High performance capillary electrophoresis - T.E.A.M.

Principles
that ion. The mobility is determined by the electric force
that the molecule experiences, balanced by its frictional
drag through the medium. That is
Electric force (F
µ e
a = E
)
(2)
Frictional force (F F
)
The electric force can be given by
F E
= q E (3)
and the frictional force (for a spherical ion) by
F F
= -6 p h r v (4)
where
q = ion charge
h = solution viscosity
r = ion radius
v = ion velocity.
During electrophoresis a steady state, defined by the
balance of these forces, is attained. At this point the forces
are equal but opposite and
q E = 6 p h r v (5)
Solving for velocity and substituting equation (5) into
equation (1) yields an equation that describes the mobility
in terms of physical parameters
q
m e
= (6)
6 p h r
From this equation it is evident that small, highly charged
species have high mobilities whereas large, minimally
charged species have low mobilities.
18