What technique is used to measure the dissolved oxygen (DO) in water?

The Winkler titration method is a widely recognized and precise technique for measuring dissolved oxygen (DO) levels in water. This method is based on the principle of redox reactions, where oxygen in the water reacts with specific reagents, typically manganese sulfate, sulfuric acid, and sodium thiosulfate.

In the process, the sample is first treated with manganese sulfate, which precipitates manganese oxide in the presence of dissolved oxygen. This precipitate is then converted into a soluble manganese compound by adding sulfuric acid. Following this, a titration using a sodium thiosulfate solution is conducted to determine the concentration of the dissolved oxygen. The amount of titrant used correlates directly to the amount of dissolved oxygen in the sample, allowing for an accurate measurement.

This method is particularly favored for its accuracy and reliability, making it a standard procedure in water quality analysis. Other techniques, like colorimetric methods, may also be used for measuring dissolved oxygen but are generally seen as less precise compared to Winkler titration, especially in low concentration ranges. Techniques like gravity sedimentation and filtration are not applicable for measuring dissolved oxygen, as they pertain to sediment or particulate analysis rather than the quantification of gas dissolved in liquids.