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Overview of the Winkler test reactions which allow the quantification of dissolved oxygen. |
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| Reaction |
Comment |
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| 1) oxygen fixation |
Mn2+ + 2OH- → Mn(OH)2 4Mn(OH)2 + O2 + 2H2O → 4Mn(OH)3 (s) |
Dissolved oxygen is fixed with manganese chloride |
| 2) Manganese dissolving |
2Mn(OH)3 + 2I- + 6 H+ → 2Mn2+ + I2 + 6H2O |
Acidifying the solution by adding H3PO4 dissolves the brown precipitate. Mn(III) cations are liberated which oxidize added iodide to iodine |
| 3) Starch addition |
Elementary iodine intercalates within starch helices turning the solution into a dark-blue color |
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| 4) Titration |
I2 + 2S2O32- → 2I- + S4O62- |
The oxygen concentration in each well can be determined by titrating with sodium thiosulfate |
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The test comprises four steps in which MnCl2, KI/NaOH, H3PO4 and starch solutions are added successively into the test wells. Cultures which stay anaerobic can be determined colorimetrically. | ||
Rühle et al. BMC Plant Biology 2008 8:107 doi:10.1186/1471-2229-8-107 |
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