The observed rate of migration
of a component ()
divided by electric field strength ()
in a given medium.
Mobilities are sometimes expressed with a negative sign, because migration of the solutes or particles generally occurs in the direction opposite to the electrophoretic field (which is taken as reference for that direction).
In a solid support medium, only apparent values can be determined.
PAC, 1994, 66, 891
(Quantities and units for electrophoresis in the clinical laboratory (IUPAC Recommendations 1994))
on page 894