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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 will be mixed with the reagent and the measurement repeated.
5. Oxidising agents such as Chlorine, Ozone etc. interfere as they react in the same way as
Chlorine dioxide.
Reagent Form of reagent/Quantity Order-No.
Set
DPD No. 1 / No. 3
Tablet / per 100
inclusive stirring rod
517711BT
DPD No. 1 Tablet / 100 511050BT
DPD No. 3 Tablet / 100 511080BT
GLYCINE Tablet / 100 512170BT
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