ProMinent DULCOTEST DT1B Operating Manual page 30

Analysis methods
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 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
10 mg/l chlorine when using
n
tablets
22 mg/l bromine when using
n
tablets
19 mg/l chlorine dioxide
n
when using tablets
6 mg/l ozone when using
n
tablets
30
ð may lead to results within
the measuring range down
to 0 mg/l. In this case, you
must dilute the water
sample with water free from
oxidizing agent and repeat
the measurement (plausi‐
bility test).
6. Turbidity (causes incorrect
measurements): For water sam‐
ples with High Calcium content*
and/or high conductivity when
[DPD no. 1 tablet] the
using the
result can be the rendering
turbid of the water sample and
consequently incorrect meas‐
urements. In this case, you
must you must use the alterna‐
tive reagent tablet
[DPD no. 1 High Calcium] . If the
turbidity only appears after the
addition of the
tablet, you can prevent this by
use of the
[DPD no. 1 High Calcium] and
[DPD no. 3 High Calcium]
the
tablet. The
[DPD No. 1 High Calcium] tablet
should only be used in conjunc‐
tion with the
[DPD No. 3 High Calcium] .
ð *exact values cannot be
specified, as the formation
of turbidity depends on the
type and composition of the
water sample.
7. The DPD method used
responds to many oxidising
media, hence you must ensure
that the selected oxidising agent
is present on its own. Mixtures,
[DPD No. 3]