The surface chemistry of maize naturasorbent was altered in this work by the modifying agents: phosphoric acid and different amines (triethanolamine, diethylenetriamine and 1,4-diamitiobutane). Removal of methyl orange (25 mg 1(-1)) was <50% by maize corn cobs modified by phosphorylation and higher by the quaternized samples: 68% with the 1,4-diaminobutane and 73% with the diethylenetriamine modificators. Adsorption of arsenite by the samples modified with phosphoric acid/ammonia was 11 mu g g(-1), which corresponds to 98% removal from a 550 mu g As 1(-1) solution for an adsorbent dose of 50 mg ml(-1). The samples modified by phosphoric acid/urea removed 0.4 mu g g(-1) arsenate from a 300 mu g As 1(-1) solution. Adsorption of methyl orange, arsenite and arsenate was superior by the chemically modified maize cobs judged against the initial naturasorbent. For comparison, removal by the commercial anion exchanger was 100% for methyl orange, 45% (5 mu g g(-1)) for arsenite and 99% (5 mu g g(-1)) for arsenate. (C) 2007 Elsevier Ltd. All rights reserved.