The potential of separating colloidal particles through simultaneous application of a salt gradient and a pH gradient, or pH-assisted diffusiophoresis, is evaluated by considering the case of spherical polyelectrolytes (PEs) having different equilibrium dissociation constants in an aqueous solution with KCl as the background salt. The simulation results gathered reveal that the dependence of the particle velocity on pH is more sensitive than that in pH-assisted electrophoresis, where an electric field and a pH gradient are applied simultaneously. This implies that the separation efficiency of pH-assisted diffusiophoresis can be better than that of pH-assisted electrophoresis. In particular, two types of PE having different equilibrium dissociation constants can be separated effectively by applying the former by enhancing/reducing their diffusiophoretic velocities.