The retention properties of arsenic ions from an aqueous solution by water-soluble cationic polymers and cationic-anionic copolymers were investigated. Poly[(3-methacryloylamine)propyl]trimethylammonium chloride [P(ClMPTA)] and poly[(3-methacryloylamine)propyl]trimethylammonium chloride-co-acrylic acid [P(ClMPTA-co-AA] were synthesized by radical polymerization. The copolymers were prepared with feed mole ratios of ClMPTA to AA of 1 : 1, 1: 2, and 2: 1. The copolymer compositions were evaluated by FTIR spectroscopy, TG-DSC, and elemental analysis. The liquid-phase polymer-based retention (LPR) technique was used. This technique consists of retention of arsenate anions by the quaternary ammonium salt of a water-soluble polymer in a filtration membrane cell. It was shown that the polymers could bind H2AsO4- species from an aqueous solution more selectively at pHs of 6 and 8, than at a pH of 4. An increase in the polymer concentration was associated with increased retention capacity but not linearly. At the highest concentration the influence of pH was better observed. Investigation of copolymers showed the concerted action of polycations and polyanions on the ability to retain arsenic. At the lowest pH, the role of ionic strength of the media had a remarkable effect on the retention ability, independently of copolymer composition. At a pH of 6 a copolymer polycation/polyanion composition of 2: 1 had the highest selective effect. At a pH of 8, a nonequimolar copolymer composition showed the same efficiency for the retention of arsenate species. (c) 2006 Wiley Periodicals, Inc.