Abstract: A method of measuring oxidant in an aqueous composition using an electrode system comprising a membrane permeable to a species to be measured, a cathode situated behind the membrane, and an electrolyte between the membrane and cathode. Embodiments of the method may include contacting the membrane and an anode with the aqueous composition, and measuring the current between the cathode and anode in response to a first voltage applied between them. A pulse of a second voltage may be applied between the cathode and the anode, where the second voltage is different from the first voltage. Apparatus and computer program products which may perform the method, are also provided.