In the electrophotographic process, electric fields are used to detach and move charged toner particles from one surface to another. In principle, electric field detachment occurs when the applied electrostatic force overcomes the toner adhesion force to a surface. For triboelectrically charged toner, many measurements indicated that the electrostatic adhesion force of toner is much greater than that calculated for a uniformly-charged-dielectric-sphere model, suggesting that the surface charge distribution on a toner particle is nonuniform. In the present work, a triboelectric charging process is discussed for understanding the mechanism that causes a dumb-bell type charge distribution on toner particles, as previously found experimentally. The electrostatic force is computed for a dumb-bell type charge distribution on an isolated toner particle by means of a recently developed computational method using Galerkin finite-element technique. The effect of the relative spacing between electrodes on the electric field detachment of charged toner particles is examined in particular. The theoretical implication of electric field detachment of toner particles of different sizes is also discussed.