Lovibond MiniDirect Mode D'emploi page 24

Methods
GB
Notes Chlorine:
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 contamination .
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 . 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 escape of Chlorine gases, e .g . by pipetting or shaking,
must be avoided . The analysis must take place immediately after taking the sample .
4 . The DPD colour 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 using tablets
2 mg/l Chlorine using powder packs
can lead to results showing 0 mg/l . In this event, 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 event, 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.
Oxidizing agents such as Bromine, Ozone etc . interfere as they react in the same way
as Chlorine .
24 MiniDirect_ClpH_1 09/2008