W hen a solution of charged particles is subject to an electric field, the force on a charged particle due to the electric field is (z is the number of charges on the particle; e is the charge on the electron; E is the electric field intensity; k is Boltzmann’s constant; T is the temperature; D is the diffusion coefficient; C is the concentration; T is the Faraday; $\psi$ is the potential; R is the gas constant)