ProMinent DULCOTEST DT1B Operating Manual page 21

7.6 mg/l chlorine dioxide
n
when using liquid reagents
2.7 mg/l ozone when using
n
liquid reagents
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. Any turbidity that occurs during
the colour reaction leads to too-
high results. You can prevent
this error by pre-diluting the
sample with oxidizing agent-free
water. You must consider the
diluting ratio (e.g. 1:2) when cal‐
culating the measurement
result.
7. After use immediately close the
dropping bottles containing the
liquid reagents using the
respective screw caps of the
matching colour. Store the
reagent set at + 6 °C to + 10 °C.
8. The DPD method used
responds to many oxidising
media, hence you must ensure
that the selected oxidising agent
is present on its own. Mixtures,
e.g. from chlorine and chlorine
dioxide only yield total values.
These total values must then be
differentiated using additional
steps. To differentiate between
chlorine and chlorine dioxide,
see
[Chlorine with liquid reagent
method, section d.] . To differen‐
tiate between chlorine and
ozone, see
[Chlorine with liquid reagent
method, section e.] .
9. In water containing bromide and
iodide (primarily seawater), the
free and, as the case may be,
bound halogens formed by
chlorination are stated as
chlorine.
A steady increase in the meas‐
ured value of a water sample
therefore indicates that along‐
side the selected oxidising
agent (e.g. chlorine) a further
oxidising agent (e.g. bromide or
iodide) is present. This addi‐
tional oxidising agent (e.g. bro‐
mide or iodide) may due to cer‐
tain circumstances (many times
higher concentration, equilibria,
higher temperature) bleed
through into the measurement.
By working quickly and reading
off the measurement immedi‐
ately, the resulting error can be
minimised.
ð These interference effects
are also known to occur with
these systems {combined
chlorine ⇛ free chlorine} and
{chloride ⇛ chlorine dioxide}.
Analysis methods
21