The boundary effect oil electrophoresis is investigated by considering the electrophoresis of a spherical particle in a non-Newtonian fluid normal to a planar Surface under conditions of low surface potential and weak applied electric field. The Carreau model, which is widely used for the description of polymeric fluids of shear-thinning nature. is adopted to simulate the non-Newtonian behavior of the fluid. We show that, in general, shear thinning has the effect of raising the electrophoretic mobility of a particle. The thinner the double layer, the more significant this effect is. and, since the presence of the planar surface has the effect of enhancing the shear-thinning, effect. the closer a particle is to the planar surface, the larger is its mobility. Both the shear rate and the viscosity of the fluid vary most significantly in the gap between the particle and the planar Surface, and the maximal shear rate and the minimal Viscosity occur Oil the particle surface. (c) 2004 Elsevier Inc. All rights reserved.