Metrohm 895 Professional PVC Thermomat - Manual (Page 40)

6.1 Problems
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32 ￭￭￭￭￭￭￭￭
895 Professional PVC Thermomat
Problem Cause Remedy
The stability time is
longer/shorter than
expected. The conductivity change is
not correctly defined. Make sure that the value defined for the con-
ductivity change in the method is correct.
See also: The stability times
are not reproducible for
multiple determinations.
See also: The induction
time is longer/shorter than
expected.
The measurement
curves are extremely
noisy. The nitrogen supply for the
measuring solution is direc-
ted to the conductivity
measuring cell. Loosen the tubing adapter on the measuring
vessel cover and turn the PTFE cannula such
that the nitrogen is no longer directed to the
electrode and fix it in this position.
Gas bubbles adhere to the
conductivity measuring cell
during measurement. ￭ Make sure that the measuring cell is clean
and free of fat. If necessary, clean thor-
oughly.
￭ In some cases, ultrapure water contains a
large proportion of dissolved air. In this
case, degas the ultrapure water before the
measurement for 5 to 10 min in a vacuum.
The curve shows a
step which means
that the induction
time is no longer
determined cor-
rectly. Side reactions occur at the
start or during the mea-
surement. These reactions
cause the conductivity in
the measuring cell to rise. ￭ Use the Evaluation suppression in the
method.
￭ In addition to Endpoint(s) activate also
Conductivity (e.g. 200 µS/cm) as stop cri-
terion in the method and select the Stop
once all the criteria have been fulfilled
option. The evaluation parameters can be
optimized on the basis of this curve, or the
curve can be evaluated manually.
￭ Increase the Evaluation sensitivity
method parameter.
The curve shows a
step at the start of
the measurement,
which has not occur-
red in previous
measurements. The reaction vessel cover
and/or the tubing still con-
tain residues from previous
measurements. These resi-
dues are then transferred
to the measuring vessel
with the flow of warm air
during a new measure-
ment. ￭ Thoroughly clean the reaction vessel cover
and the silicone tubing.
￭ Replace the reaction vessel cover and the
silicone tubing from time to time.