The method describes how to determine the free and total chlorine content using a titrimetric method with DPD.
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
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Free chlorine: |
Chlorine present as hypochlorous acid, hypochlorite ions or as dissolved elemental chlorine. |
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Bound chlorine: |
Percentage of total chlorine present in the form of chloramines and organic chloramines. |
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Total chlorine: |
Chlorine present as "free chlorine" and "bound chlorine". |
The analysis involves a reaction with N,N-diethyl-1,4-phenylenediamine (DPD), which forms a compound possessing a red color at a pH of 6.2–6.5. The solution is titrated with an ammonium iron(II) sulfate standard solution until the red color disappears. Total chlorine is measured through the addition of potassium iodide, of which a known amount in excess of that required is added to the solution in advance.