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Table 1 Overview of the Winkler test reactions which allow the quantification of dissolved oxygen.

From: A novel screening protocol for the isolation of hydrogen producing Chlamydomonas reinhardtiistrains

 

Reaction

Comment

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

4) Titration

I2 + 2S2O32- → 2I- + S4O62-

The oxygen concentration in each well can be determined by titrating with sodium thiosulfate

  1. 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.