Migration velocity field charging

Migration velocity The electrophoretic velocity of a charged particle in an electric field. 

Particle migration velocity The velocity at which a charged particle moves in a given direction in an electric field. 

The separation of charged compounds is based on the differences in migration velocity (v) when the electric field is applied. Migration velocity is derived by dividing the length of the capillary from injection to detection (1) by the measured migration time (t) ... 

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... 

Separations in CE are based on the different velocities of charged species when they encounter an electric field thus a key parameter in CE is electrophoretic mobility. Mobility (pi) is the rate of migration of sample components under a given set of conditions ... 

The separation mechanism is based on stereoselective ion-pair formation of oppositely charged cationic selector and anionic solutes, which leads to a difference of net migration velocities of the both enantiomers in the electric field. Thus, the basic cinchona alkaloid derivative is added as chiral counterion to the BGE. Under the chosen acidic conditions of the BGE, the positively charged counterion associates with the acidic chiral analytes usually with 1 1 stoichiometry to form electrically neutral ion-pairs, which do not show self-electrophoretic mobility but... 

As can be observed in Equation (11) the migration velocity is directly proportional to the ionic charge of a compound and the applied electric field strength. It is inversely proportional to the viscosity of the medium and the hydrodynamic radius of the compound. The electric field strength is determined by the applied voltage difference (V, in V) and the... 

Figure 3.38. Principle of the photorefractive effect By photoexcitation, charges are generated that have different mobilities, (a) The holographic irradiation intensity proHle. Due to the different diffusion and migration velocity of negative and positive charge carriers, a space-charge modulation is formed, (b) The charge density proHle. The space-charge modulation creates an electric Held that is phase shifted by 7t/2. (c) The electric field profile. The refractive index modulation follows the electric field by electrooptic response, (d) The refractive index profile.

A variety of microscale separation methods, performed in capillary format, employ a pool of techniqnes based on the differential migration velocities of analytes under the action of an electric field, which is referred to as capillary electromigration techniques. These separation techniques may depend on electrophoresis, the transport of charged species through a medium by an applied electric field, or may rely on electrically driven mobile phases to provide a true chromatographic separation system. Therefore, the electric field may either cause the separation mechanism or just promote the flow of a solution throughout the capillary tube, in which the separation takes place, or both. 

Figure 8.4—Influence of net charge, field, viscosity and species size on the migration velocity vector of an electrolyte assumed to he immobile. The general term cataphoresis corresponds to the displacement of ions towards the cathode whereas anaphoresis corresponds to the displacement of ions towards the anode.

In all electrophoresis experiments, a compound bearing an electrical charge will migrate under the influence of the electric field E. The migration velocity, also called the electrophoretic migration velocity v EP, depends on the electrophoretic mobility of the ion /iEP. 

To estimate the particle migration velocity, it is assumed that (1) particles are spherical and have the same size (2) all particles are charged to the same extent (3) the particle motion is governed by the Coulomb force and the Stokes drag only and (4) the direction of the applied electric field is perpendicular to the direction of the suspension flow. 

Electrophoresis refers to the separation of solutes based on their differential migration in an electric field. The velocity of charged solutes is proportional to the applied voltage. Thus, high voltage is theoretically desirable for fast and efficient separations. In practice, the use of high electric fields... 

The velocity of migration of a charged analyte in an electric held depends on its electrophoretic mobility and on the magnitude of the applied electric field. 

In electrophoresis a separation is carried out under an electric field, but the products are not permitted to migrate all the way to, and be discharged at, the electrodes. The rate of movement of a solute depends in part on its charge. The migration velocity is defined in terms of the centimeters per second of movement for a potential drop of 1 V/cm. 

We begin by initially ignoring electroosmosis, and considering only the migration of the charged analyte species in an electric field. The migration velocity, v (see Chapter 9), is related to the analyte s mobility, p, and the electric field strength, E, by Eq. 12.1 ... 

As the limiting charge on the particle is proportional to the radius squared, the migration velocity of the particle will increase with particle size. As the electric field is proportional to the applied voltage, the migration velocity is proportional to the voltage squared. 

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