Development of a Photometric Method to Measure Molecular Oxygen in Water

Abstract

A photometric method to determine molecular oxygen in water was developed. When manganese(II) is oxidized by oxygen under alkaline conditions, the presence of polyphosphate can prevent the precipitation due to a coacervate reaction. The oxidized manganese later dissolves in acid to form a pink Mn(III) species, which has a stable UV/vis spectrum. The monitoring of the oxygen concentration based on the absorbance of the pink Mn(III) species at 517 nm showed a strong correlation with both the Winkler method and an optical sensor. As a result, the present method can measure not only dissolved oxygen but also fine bubbles oxygen in in the water sample with high reliability (0-26 mg dm -3 , r 2 = 0.9995). During this process, no significant interference from nitrite or metal ions was observed. The accuracy of measurement was steady at high temperatures of the water samples (≤ 363 K).