AP Lab 12: Dissolved Oxygen and
Aquatic Primary Productivity
Carolina
Purpose
• Measure dissolved oxygen in a water
sample using the Winkler Method
• Determine if temperature affects the
amount of dissolved oxygen in water
samples.
Activity A
• Label 3 BOD bottles, 4° C, 25° C, and one
30° C.
• Fill the BOD bottles with water of the
matching temperature.
– Fill the bottle by submerging it in the sample.
After the bottle fills, cap the bottle while it is
still submerged.
Winkler Method Protocol
• Step 1: Oxygen Fixation (wear gloves)
1. Uncap the BOD bottle.
2. Add 8 drops of manganous sulfate solution
to the bottle.
3. Add 8 drops of alkaline potassium iodide
azide to the bottle.
4. Cap the bottle and mix. A precipitate will
form, allow it to settle on the bottom or
shoulder.
Winkler Method Protocol
• Step 1: Oxygen Fixation continued. . .
5. Use a 1-g spoon to add 1 gram of sulfamic
acid powder to the bottle.
6. Cap the bottle and mix until all dissolves.
7. We could stop here and store at room
temperature for several days.
8. But we won’t, continue. . .
Winkler Method Protocol
• Step 2: Titration
1. Uncap BOD bottle and use it to fill the
titration sampling vial to the 20 mL line.
2. Fill the titration syringe to the top of the scale
(1.0 mL) with sodium thiosulfate.
3. Add 1 drop of sodium thiosulfate at a time to
the sample, swirling between each additional
drop, until it is a faint yellow color.
4. Remove the titration syringe and the cap
together, without disturbing the syringe. Add
8 drops of starch indicator solution.
Winkler Method Protocol
• Step 2: Titration continued. . .
5. Replace the lid of the titration tube and swirl the
sample. The solution should turn blue. (if not blue. .
. Start Over)
6. Add one drop of sodium thiosulfate at a time,
swirling until the blue color disappears. If more
sodium thiosulfate is needed, fill syringe and add
volumes together when done.
7. Read the syringe at the bottom of plunger. Each 0.1
mL of sodium thiosulfate is equal to 1.0 ppm of DO
or 1 mg DO per L of water. Record data in table 1.
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