Journal of Fuel Cell Science and Technology 2007 4 72-78. 

Since CEC is a hybrid technique, the differential migration of analytes through the stationary phase bed will generally involve lipophilic, electrostatic, and electrophoretic processes between the analytes and the stationary and mobile phases. Consequently, the applied voltage and electrical field strength and the mobile phase properties such as pH, buffer concentration, ionic strength, temperature, and the organic content will all affect the separation. For a detailed discussion, also refer to reference 10. 

Ionization changes can be efficiently corrected with the use of an isotopically labeled IS, which possesses identical ionization response and fragmentation pattem. Therefore, deuterated IS can be used to correct both the overall method variability (e.g., sample preparation, injection, electrophoretic process, etc.) as well as matrix effects since the amount of suppression from interferents is expected to be similar. However, the total concentration of analyte and IS should be below the saturation of the ionization process. Guidelines to obtain a reproducible CE—MS method were published by Ohnesorge et al. and took into account the use of an isotopically labeled IS. 

By analogy with chromatography, the record of the electrophoretic process is termed electropherograms. ... 

More complex is the separation of charged analytes in CEC, which is the result of the interplay of chromatographic and electrophoretic processes that is considered in the definition of the electrochromatographic retention factor, or overall retention factor, k introduced by Rathore and Horvath [140] ... 

In theory, if the net charge, q, on a molecule is known, it should be possible to measure / and obtain information about the hydrodynamic size and shape of that molecule by investigating its mobility in an electric field. Attempts to define /by electrophoresis have not been successful, primarily because Equation 4.3 does not adequately describe the electrophoretic process. Important factors that are not accounted for in the equation are interaction of migrating molecules with the support medium and shielding of the molecules by buffer ions. This means that electrophoresis is not useful for describing specific details about the shape of a molecule. Instead, it has been applied to the analysis of purity and size of macromolecules. Each molecule in a mixture is expected to have a unique charge and size, and its mobility in an electric field will therefore be unique. This expectation forms the basis for analysis and separation by all electrophoretic methods. The technique is especially useful for the analysis of amino acids, peptides, proteins, nucleotides, nucleic acids, and other charged molecules. 

A combination of electrochemical methods and SERS is used to detect chlorinated hydrocarbons in aqueous solutions [28], Electrochemistry prepares the surface of a copper electrode for SERS and concomitantly concentrates the analyte on the surface of the electrode, possibly by electrophoretic processes. Detection sensitivity of <1 ppm for trichloroethylene, for example, was achieved. 

The continuity equation for a single species of molecule undergoing an electrophoretic process is as follows3,70 73 ... 

Finally, when the product is formed in the system and separated from the parent compound in some eletrophoretic mode, it will be detected. Gearly, at this stage, the product has to be transported to the detector by a combination of electrokinetic and electrophoretic processes. 

It is easy to see that the electrophoretic process of Ca " uptake, if permitted to attain equilibrium against a transmembrane potential of —180 mV, would lead to either an intolerably high concentration of ionized Ca in the mitochondrial matrix, or to the extreme impoverishment of the cytosolic Ca. The latter condition is ruled out by the existence, in the cytoplasm of all cells, of numerous reactions that are obligatorily modulated by in the juM or sub-juM range. In fact, whenever direct measurements have been possible, it has been found that the concentration of free Ca in the cytosol oscillates around 0.1 juM [75-78]. 

As the mobile phase moves through the capillary containing the sorbent under the effect of this electro-osmotic flow (EOF), sample components partition between the two phases in sorption and diffusive mechanisms characteristic of liquid chromatography. Ions in the sample move both under the influence of EOF and by their added attraction toward the oppositely charged electrode (electrophoresis). Uncharged components, on the other hand, move only under the influence of EOF. Thus, sample components, in general, separate by chromatographic and, sometimes, electrophoretic processes. 

This procedure is similar in principle to Southern and Northern blots, but it is designed for the transfer of proteins from gels onto nitrocellulose membranes. An electrophoretic technique is often used to speed the transfer by 10-fold, and the apparatus used for such Western transfers is shown in Figure 9.15. The rapid electrophoretic process ensures that complete transfer occurs with minimal diffusional zone broadening. 

W. Tliormann, Large-scale electrophoretic processes, in Protein Purification, Principles, High-Resolution Methods, and Applications, J.-C. Janson, L. Riden (Eds.), Wiley-VCH, New York, 1998, pp. 651-678. 

In addition, the cations and anions are being separated by the normal electrophoretic process. Because of the high potential, this separation can be quite fast. The resolution is excellent, because the small diameter of the tube minimizes concentration broadening, diffusion broadening, and heat broadening. The absence of a gel or particles eliminates eddy migration. 

Development of a better theoretical understanding of all electrophoretic processes, IEF included, through mathematical modeling and computer simulation. Our collaborators, Drs. Saville and... 

All electrophoretic processes are essentially charge-transport processes that obey Ohm s law. In electrophoresis, this law is most conveniently expressed in terms of electrical current density, J, specific conductance, k, and electrical field strength, E. 

It should be emphasized that, within the separator, three different regions are present and each has its own regulating behaviour. The regulating functions (equations 10 and 13) are the mathematical expression of this regulating behaviour and locally they cannot be overruled by the electrophoretic process. All changes in electrophoretic parameters, e.g. concentration (conductance), pH and temperature, will be in agreement with the local regulating function. It is obvious to use these parameters for a universal detection of the zones of the various constituents. Photometric and radiometric detectors can be used for specific zone detection. 

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