Adsorption processes involving copper on chitosan or chemically modified chitosan were studied by a 2(3) factorial design. Chitosan with a degree of deacetylation determined from infrared spectroscopy was obtained from chitin by treating with 50% sodium hydroxide solution at 383 K. After reacting with succinic acid anhydride the new biopolymer presented a capacity for cation adsorption comparable to chitosan. Near constant masses of 30.0 mg of individual samples of both biopolymers were stirred for different periods of time (2 and 4 h), with 40.0 cm(3) of cation solutions at 298 +/- 1 K. The degree of adsorption was determined from aliquots of the supernatant using atomic emission spectroscopy, and the number of moles adsorbed was calculated by difference. To establish the factorial design three factors were correlated: type of chitosan, time of stirring and identity of counter anions, in order to follow the cation-biopolymer interaction process. The chemically modified chitosan presented a better interactive performance, which differs from chitosan itself. From the factorial design it was concluded that the time necessary for this system to reach the equilibrium is 2 h and a decreased scale of anion influence followed the order: CuSO4 > CuCl2 > Cu(NO3)(2). (C) 2003 Elsevier B.V. All rights reserved.22941699129136