1.1 Methods
Notes:
1. Vial cleaning:
As many household cleaners (e.g. dishwasher detergent) contain reducing substances,
the subsequent determination of Chlorine dioxide may show lower results. To avoid
any measurement errors, only use glassware free of Chlorine demand.
Preparation: Put all applicable glassware into Sodium hypochlorite solution (0.1 g/l) for
one hour, then rinse all glassware thoroughly with deionised water.
2. Preparing the sample:
When preparing the sample, the lost of Chlorine dioxide, e.g. by pipetting or
shaking, must be avoided. The analysis must take place immediately after taking the
sample.
3. The DPD colour development is carried out at a pH value of 6.2 to 6.5. The reagent
tablet therefore contains a buffer for the pH adjustment.
Strong alkaline or acidic water samples must be adjusted between pH 6 and pH 7
before the tablet is added (use 0.5 mol/l Sulfuric acid resp. 1 mol/l Sodium hydroxide).
4. Exceeding the measuring range:
Concentrations above 19 mg/l Chlorine dioxide can lead to results showing 0 mg/l.
In this case, the water sample must be diluted with water free of Chlorine dioxide.
10 ml of the diluted sample should be mixed with the reagent and the measurement
repeated.
5. If ??? is displayed at a differentiated test result see page 262.
Oxidising agents such as Chlorine, Ozone etc. interfere as they react in the same way as
Chlorine dioxide.
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