A Simple Spectrophotometric Method for the Determination of Dissolved Oxygen in Environmental Waters

A simple spectrophotometric method has been developed for the determination of dissolved oxygen in environmental water samples. This method is based on red-brown color development of manganese(III) dissolved from manganese(III) hydroxide, which was oxidized with dissolved oxygen from manganese(II) hydroxide precipitated in an aqueous solution ; the amount of the oxidized manganese(III) hydroxide was equivalent to that of dissolved oxygen in the solution. To a water sample, which was taken into a graduated syringe, a manganese(II) sulfate solution and a sodium hydroxide solution were added to form a manganese(III) hydroxide precipitate, and then the precipitate in the water sample was dissolved with sulfuric acid. The color intensity due to dissolved manganese(III) was proportional to the concentration of dissolved oxygen. Up to 14 mg L−1 of dissolved oxygen could be determined spectrophotometrically at 490 nm with a relative standard deviation of 1.1%. The established method was successfully applicable to environmental water, such as river and lake water samples.