The method describes how to determine the free chlorine and total chlorine content using a photometric method with DPD.
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 color is measured photometrically at 510 nm. 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.
The method describes how to determine the amount of chlorine dioxide in water with the titrimetric method.
Water intended for use as an ingredient in the production of beer (brewing liquor) or other foods
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. In this reaction, chlorine dioxide is reduced to a single chlorite ion. The solution is titrated with an ammonium iron(II) sulfate solution until the red color disappears. The chlorine dioxide concentration in the water sample is calculated on the basis of the quantity of ammonium iron(II) sulfate solution consumed in the titration. The formation of the red color due to the addition of DPD can take place in the presence of other compounds other than chlorine dioxide. The oxidation reaction can be brought about by any oxidizing agent and is dependent upon the redox potential and the concentration of the solution.