What is a recognized test method for determining dissolved oxygen?

The recognized test method for determining dissolved oxygen is the azide modification for the Winkler titration method. This method involves a series of chemical reactions where a sample of water is treated with specific reagents that react with dissolved oxygen. The resulting product is then titrated, allowing for the quantification of the amount of oxygen present in the sample.

The Winkler method is widely accepted because it provides accurate results and is a standard method used in many laboratories and environmental studies. The azide modification improves the original Winkler method by preventing interference from certain substances and enhancing the accuracy of the dissolved oxygen readings.

Other methods like direct read photometry can also measure dissolved oxygen, but they are not as universally recognized or standardized as the Winkler method. Similarly, pH differential analysis and conductivity methods do not directly measure dissolved oxygen levels; instead, they assess other water quality parameters that are unrelated to the amount of oxygen dissolved in the water.