Some aspects of the winkler determination of oxygen in water

The reactions in the Winkler determination of oxygen have been examined with a rotating platinum electrode and a recording polarograph. In this manner the extent of the reaction has been determined over the pH range 7-10; at a pH of 7 only about 5% of the dissolved oxygen reacts; at a pH of 9 or above the reaction is essentially quantitative. The reaction of dissolved oxygen with manganese(II) is quite rapid. The sluggish response of the polarograph recorder prevented an accurate determination of the rate, but the reaction half-times were about 2 sec or less over the pH range used.