Frans_M_Everaerts_Isotachophoresis_378342.pdf

36 CONCEPT OF MOBILITY
3.4.2. Relaxation and electrophoretic retardation
as
According to Hiickel, Debye and Onsager (see ref. I), the conductance can be written
A= '0 - Arel. - 4et. (3.28)
where A,,. and he, are corrections for the decreasing effects on the conductivity due
to the relaxation and retardation effects, respectively.
s= ___ lz+l iz- I - A: + A;
IZ+l+ lz- I 1.2- I A: + 12' I A,
Substitution of eqns. 3.29, 3.30, 3.31 and 3.32 into eqn. 3.28 gives for the molar
conductivity
A=A~-~&
with
In a similar way [ 11, for the equivalent conductance we can derive
A* = A* 0 -a* ,/ (k+I + 12- I)c*
with
(3.29)
(3.30)
(3.31)
(3.32)
(3.33)
(3.34)
(3.3 5)
(3.36)
(3.37)
In order to show the importance of the influences for different solvents and for different
charges of the ions, we calculated the effective mobilities according to these expressions
for monovalent and divalent cations in water and methanol for a hypothetical value
of the absolute mobility of 50 - lo-' cm*/V - s at a concentration of 0.01 N. The results
are shown in Table 3.1.