Metrohm 756 KF Coulometer - Manual (Page 111)

5.1 Troubleshooting
756/831 KF Coulometer, Instructions of Use 103
5 Error messages, troubleshooting
5.1 Troubleshooting
The determination of the free water is easily done as far as the specifications of the
reagent manufacturer regarding the "water capacity" of the reagents are concerned.
Problems may occur with specific sample matrices. The relevant literature contains many
precise analysis instructions. In the following table we attempt to show you solutions
concerned more with the instrument.
Problem Possible causes and remedies
Drift too high • Depots containing water in the titration vessel: Shake
titration vessel.
• Reagent exhausted or contaminated ⇒ exchange.
• Moisture penetrating into titration vessel:
. molecular sieve exhausted?
. septum pierced?
. seals not OK?
. ground joint sleeves not smooth?
• Generator electrode diaphragm polluted or moist.
• Sample matrix consumes iodine. Change reagent more
often.
• When working with Oven/Oven Sample Processor:
. molecular sieve of Oven/Oven Sample Processor
exhausted?
. gas flow too high?
. allow to run overnight.
. screw seals tight?
Drift unstable • Poor stirring: Stir so that mixing is efficient, but without the
formation of air bubbles.
• Reset the control parameters to standard values.
Oven parameters wrong
in Coulometer report
Switch off the report output at the oven.
Result too high • Titration vessel not properly conditioned: Shake and wait
until drift has stabilized.
• With the generator electrode without diaphragm: Set
generator current to 400 mA, see also page 33.
• Sample contains substances which can be oxidized.
• Set stop drift higher.
• Drift correction too small, e.g. with unstable drift or with
manual drift correction.