YSI 900 Chlorine Colorimeter - Manual (Page 9)

9
ENGLISH
notes:
1. Vial cleaning:
As many household cleaners (e.g. dishwasher detergent) contain reducing substances, the
subsequent determination of Chlorine 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 deionized water.
2. For individual testing of free and total Chlorine, the use of different sets of glassware is
recommended (EN ISO 7393-2, 5.3)
3. preparing the sample:
When preparing the sample, the lost of Chlorine, e.g. by pipetting or shaking, must be avoided.
The analysis must take place immediately after taking the sample.
4. The DPD color development is carried out at a pH value of 6.2 to 6.5. The reagents therefore
contain a buffer for the pH adjustment.
Strong alkaline or acidic water samples must be adjusted between pH 6 and pH 7 before the
reagent is added (use 0.5 mol/l Sulfuric acid resp. 1 mol/l Sodium hydroxide).
5. exceeding the measuring range:
Concentrations above 10 mg/l Chlorine can lead to results showing 0 mg/l. In this case, the water
sample must be diluted with water free of Chlorine and the measurement repeated.
6. turbidity (can lead to errors):
The use of the DPD No. 1 tablet in samples with high Calcium ion contents* and/or high
conductivity* can lead to turbidity of the sample and therefore incorrect measurements. In this
case, the reagent tablet DPD No. 1 High Calcium should be used as an alternative. Even if
turbidity does occur after the DPD No. 3 tablet has been added, this can be prevented by using
the DPD No. 1 HIGH CALCIUM tablet.
* it is not possible to give exact values, because the development of turbidity depends on the
nature of the sample.
7. Oxidizing agents such as Bromine, Ozone etc. interfere as they react in the same way as
Chlorine.