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X-RAY

XENOBIOTIC

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WINKLER METHOD

Definition

A method to determine the oxygen content by titration. In the basic Winkler procedure, a sample of water is treated with manganous sulphate, potassium iodide, and sodium hydroxide. Under highly alkaline conditions, the manganous ion is oxidized by molecular oxygen to manganous dioxide, a brown precipitate. Next, sulphuric acid is added to the sample to dissolve the precipitate and produce acid conditions for the oxidation of iodide to iodine by manganous dioxide. The quantity of I2 released is proportional to the amount of O2 originally present. The amount of I2 is estimated by titration with standard sodium thiosulfate. A starch indicator is used to determine the end point of the titration.

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