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8.
Measuring tolerances
when determining the
ozone content:
0 ... 0.67 mg/l: ± 0.03
–
mg/l
> 0.67 ... 1.3 mg/l:
–
± 0.07 mg/l
> 1.3 ... 2.0 mg/l:
–
± 0.13 mg/l
> 2.0 ... 2.7 mg/l:
–
± 0.20 mg/l
ð Explanatory notes, see
Ä Further information
on page 20 .
4.3
Procedure instructions when
using tablets
When calculating non-directly
determinable parameters from
individual measured values
error propagation based on the
possible tolerances of the indi‐
vidual methods must be consid‐
ered.
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. To exclude this
measurement error, the cuv‐
ettes must not contain any sub‐
stances that have a chlorine
demand. Therefore the cuvettes
must be stored in a sodium
hypochlorite solution (0.1 g/l) for
one hour and then thoroughly
rinsed with deionised water.
2.
For the relevant specification of
free chlorine and total chlorine
use a separate set of cuvettes
for each determination (see EN
ISO 7393-2, section. 5.3).
Analysis methods
29
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