The amount of dissolved oxygen is a measure of the biological activity of the water masses. Phytoplankton and macroalgae present in the water mass produce oxygen by way of photosynthesis.

Dissolved Oxygen, usually abbreviated to simply 'D.O.', is widely used in water quality studies and routine operation of water reclamation facilities.

Tests, test kits, electronic and optical sensors can all be used top determine the concentration of dissolved oxygen.

How do we measure Dissolved Oxygen?

The Winkler test can be used to determine the concentration of dissolved oxygen in water samples. In this test, An excess of manganese(II) salt, iodide (I-) and hydroxide (HO-) ions are added to a water sample causing a white precipitate of Mn(OH)2 to form. This precipitate is then oxidized by the dissolved oxygen in the water sample into a brown manganese precipitate. In the next step, a strong acid (either hydrochloric acid or sulfuric acid) is added to acidify the solution. The brown precipitate then convert the iodide ion (I-) to Iodine. The amount of dissolved oxygen is directly proportional to the titration of Iodine with a thiosulfate solution.

Oxygen saturation or dissolved oxygen (DO) is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe such as an oxygen sensor or an optode in liquid media, usually water. Dissolved oxygen concentrations can also be determined by conducting a series of complex chemical reactions via a 'test kit' or by measuring electronically with an oxygen meter (a.k.a. a DO meter).

 

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