A generalized theoretical model for the measurement of effective diffusion coefficients of heterovalent ions in ion exchange resins by the zero-length column method was developed. The model included the resistance to mass transfer both in the particle and in the film and described ion fluxes with Nernst-Planck equations. Equilibria were described using a model based on the mass action law. The values of intraparticle diflusivity of Cu2+, Cd2+, Zn2+, and H+ on commercial Amberlite IR-120 were obtained by non-linear regression, these values agree fairly well with data reported previously in literature. The following trend was observed: Dc > DZn > D-Cd. (C) 2003 Elsevier Ltd. All rights reserved.