Water I.D. Primelab 2.0, Manual

Page: 83 / 301

DPD 1 A and DPD 1 B reagent MUST be added to the vial BEFORE water sample is added to
avoid misreadings!
Turbidity caused by high concentration of calcium ions will affect the measurement result. To
prevent that, please use DPD HC (High Calcium) reagents.
Liquid reagents should be stored at temperatures of 5 - 10 °C in securely closed bottles.
Shake the liquid reagent thoroughly before adding the liquid to the vial.
Do not clean glassware and equipment with household detergents, as these could greatly
reduce the measurement result. To prevent any contamination, the cuvette, lid and stirrer
should be stored in a 0.1 % sodium hypochlorite solution for one hour. Then rinse with distilled
water, thoroughly.
The DPD reagent buffers the pH value of the sample water in the range of 6.2 to 6.5, which is
essential for colour development. If the sample water is very alkaline or acidic, this must be
adjusted to a pH within the range of 6 to 7 by addition of 0.5 mol/l sulphuric acid or 1 mol/l
caustic soda, respectively, before the DPD reagent is added.
Make sure no chlorine escapes while preparing the sample. The measurement must be
performed directly after sampling.
If the sample water contains further oxidizing agents, these will react like chlorine and contribute
to the measurement result.
If the sample water contains more than 20 mg/l chlorine, a measured value of 0 mg/l can be
displayed. In that case, a dilution is recommended.
T28/204 T28/204