Lovibond MD100 Mode D'emploi page 39

Methods
GB
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 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. Do not use the same sample vial for free and total chlorine without thoroughly rinsing
the vial betweeen the two different tests.
4. 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.
5. 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).
6. Concentrations above 8 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.
7. If chlorine is at concentrations under 2 mg/l the 0.02 – 2 mg/l measure range would be
used (CL 2).
8. Oxidising agents such as Bromine, Ozone etc. interfere as they react in the same way as
Chlorine.
MD100_3b 05/2011
39