how to determine the ionic mobilities?

The ionic mobility (μ) is defined as the velocity attained by an ion moving through a gas under unit electric field.
The velocity of the ion is given by the following equation:v=E×q/fwhere:

v = velocity
f = coefficient of friction
E = electric field (Volts/cm)
q = net charge on the ion

The coefficient of friction (f) is necessary due to the factthat when the ion moves through the medium, the medium exerts a frictional force on the ion that inhibits the movement of the ion. Usually the voltage applied is held constant, so themobility (η) of the ion can be measured; it isdefined as follows:η=vEwhere:

v = velocity
E = electric field (Volts/cm)