Velocity, of ions

This reduces many of the complications arising from the need for spatial focusing. Also, the initial velocity of ions generated are invariably in the TOP direction. 

Table 3. Drift Velocities of Ions in a Field of 1 Volt/Cm Aqueous Solution...

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. 

From the frequency at the maximum growth rate that was obtained in region I, mean drift velocity of ion is calculated as v+ = 2fA =... 

Juhasz, P. Vestal, M.L. Martin, S.A. On the Initial Velocity of Ions Generated by MALDI and Its Effect on the Calibration of Delayed Extraction-TOF Mass Spectra. 

The relation between the conductance of a solution and the velocity of ions can be arived at by the following reasoning Let us consider a cell with two electrodes set exactly 1 cm apart and of sufficient areas to contain a volume q> of a solution, containing 1 gram-equivalent of the electrolyte, between them. If the potential difference between the two electrodes equals 1 V the current passing through the system equals the equivalent conductance (see equation III-ll). 

From the known values X°+ and X° the corresponding velocities of ions r°+ and v° can be finally calculated on substituting a, — 1 (valid at infinite dilution) in equations (III-19 and 111-20)... 

Table 6. Absolute velocities of ions at infinite dilutions in cin/sec. (V/cm)...

In this way we eliminate errors resulting from the application of equation (III-26), which is based on the assumption that ionic mobility is independent on the concentration of the solution. Equation (III-27) may be regarded as correct, because we compare now conductances of a partly dissociated (real) solution and of a fully dissociated (hypothetical) solution at the same ion concentration, in which case the interionic forces have the same influence upon the velocity of ions. 

Following the equation (III-25) the decrease of conductance of an electrolyte with increasing concentration is due to the lowering of the degree of dissociation on one hand and to lessening of the value of the fraction (i>+ + v )l(v + 0 — = /A on the other hand this value /A is called conductance coefficient and it expresses the effect of interionic forces upon the velocity of ions ... 

Unequal velocities of ions cause changes in concentrations in the proximity of electrodes. From these changes the transference numbers can be calculated provided the quantity of electricity passed through the electrolyte is known (Hittorf s method). 

Though the two types of mobilities are closely related, it must be stressed that the concept of absolute mobility is more general because it can be used for any force that determines the drift velocity of ions and not only the electric force used in the definition of conventional mobilities. 

Donnan dialysis combines the advantages of conventional dialysis (cheap driving force) with those of electrodialysis (charged membranes, selective transport across the membranes). It also makes use of the different mobility and different transport velocity of ions of the same or opposite charge. Donnan dialysis is now beginning to play a role in waste management. More details are available in our own reports on the utilization of sulphate and nitrate ions taken up from the post-nitrification spent liquors [16 ]. 

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