How to Measure the Amount of Oxygen in Water
The content of dissolved oxygen in water is a common measure of the general health of a body of water. A higher oxygen content indicates the water can generally support more life and has less pollution. The Winkler method is the traditional means of measuring the oxygen content of water in the field and it relies on easily observable color changes in the water to make the measurements. Kits that contain the needed reagents for the Winkler test are readily available.
Things You'll Need
- 2 ml alkali-iodide-azide
- 2 ml concentrated sulfuric acid
- 2 ml manganese sulfate
- 2 ml starch solution
- 300 ml stoppered bottle
- Calibrated pipette
- Sodium thiosulfate
Instructions
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1
Fill the 300 ml bottle to capacity and use the pipette to add 2 ml of manganese sulfate below the surface of the water. Squeeze the pipette slowly so as not to produce any bubbles, thereby introducing oxygen into the sample. Add 2 ml of alkali-iodide-azide in the same manner.
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2
Stopper the bottle carefully and mix the reagents by turning the bottle upside-down a few times. Discard the sample and start over if there are any air bubbles. Allow any brownish-orange precipitate to settle to the bottom.
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3
Add the sulfuric acid below the surface of the water with the pipette. Stopper the bottle and turn it upside-down a few times to dissolve the precipitate. The sample may be stored temporarily by covering the stopper with aluminum foil and wrapping a rubber band around the foil.
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4
Add sodium thiosulfate with the pipette to 201 ml of the water sample and stir continuously until it has a pale straw color. Record the amount of sodium thiosulfate used and add 2 ml of starch solution, which should turn the sample blue.
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5
Continue adding sodium thiosulfate one drop at a time until the sample becomes clear. The sample's concentration of dissolved oxygen will be the total milliliters of sodium thiosulfate added to the sample in units of milligrams per liter (mg/L).
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