Electrophoretic mobility electric field

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

Electrophoretic Mobility The velocity with which a solute moves in response to the applied electric field is called its electrophoretic velocity, Vepi it is defined as... 

Electroosmotic Mobility When an electric field is applied to a capillary filled with an aqueous buffer, we expect the buffer s ions to migrate in response to their electrophoretic mobility. Because the solvent, H2O, is neutral, we might reasonably expect it to remain stationary. What is observed under normal conditions, however, is that the buffer solution moves toward the cathode. This phenomenon is called the electroosmotic flow. 

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). 

In the presence of a buffer with constant composition across the electrophoretic chamber, the angle of deflection (0) of the solute in the electric field is dependent upon the intrinsic electrophoretic mobility of the solute (p. ), the linear velocity of the buffer (v) and the current through the chamber (I) and can be described as [17] ... 

Trinh et al. [399] derived a number of similar expressions for mobility and diffusion coefficients in a similar unit cell. The cases considered by Trinh et al. were (1) electrophoretic transport with the same uniform electric field in the large pore and in the constriction, (2) hindered electrophoretic transport in the pore with uniform electric fields, (3) hydrodynamic flow in the pore, where the velocity in the second pore was related to the velocity in the first pore by the overall mass continuity equation, and (4) hindered hydrodynamic flow. All of these four cases were investigated with two different boundary condi-... 

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]. 

The electrophoretic mobilities of flexible macromolecnles (e.g., DNA, oligonucleotides, and other polymers) in gel media have also been extensively stndied by a nnm-ber of methods, including Monte Carlo simnlations [159,165,208,357,358,361,362,447]. In general, the mobility is expected to vary with the length of the polymer to the -1 power (p N y, however, there are complicating effects of the applied electric field as well as the... 

The velocity of migration over the applied electric field is called the electrophoretic mobility (pe) ... 

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. 

The influence of interionic fores on ion mobilities is twofold. The electrophoretic effect (occurring also in the case of the electrophoretic motion of charged colloidal particles in an electric field, cf. p. 242) is caused by the simultaneous movement of the ion in the direction of the applied... 

In the ideal case, the ionic conductivity is given by the product z,Ft/ . Because of the electrophoretic effect, the real ionic mobility differs from the ideal by A[/, and equals U° + At/,. Further, in real systems the electric field is not given by the external field E alone, but also by the relaxation field AE, and thus equals E + AE. Thus the conductivity (related to the unit external field E) is increased by the factor E + AE)/E. Consideration of both these effects leads to the following expressions for the equivalent ionic conductivity (cf. Eq. 2.4.9) ... 

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... 

Influence of the Surface Concentration of BSA. Compared to the corrected moving boundary electrophoretic mobility of BSA in solution, the mobility of BSA adsorbed onto glass is considerably faster at all ionic strengths at 1.96 pg/cm2 and somewhat faster at lower ionic strengths 1.38 pg/cm2. However, at lower adsorption densities (1.05 and 0.64 pg/cm2), the adsorbed BSA moves more slowly in the applied electric field than BSA in moving boundary electrophoresis under otherwise identical conditions, and at the lowest surface adsorption (0.64 pg/cm2) the mobility of the adsorbed BSA are even somewhat slower than in cellulose acetate gel at all conditions of ionic strength investigated. 

In order to influence a migration it is obvious that one can alter the charge of the compounds, the viscosity of the medium and the dynamic radius of the compounds. According to Eq. 17.5, the electrophoretic mobility is the proportionality factor in the linear relationship of the migration velocity and the electric field strength... 

The migration in CE is obviously influenced by both the effective and the electroosmotic mobility. Therefore, the proportionality factor in the relationship of the migration velocity and the electric field strength in such a case is called the apparent electrophoretic mobility (/iapp) and the migration velocity the apparent migration velocity (vapp). The /iapp is equal to the sum of /migration velocity is expressed as... 

The zeta potential can be measured by electrophoresis, which determines the velocity of particles in an electric field of known strength [144]. This particle velocity, v, can then be related to the electrical field strength, E, as the electrophoretic mobility, fi. This is shown by... 

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