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Ionic mobility, defined

The concepts of ionic mobility ui, m /s-V) and effective ionic mobility ( f, m /s-V) are introduced as representative parameters of electromigration (ionic migration). The effective ionic mobility defines the velocity of the ionic species under the effect of a unit electric field, which can be theoretically estimated using the Nemst-Townsend-Einstein relation (Holmes, 1962). Ionic mobility is related to the ionic valence (z,) and molecular diffusion coefficient (Z) m /s) of species as follows ... [Pg.288]

Figure . The ionic mobility [defined in Eq. (3)] vs. molecular weight for the iontophoretic delivery of peptides through human skin. The data obtained in the present study (j are compared with data from Yoshida and Roberts (1992)(B) and Green et al. (1991) (A). Figure . The ionic mobility [defined in Eq. (3)] vs. molecular weight for the iontophoretic delivery of peptides through human skin. The data obtained in the present study (j are compared with data from Yoshida and Roberts (1992)(B) and Green et al. (1991) (A).
Ionic mobility Defined similarly to the mobility of nonelectroly-tic particles, viz., as the speed that the ion obtains in a given solvent when influenced by unit power. [Pg.161]

The ionic mobility, defined as the average velocity per unit electrical field strength, is determined from (77)... [Pg.439]

The temperature coefficients of electrical conductivity (Tables 6-9 have well-defined maxima in the region of 30-50 mole % of sulphuric acid, which arise primarily from the shift of the equilibria in the liquid phase with temperature, but also from changes in ionic mobilities. [Pg.541]

Application of a potential between reservoirs 1 (sample) and 4 (injection waste) electrokinetically pumps sample solution as indicated in Fig. 3. In this way, a geometrically defined 150 pm (90 pi) section of the separation channel can be filled [19]. If the injection potential is applied long enough to ensure that even the slowest sample component has completely filled the injection volume, a representative aliquot of sample can be analyzed (so-called volume defined injection). This is in contrast to electrokinetic sample injection in conventional capillaries, which is known to bias the sample according to the respective ionic mobilities [61]. These characteristic differences are shown schematically in Fig. 4. It should be noted that this picoliter sample injector is exclusively controlled by the application of electric fields and does not require any active elements with moving parts such as valves and external pumps. The reproducibility of the peak height of the injected sample plugs has been reported to be within 2 % RSD (relative standard deviation) and less [19,23]. [Pg.64]

Ionic mobility — Quantity defined by the velocity of an ion moving in a unit electric field (SI unit m2 V-1 s-1). The ionic mobility of ion i (uf) is related to its molar ionic conductivity (A ) by A = zfFui, where Z is the charge number of the ion. The ionic mobility is also related to the -> diffusion coefficient (A) by the Nernst-Einstein... [Pg.370]

Molar ionic conductivity — This quantity, first introduced by -> Kohlrausch, is defined by A = Zi Fui (SI unit Sm2 mol-1), where Zj and 14 are the charge number and -> ionic mobility of an ion, respectively. The molar -> conductivity of an electrolyte M +X (denoted by A) is given by A = u+X+ + i/ A, where A+ and A are the molar ionic conductivities of the cation and anion. The A value of an ion at infinite dilution (denoted by A°°) is specific to the ion. For alkali metal ions and halide ions, their A values in water decrease in the orders K+ > Na+ > Li+ and Br- > Cl- > F-. These orders are in conflict with those expected from the crystal ionic radii, because the smaller ions are more highly hydrated, so that the -> hydrated ions become larger and thus less mobile. Based on Stokes law, the radius of a hydrated ion... [Pg.431]

The quantity lOOOac is the concentration of A ions (and also of B ions) in mol m 9 = N e is the Faraday constant (96485.31 C equiv ), and C/, is the ionic mobility of charged species i. Note that the mobility is defined as the migration speed of an ion under the influence of unit potential gradient and hence has the units m s V. It is now convenient to define a new quantity, the equivalent conductance A, by... [Pg.236]

Defined as the reciprocal of resistance (siemens, ft-1) conductance is a measure of ionic mobility in solution when the ions are subjected to a potential gradient. The equivalent conductance A of an ion is defined as the conductance of a solution of unspecified volume containing one gram-equivalent and measured between electrodes I cm apart. Due to interionic effects, A is concentration dependent, and the value, A0, at infinite dilution is used for comparison purposes. The magnitude of A0 is determined by the charge, size and degree of hydration of the ion values for a number of cations and anions at 298.15K are given in table 6.6. It should be noted that HjO and... [Pg.262]

