Migration in an electric field,

Anions and cations exist in water. They migrate in an electric field and thus carry a current. Ohm s Law is applicable ... 

At the pH = Jt there is a balance of charge and there is no migration in an electric field. This is referred to as the isoelectric point and is determined by the relative dissociation constants of the acidic and basic side groups and does not necessarily correspond to neutrality on the pH scale. The isoelectric point for casein is about pH = 4.6 and at this point colloidal stability is at a minimum. This fact is utilised in the acid coagulation techniques for separating casein from skimmed milk. 

Electrolyte—chemical constituent, usually a liquid, containing ions that migrate in an electric field. 

The explicit mathematical treatment for such stationary-state situations at certain ion-selective membranes was performed by Iljuschenko and Mirkin 106). As the publication is in Russian and in a not widely distributed journal, their work will be cited in the appendix. The authors obtain an equation (s. (34) on page 28) similar to the one developed by Eisenman et al. 6) for glass membranes using the three-segment potential approach. However, the mobilities used in the stationary-state treatment are those which describe the ion migration in an electric field through a diffusion layer at the phase boundary. A diffusion process through the entire membrane with constant ion mobilities does not have to be assumed. The non-Nernstian behavior of extremely thin layers (i.e., ISFET) can therefore also be described, as well as the role of an electron transfer at solid-state membranes. 

From Example 23.8 or Figure 23.7, it is dear that the zwitterion of glycine is the principal spedes over a wide pH range, certainly from pH 3 to pH 9. The maximum concentration of zwitterion occurs at about pH 6 this is referred to as the isoelectric point of glycine. At this pH, glydne does not migrate in an electric field, since the zwitterion is a neutral species. At... 

The most important driving forces for the motion of ionic defects and electrons in solids are the migration in an electric field and the diffusion under the influence of a chemical potential gradient. Other forces, such as magnetic fields and temperature gradients, are commonly much less important in battery-type applications. It is assumed that the fluxes under the influence of an electric field and a concentration gradient are linearly superimposed, which... 

It is important to realize that the migration in an electric field depends on the magnitude of the concentration of the charged species, whereas the diffusion process depends only on the concentration gradient, but not on the concentration itself. Accordingly, the mobility rather than the concentration of electrons and holes has to be small in practically useful solid electrolytes. This has been confirmed for several compounds which have been investigated in this regard so far [13]. 

OS 93] [R 31] [P 73] Using a simplified modeling approach, it was shown that axial dispersion changes the direction and shape of moving reaction fronts and also affects the interplay between dispersion and migration in an electrical field [145]. 

An important quantity characterizing the amino acids, peptides and proteins is the isoelectric point, which is the value of pH at which the ampholytes do not migrate in an electrical field. This occurs when... 

The possible formation of a dipole is a feature of covalent bonding but it is obvious that an ionic bond results in a definite unequal distribution of electrons within a molecule and such molecules (or ions) are extremely polar. However, the fact that they carry a definite charge enables additional separation techniques to be applied. The rate of migration in an electric field (electrophoresis) and the affinity for ions of opposite charge (ion-exchange chromatography) are extremely valuable techniques in the separation of ionic species. 

The iso-electrlc point (pi) of an amino acid is the pH at which it wilt show no migration in an electric field. 

Ionic micelles will migrate in an electric field, and the ion atmosphere of the colloidal particle is dragged along with it. Interpretation of micellar mobility (conductivity experiments) must take this into account. The same is true, however, of the mobility of simple ions, but the situation is more involved here since the micelle and the ion atmosphere have comparable dimensions. We see in Chapter 12 how particle and double-layer dimensions affect the interpretation of mobility experiments. 

Next, let us consider the application of Equation (21) to a particle migrating in an electric field. We recall from Chapter 4 that the layer of liquid immediately adjacent to a particle moves with the same velocity as the surface that is, whatever the relative velocity between the particle and the fluid may be some distance from the surface, it is zero at the surface. What is not clear is the actual distance from the surface at which the relative motion sets in between the immobilized layer and the mobile fluid. This boundary is known as the surface of shear. Although the precise location of the surface of shear is not known, it is presumably within a couple of molecular diameters of the actual particle surface for smooth particles. Ideas about adsorption from solution (e.g., Section 7.7) in general and about the Stern layer (Section 11.8) in particular give a molecular interpretation to the stationary layer and lend plausibility to the statement about its thickness. What is most important here is the realization that the surface of shear occurs well within the double layer, probably at a location roughly equivalent to the Stern surface. Rather than identify the Stern surface as the surface of shear, we define the potential at the surface of shear to be the zeta potential f. It is probably fairly close to the... 

Arachidic acid sols were studied with different concentrations of La3+ added. The stability ratio W and the direction of particle migration in an electric field (i.e., particle charge) were observed and the following results obtained ... 

T 0 is the solvent viscosity, II is the electrophoretic mobility, small for macroions relative to microions, and (j is the applied electromotive force across x. Neutral polysaccharides do not migrate in an electrical field, except as a moiety of an ionic complex or when they adsorb ions. Electrophoresis is a useful method for studying heterogeneity (Aspinall and Cottrell, 1970). 

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... 

Proteins are polyelectrolytes they carry positive and negative charges, and this property is ascribed to their polar amino acid side chains. Thus, proteins can be titrated, and the number of acidic and basic residues present can thereby be estimated. In addition, proteins migrate in an electrical field, and this movement is termed electrophoresis. Such migration, of course, depends on the net charge of the protein at the time of electrophoresis, which in turn depends on the pH of the medium. 

Since at present there appears to be no other method of measuring the potential, than the measurement of the velocity of migration in an electric field and the application of one or other of the formulae (28) to (28.2), we have not yet the power of verifying these formulae by experiment. 

Some of the proteins are involved in the transport of substances across the membrane, and some other proteins are enzymes that catalyze biochemical reactions. Proteins on the exterior surface can function as receptors and bind external ligands such as hormones and growth factors. Proteins migrate in an electric field positively charged proteins... 

Proteins migrate in an electric field as a function of their charge... 

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