where Pe is the Peclet number that characterizes the effect of
convective solvent flow and K=zF(Dy)/(RgasT), in which Dy is
the applied voltage across the membrane, F is the Faraday
constant, Rgas is the gas constant, T is the temperature, and z is
the charge number of the permeant (3). For DC iontophoresis
transport at 37-C when the applied electric field across the
membrane is 1 V, K=37. For a neutral permeant, the
enhancement factor (E$y ) becomes: