SPECTROPHOTOMETRIC METHOD FOR THE DETERMINATION OF DISSOLVED OXYGEN IN WATER SAMPLES

A simple, rapid and sensitive spectrophotometric method is described for the determination of dissolved oxygen in tap water samples using toluidine blue as a reagent. The proposed method is based on the reaction of manganous sulphate in alkali iodide solution and liberation of iodine by manganous dioxide. The liberated iodine bleaches the blue colour of toluidine blue, and is measured at 628 nm. The decrease in absorbance is directly proportional to dissolved oxygen concentration and obeys the Beer law in the range 0.54-5.44 mu g ml(-1). The molar absorptivity, the Sandel sensitivity, detection limit and quantitation limit of the method were found to be 5.5 x 10(4) l mol(-1) cm(-1), 3.865 x 10(-3) mu g cm(2), 3.85 x 10(-3) mu g ml(-1) and 0.011 mu g ml(-1), respectively. The results of analysis of the proposed method are compared favourably with those from a reference method.