Frans_M_Everaerts_Isotachophoresis_378342.pdf

30 CONCEPT OF MOBILITY
Fig.3.2. Conductance cell with electrodes 1 cm apart. For further explanation, see text.
The average velocity with which an ion moves under the influence of a potential of
1 V is called the ionic mobility, and the ionic mobility at infinite dilution is called the
absolute ionic mobility. Thus,
(3.1 la)
(3.1 Ib)
(3.12)
It can be concluded from eqn. 3.12 that absolute ionic mobilities can be calculated by
dividing the equivalent ionic conductivities at infinite dilution by the Faraday constant.
The equivalent ionic conductivities can be obtained measuring the transport numbers.
As the transport numbers give the fractions of the total current carried by each ion,
ie., the fraction of the total conductance that each ion contributes, we can write
hg+ = t,'A,* (3.13a)
and
A,*- = ti A: (3.13b)
where t = transport number. Data for conductances and transport numbers in order to