1.1 Methods
Notes:
1. Vial cleaning:
As many household cleaners (e.g. dishwasher detergent) contain reducing substances,
the subsequent determination of Ozone 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 Ozone, 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. Turbidity (can lead to errors):
The use of the DPD No. 1 tablet in samples with high Calcium ion content* and/or high
conductivity* can lead to turbidity of the sample and therefore incorrect measurements.
* it is not possible to give exact values, because the development of turbidity depends
on the nature of the sample.
5. Exceeding the measuring range:
Concentrations above 6 mg/l Ozone can lead to results showing 0 mg/l. In this case,
the water sample must be diluted with water free of Ozone. 10 ml of the diluted
sample should be mixed with the reagent and the measurement repeated.
6. If ??? is displayed at the diffentiated test result see page 262.
Oxidising agents such as Bromine, Chlorine etc. interfere as they react in the same way as
Ozone.
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