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Analysis methods
urements. In this case, you
must use the alternative 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,
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 tablet method,
section D "Chlorine together
with chlorine dioxide"] To differ‐
entiate between chlorine and
ozone, see
[Chlorine with tablet method]
24
[DPD No. 3]
8.
In water containing bromide and
iodide, the free and, as the case
may be, bound halogens formed
by chlorination are stated as
chlorine. A steady increase in
the measured value of a water
sample therefore indicates that
alongside the selected oxidising
agent a further oxidising agent
is present. This oxidising agent
may due to certain circum‐
stances (many times higher
concentration, equilibria, higher
temperature) bleed through into
the measurement. By working
quickly and reading off the
measurement immediately, the
resulting error can be mini‐
mised.
ð These interference effects
are also known to occur with
these systems {combined
chlorine ⇛ free chlorine} and
{chlorite ⇛ chlorine dioxide}.
4.4
Quantitative determination
using tablets
Fully dissolve tablets
Make sure that the tablets have
fully dissolved before starting
measurements. Otherwise incor‐
rect measurements may result.
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