Metrohm 901 Titrando - Manual (Page 46)

4.1 Volumetric titration
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901 Titrando
4.1.6.3 Working with solid samples
If possible, solid samples are to be extracted or dissolved in a suitable sol-
vent. The resulting solution is injected, during which a blank value correc-
tion for the solvent must be carried out.
If no suitable solvent can be found for a solid sample, or if the sample
reacts with the Karl Fischer reagent, then a Karl Fischer oven should be
used.
If solid samples have to be directly added to the titration cell, they can be
inserted through the ground-joint opening. While doing so, take care to
ensure that
￭ the sample releases its moisture completely.
￭ no side reaction with the Karl Fischer reagent takes place.
￭ the surface of the electrode is not covered by the sample substance
(incomplete KF reaction!).
￭ the Pt wires of the indicator electrode do not become damaged.
4.1.7 Optimum working conditions
4.1.7.1 Drift
A constant drift in the range of ≤ 10 µL/min is all right. Lower values are,
however, quite possible. Higher but stable values will still produce good
results, because the drift can be compensated.
A constantly high drift can be caused by water-containing deposits in
inaccessible parts of the titration vessel. In these cases, shaking the titra-
tion vessel can reduce the value. Make sure that there are no drops above
the liquid level in the titration vessel.
When you work with a Karl Fischer oven, a drift ≤ of 10 µL/min is all right.
The drift depends on the gas flow (the smaller the gas flow, the lower the
drift).
4.1.7.2 Reagent replacement
The electrolyte solution must be replaced in the following cases:
￭ The titration vessel is too full.
￭ The drift is too high, and cannot be reduced by shaking the titration
vessel.
Exhausted electrolyte solution is best disposed of by aspiration. To do this,
you can use, for example, an 803 Ti Stand with built-in membrane pump.
An advantage is that the titration vessel does not have to be disassem-
bled.
In the event of severe contamination, the titration vessel can be rinsed
with a suitable solvent which is also aspirated.