The aim of this work was to investigate the mechanisms behind the rejection of polyaminocarboxylic acids, especially the influence of membrane and solute properties. The rejections of five polyaminocarboxylic acids by commercially available charged nanofiltration membrane (Desal GH, Osmonics) were studied at constant ionic strength, pressure and temperature as a function of the pH. The rejections of polyaminocarboxylic acids with Desal GH spiral-wound membrane varied from 10 to 99% at pH ranging from 1 to 7. Findings of this study indicated that the rejection of polyaminocarboxylic acids was primarily driven by Dorman exclusion and correlated with the net charge of the solute which could be calculated using protonation constants. The effects of molecular weight and molecular parameters on rejection were studied when polyaminocarboxylic acids had a net charge close to zero. (c) 2005 Elsevier B.V. All rights reserved.