Table 10.1 lists several equations that apply to CE. Equation 1 states that the velocity (cm/s) with which an ion moves through the capillary is a function of its mobility and field strength. Field strength (V/cm) is defined in Eq. 2. Ionic mobility (cm /V s) is defined in terms of column length, migration time and applied voltage in Eq. 3. Equation 4 states that ionic mobility (cmW s) is made up of electrophoretic and elec-troosmotic mobility. In CE as in chromatography the separation power is often stated by the plate number, N (also called the number of theoretical plates). [Pg.204]

Electrical transients (12) can also be used to evaluate particle mobilities in special circumstances. Charged particles, their counterions and other excess ions present in the suspending fluid contribute to the electrical current. When the concentration of excess ions is very low compared to the concentration of counterions, it is sometimes possible to determine the current contributed by particles versus that contributed by ions. Ionic concentrations define the extent of double layers in colloids. Transient and AC conductivities can be related most directly to the ionic concentrations and mobilities. But, again, the measurements in low conductivity fluids have to be performed in planar cells with narrow electrode spacings in order to ensure well defined electric fields. [Pg.284]

The hydration number (Nw) of an ion is defined as the number of water molecules that have lost their translational degrees of freedom because of their association with the ion. Smaller ions bind more water than larger ions and cations somewhat more water than anions. For example mean hydration number of Li+ is 4, Na+ is 3, Rb+ is 1, F— is 3, Cl- is 2,1- is 0.7. Many important physiological mechanisms are based on the hydration of ions and the consequent effects on ionic mobilities. [Pg.293]

The transport number has been defined in Section 9.1 as the fraction of the total current carried by a given ion. This is the definition most useful to the determination of transport numbers from emfs. In Chapter 11 the transport number is defined in terms of ionic mobilities, and/or individual molar ionic conductances (see Section 11.17), which are more directly linked to the methods described in that chapter. [Pg.343]

The movement of ions toward the oppositely charged electrode is called electromigration, which is quantified by the effective ionic mobility. The effective ionic mobility (f/f) is defined as the velocity of ion within the pore space under the influence of a unit electrical potential gradient. The Nernst-Einstein equation is used to relate the ionic mobility to the diffusion coefficient of the ion in a dilute solution (Koryta, 1982) as follows ... [Pg.568]

The movement of charged particles (ions) in an electric field is called electrophoresis. The basic theory of electrophoresis is related to ionic mobility u, which is also called electrophoretic mobility. When an ion in solution is moving in the direction of a field E, its velocity v depends on three factors the charge z carried by the ion, the frictional coefficient / arising from the resistance of the solution, and the strength of the field E. The quantity E is defined as... [Pg.300]

In addition, the intrinsic diffusivity of a species i is related to the ionic mobility. This relationship is given in Chapter 4 as the Nemst-Einstein equation defined by... [Pg.323]

Internal resistance R, is defined as the opposition or resistance to the flow of an electric current within a cell or battery, i.e. the sum of the ionic and electronic resistances of the cell components. Electronic resistance includes the resistance of the materials of construction metal covers, carbon rods, conductive cathode components, and so on. Ionic resistance encompasses factors resulting from the movement of ions within the cell. These include electrolyte conductivity, ionic mobility, electrode porosity, electrode surface area, secondary reactions, etc. These fall into the category of factors that affect the ionic resistance. These factors are encompassed by the term polarization. Other considerations include battery size and construction as well as temperature, age and depth of discharge. [Pg.212]

The equivalent conductance of a solution is a convenient chemical quantity. It is defined as the hypothetical conductance of one chemical equivalent of a dissolved substance A = a iV ixe, where a is the fraction of the dissolved substance (solute) in the ionic form, and iV , A, and e are, respectively, Avogadro s number, the ionic mobility, and the elementary charge. The equivalent conductance is related to the conductance a = /xe hy the relation A = 1000 a/c, where c is the solute concentration in moles per liter. With solvents of dielectric constant greater than 30, solutions of simple electrolytes generally may be expectd to be fully ionized at all concentrations, i.e., a = 1. Upon dilution of concentrated solutions in which the mobility of the ions is reduced by interionic forces, the variation of A with concentration follows the general limiting law ... [Pg.320]

Molar ionic conductivity — This quantity, first introduced by Kohlrausch, is defined by A = Zi FMi (SI unit Sm mol ), where Z and m are the charge number and ionic mobility of an ion, respectively. The molar -> conductivity of an electrolyte (denoted by... [Pg.431]


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Ionic mobilities

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