Analysis Methods; Procedure Instructions When Using Liquid Reagents - ProMinent DULCOTEST DT1B Operating Manual

Analysis methods

4 Analysis methods
4.1 Procedure instructions when
using liquid reagents
When calculating non-directly
determinable parameters from
individual measured values
error propagation based on the
possible tolerances of the indi‐
vidual methods must be consid‐
ered.
1. Cleaning the cuvettes Many
domestic cleaning agents con‐
tain reducing substances. Use
of these substances leads to
false low readings when meas‐
uring chlorine/bromine/chlorine
dioxide/ozone. To exclude this
measurement error, the cuv‐
ettes must not contain any sub‐
stances that have a chlorine
demand. Therefore the cuvettes
must be stored in a sodium
hypochlorite solution (0.1 g/l) for
one hour and then thoroughly
rinsed with deionised water.
2. For the relevant specification of
free chlorine and total chlorine
use a separate set of cuvettes
for each determination (see EN
ISO 7393-2, section. 5.3).
20
Label the cuvettes set on
the top and bottom so
that inadvertent inter‐
changing of the cuvettes
is not possible.
3. When preparing water samples
you must avoid the outgassing
of chlorine/bromine/chlorine
dioxide/ozone, e.g. by pipetting
and shaking. This applies partic‐
ularly for the dissolved gases
chlorine dioxide and ozone,
especially at temperatures >
30 °C. You must carry out the
analysis immediately after
taking the water sample.
4. The DPD colour development
takes place at a pH-value of 6.2
to 6.5. Therefore the reagents
contain a buffer for pH value
adjustment. You must ensure
strongly alkaline or acidic water
samples come within a pH
range between 6 and 7 (using
0.5 mol/l sulphuric acid solution
or 1 mol/l sodium hydroxide sol‐
ution).
5. Concentrations above the
measuring range with ...
4 mg/l chlorine when using
n
liquid reagents
9 mg/l bromine when using
n
liquid reagents