Using the mobile adsorption model which was previously developed to describe the kinetics of polyelectrolyte adsorption on charged sorbents, we have determined the polyelectrolyte concentration profiles from the amount of polyelectrolyte adsorbed on the successive plates of a chromatographic column resulting from the progressive coverage of the successive plates with species of two different sizes, initially present at equal concentration. This investigation was done with stacked glass microfiber filters (stationary phase) and two fractionated samples of poly(4-vinylpyridine) differing by their molecular weight (flowing phase). Radiolabeling enabled determination of the adsorption of each polyelectrolyte fraction. Selective and fast adsorption of high molecular weight polyelectrolytes detrimental to small polyelectrolytes profoundly modified the concentration profile determined by simulation. This information makes clear some major difficulties inherent in experimental studies of polyelectrolyte adsorption on charged adsorbents.