Winkler light-dark dissolved O2 bottle: Difference between revisions

Revision as of 07:36, 15 May 2026

Oxygen Concentration
Approach: Winkler titration (iodometric)
Context: discrete measurement
Spatial scale: mL
Temporal scale: in situ
Units: mmol O₂ L^-1
Community captured: all
Co-measurements: temperature, salinity, depth

Method Overview

Dissolved O₂ measures the gas concentrations of oxygen from the depths of interest. This measurement can be measured using the Winkler method via iodometric titration because dissolved oxygen does not directly oxidize iodide to iodine and a multi-step reaction in which manganese acts as an intermediate “transfer” agent. ^[1].

Measuring Dissolved O2 in 60 mL

Prepare Chemicals

Winkler 1 (MnCl₂) Solution
Dissolve 40 g MnCl₂·4H₂O in MQ water and make up to 100 ml in a volumetric flask. The reagent is stable for an extended period but should be stored protected from light.
KI Solution
Dissolve 15 g KI in the minimum amount of MQ water possible (warm gently if necessary).
KOH Solution
Separately, dissolve 30 g KOH in the minimum amount of MQ water possible.
Winkler 2 Solution
Combine KI and KOH solutions and fill up to 100 mL.
Sulfuric Acid 50%
Carefully add the same amount of concentrated sulfuric acid to MQ water (add only very small amounts, as the solution heats up strongly; cool in an ice bath if necessary). Do not forget the stir bar.
Sodium Thiosulfate Solution (0.01 N)
Transfer the ampoule into a 500 ml volumetric flask and fill to 500 ml with MQ water. This yields a 0.02 mol/L solution. With proper use, the titer is 1 and remains stable for about four weeks.
Starch Solution
Dissolve 1 g soluble starch in 100 ml MQ water with heating. Stable for at least 10 days if stored in a refrigerator.

Sampling

Sample for oxygen
Insert a tube to the bottom of the bottle. Let water flow slowly through until the volume has been replaced about three times (avoid air bubbles).

Remove the hose while water is still flowing.

Fix the sample
Add 600 µl Winkler 1 and 600 µl Winkler 2 (= 1/100 of the sample volume each) and sealing the winkler bottle without any bubbles. Shake the bottle vigorously for at least 30 seconds. After 30–60 minutes, a fine brown precipitate (manganese oxide) should form. The fixed samples can be stored in the dark (or wrapped in aluminum foil) at 4°C for up to 12 hours or longer.

References

↑ Winkler, L. W. (1888). *Die Bestimmung des im Wasser gelösten Sauerstoffes*. Berichte der Deutschen Chemischen Gesellschaft, 21(2), 2843–2854. https://doi.org/10.1002/cber.188802102122

[Winkler1888-1] Winkler, L. W. (1888). *Die Bestimmung des im Wasser gelösten Sauerstoffes*. Berichte der Deutschen Chemischen Gesellschaft, 21(2), 2843–2854. https://doi.org/10.1002/cber.188802102122

[1]

@@ Line 43: / Line 43: @@
 === Sampling ===
-########  Sample for oxygen by inserting a tube to the bottom of the bottle. Let water flow slowly through until the volume has been replaced about three times (avoid air bubbles).
+#'''Sample for oxygen''' <br> Insert a tube to the bottom of the bottle. Let water flow slowly through until the volume has been replaced about three times (avoid air bubbles).
 Remove the hose while water is still flowing.
+#''' Fix the sample''' <br> Add 600 µl Winkler 1 and 600 µl Winkler 2 (= 1/100 of the sample volume each) and sealing the winkler bottle without any bubbles. Shake the bottle vigorously for at least 30 seconds. After 30–60 minutes, a fine brown precipitate (manganese oxide) should form. The fixed samples can be stored in the dark (or wrapped in aluminum foil) at 4°C for up to 12 hours or longer.
-########### Fix the sample by adding 600 µl Winkler 1 and 600 µl Winkler 2 (= 1/100 of the sample volume each) and sealing the winkler bottle without any bubbles. Shake the bottle vigorously for at least 30 seconds. After 30–60 minutes, a fine brown precipitate (manganese oxide) should form. The fixed samples can be stored in the dark (or wrapped in aluminum foil) at 4°C for up to 12 hours or longer.
 == References ==