Photometric Determination of Dissolved Oxygen in Water with the Reaction of Iodine and Starch

Based on the reaction between iodine and starch to give a blue colored complex with its absorption maximum at the wavelength of 574 nm,a photometric method for determination of dissolved oxygen in water was proposed.Dissolved oxygen in the sample was fixed by adding MnSO4 in an alkaline medium to form Mn2O3 from which oxygen was liberated upon addition of H2SO4,and reacted with the free I2 liberated by the reaction of KI with H2SO4.Absorbance of the blue color produced was measured photometrically at 574 nm,and content of dissolved oxygen was found from the standard curve prepared by using KIO3 standard solution as standard for dissolved oxygen.Conditions of the color reaction were studied and optimized.Beer′s law was kept in the range of 0.027-0.80 mg·L-1 of dissolved oxygen.In analyzing 3 different water samples,results obtained by this method were in consistency with the results obtained by iodometry and by the dissolved-oxygen determinator.