ð
can lead to results within the
measuring range down to 0
mg/l. In this case, dilute the
water sample with water
free from oxidizing agent
and repeat the measure‐
ment (plausibility test).
6.
Any turbidity that occurs during
the colour reaction leads to
exaggerated results. Prevent
this error by pre-diluting the
water sample with water free of
oxidizing agent.
7.
After use immediately close the
dropping bottles containing the
liquid reagents using the
respective screw caps in the
matching colour. Store the
reagent set at + 6°C to + 10°C.
8.
The DPD method used
responds to many oxidising
media, hence ensure that the
selected oxidising agent is
present on its own. Mixtures
e.g. of 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 designated as
chlorine.
A steady increase in the meas‐
ured value of a water sample
therefore indicates that a further
oxidising agent (e.g. bromide or
iodide) is present alongside the
selected oxidising agent (e.g.
chlorine). This oxidising agent
may bleed through into the
measurement due to certain cir‐
cumstances (many times higher
concentration, equilibria, higher
temperature). The resulting
error can be minimised by
working quickly and immediately
reading off the measurement.
ð
These interference effects
are also known to occur with
these systems {combined
chlorine ⇛ free chlorine} and
{chlorite ⇛ chlorine dioxide}.
Analysis methods
18