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4
Analysis methods
4.1
Procedural instructions
when using liquid reagents
Consider error propagation based
on the possible tolerances of the
individual methods when calcu‐
lating non-directly determinable
parameters from individual meas‐
ured values.
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. Make sure that
the glass equipment does not
cause chlorine loss to rule out
these measuring errors. There‐
fore store the cuvettes for an
hour in a sodium hypochlorite
solution (0.1 g/l) and then thor‐
oughly rinse with deionised
water.
2.
Use a separate set of cuvettes
for the individual determination
of free chlorine and total
chlorine (see EN ISO 7393-2,
section. 5.3).
Label the lid and base of the
cuvette set so that there can
be no inadvertent confusion
of the cuvettes.
3.
When preparing water samples,
avoid the outgassing of chlorine
dioxide/ozone, e.g. by pipetting
and shaking. This applies partic‐
ularly for the dissolved gases
chlorine dioxide and ozone,
especially at temperatures of >
30°C. Immediately perform the
analysis after taking the water
sample.
4.
DPD colour development takes
place at a pH value of 6.2 to
6.5. Therefore the reagents con‐
tain a buffer for pH value adjust‐
ment. Ensure that strongly alka‐
line or acidic water samples are
within a pH range of 6 to 7
(using 0.5 mol/l sulphuric acid or
1 mol/l sodium hydroxide solu‐
tion).
5.
Concentrations above
4 mg/l chlorine when using
n
liquid reagents
7.6 mg/l chlorine dioxide
n
when using liquid reagents
Analysis methods
17
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