Migration velocity of ion

The migration velocity of ions appears relatively small at first glance. For example, in the case of a voltage drop of 1 V and a 1 cm thick layer of solution and therefore a field of 100 V m , it will be between 10 and 10 m s. Even so, in 1 s, the ion will cover a distance of almost 10,000 times its diameter. 

In the solution of an electrolyte, the intrinsic migration velocities of ions (see equations (6.3.8c, e) and Table 6.3.1) are, in general, different. Thus, the velocity of the cation is different from that of the anion, f n the absence of any external electric field, these differential migration velocities create a potential gradient, the diffusion potential, which reduces the speed of the faster ion and increases the speed of the slower ion. Ultimately, the rate of diffusion of each ionic species is equal to that of the binary electrolyte. The diffusion coefficient D of a binary electrolyte, e.g. in a dilute solution, given by (Newman, 1973, 1991)... 

It is known that the migration velocity of ions in water is about 5 times that of in water. Therefore the ions will migrate about 5 times faster into the KCl solution (per unit time this means 5 times the number) than the K " ions into the HCl solution (Fig. 16). In our example the Cl" concentration is the same in both solutions, so no net... 

When an electric field is applied, jumps of the ions in the direction of the field are somewhat preferred over those in other directions. This leads to migration. It should be noted that the absolute effect of the field on the ionic motion is small but constant. For example, an external field of 1 V m-1 in water leads to ionic motion with a velocity of the order of 50 nm s 1, while the instantaneous velocity of ions as a result of thermal motion is of the order of 100 ms-1. 

If solutions of two electrolytes are brought into contact there is, generally speaking, a potential difference between them, just as there is one at the interface mercury-electrolyte in the capillary electrometer. This potential difference has been shown by Nemst to depend on the differences in the concentrations and the migration velocities of the ions. Smith uses dilute solutions containing equivalent amounts of KI and KC1 the kation is thus the same in both solutions, and the migration velocities of the I and Cl ions are nearly equal, so that, according to Nemst s theory, there should be no potential difference or double layer at the interface. These... 

Three situations may occur regarding the migration velocities of the ions in the sample zone (vs) and in the bulk electrolyte (v ), as is shown in Fig. 17.7 ... 

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... 

Example Determine the migration velocity of a conducting l-) m panicle in an electric field with an intensity of I kV/cm. The ion concentration is 10 cm and ion mobility 2(cm/sec)/(V/cm). These conditions approximate those in an electrical precipitator... 

A compound bearing an electric charge move within the electrolyte assumed to be immobile at a velocity Upp (m/s) which depends upon the conditions of the experiment and of its own electrophoretic mobility fi p. For a given ion and medium, p,pp is a constant which is characteristic of that ion. This parameter is defined from the electrophoretic migration velocity of the compound and the exerted electric field E, using expression 8.1 ... 

There are several different modes of conducting electrophoresis in capillary columns. We have just discussed at length the basic one, CZE, which is conceptually the simplest. It is conducted with a liquid buffer of uniform composition of electrolyte concentration and pH level. There are more complex versions, in which the buffer liquid is enmeshed in a porous gel of hydrophilic polymer, or the concentration or the pH of the separation buffer is not constant along the length of the column, leading to variations in the migration velocities of individual ions as the separation proceeds. Several of these will be discussed subsequently. 

The transport of ions in solution under an electric field is called migration. The velocity of ion movement is proportional to the strength of the electric field and the charge and size of the ion. A comparison of different ions is possible based on their mobility u (Table 2.2). The hydrogen and hydroxyl ions show the highest ion mobilities due to their interaction with the solvent water. 

With EOF, the overall migration mobility of ions is the resulting vector sum of the Hep and Heo-The velocity of ions is expressed as Eq. (9) ... 

S. Terabe and T. Isemura, Effect of polymer ion concentrations on migration velocities in ion-exchange electrokinetic chromatography,/. Chromatogr., 515, 667, 1990. 

Cations move from the anode toward the cathode, whereas anions move from the cathode to the anode under the influence of an electrical field. The migration velocity of an ion, v/, in a dilute solution is (77)... 

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