ABSTRACT
Oxygen cannot be determined directly by chemical methods. The Winkler procedure is an indirect method which is dependent upon the fact that dissolved oxygen oxidizes manganese ions (Mn2+) to a tetravalent state (Mn4+) under alkaline conditions. This more reactive state of manganese is capable of oxidizing iodine ions to free iodine under acid conditions. The amount of free iodine released is equivalent to the amount of oxygen originally in the sample. The iodine is then measured by reaction with standardized sodium thiosulfate prepared in a concentration such that 1 ml sodium thiosulfate = 1 mg/1 DO.
