Metrohm 900 Touch Control Manual - Manual (Page 502)

31.8 Karl Fischer titration
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486 ￭￭￭￭￭￭￭￭
900 Touch Control
Problem Cause Remedy
The minimum increment is
too low. Define Titration rate = user and increase the
minimum volume increment (Min. incre-
ment) (see Chapter 29.4.2, page 323).
The stop criterion is unsuit-
able. Adjust the control parameters (see Chapter
29.4.2, page 323):
￭ Increase the stop drift.
￭ Select a short delay time.
See also: The drift becomes
greater after each titration.
The sample is over-
titrated. The increments at the end
of the titration are too
high. ￭ Define Titration rate = user and reduce
the dosing rate (Max. rate) (see Chapter
29.4.2, page 323).
The following experiment provides a clue
for the optimum dosing rate: During condi-
tioning, display the drift and add sample
without starting the titration. Select a value
below the highest drift as dosing rate.
￭ Stir faster.
The amount of methanol in
the working medium is too
low. ￭ Replace the working medium.
￭ Reduce the amount of solubility promoter,
if working with solvent mixtures, see tech-
nical literature.
The electrode may be cov-
ered. Wipe off the electrode with ethanol or a suit-
able solvent.
The solution
becomes darker
after each titration. Replace the working medium.
The electrode may be cov-
ered. Wipe off the electrode with ethanol or a suit-
able solvent.
The electrode has a short
circuit. 1. Check the Pt wires.
2. Activate the electrode check.
The endpoint is
reached too quickly. The dosing rate outside the
control range is too high. Define Titration rate = user and reduce the
dosing rate (Max. rate) (see Chapter 29.4.2,
page 323).
The titration times
with volumetric
titration are con-
stantly longer. With two-component
reagents the buffer
capacity of the solvent can
be exhausted. Replace the working medium.