Macromolecular oxidant [P]-SO2NBrNa (a macroporous styrene/divinylbenzene copolymer containing N-bromosulfonamide functional groups in the sodium form) was synthesized and used to oxidize arsenites to arsenates in dilute aqueous solutions. The oxidant, containing active bromine (1.65 mmol/g) in its functional groups, was obtained through the transformation of Amberlyst 15 (Rohm and Haas) commercial cation exchanger's sulfonic functional groups. The batchwise method and the column method and NaAsO2 solutions (375, 93 and 10 mg As(III)/dm(3)) in water alone and in 0.01 M NaOH were used in the investigations. Special potentiometric, reductometric measurements showed that the investigated oxidation reaction was favoured by a weak acidic to weak alkaline medium. The determined redox potential of the resin was 440 mV at pH = 6.3 and 130 mV at pH = 11.01. In the column process experiments, conducted using NaAsO2 solutions with a concentration of 10 mg As(III)/dm(3) at a flow rate of 6 BV/h, a breakthrough (defined as the exceedance of 0.01 mg As(III)/dm(3) in the effluent) would occur after the solutions amounting to about 1700 bed volumes were passed though the column. (c) 2012 Elsevier Ltd. All rights reserved.