Metrohm 796 Titroprocessor - Manual (Page 119)

7. Titration and measuring modes
796 Titroprocessor, Instructions for use 113 113
What to do if ...
Observation Possible causes and remedies
Final addition lasts too
long and
increments are too
small.
"Will never end!"
• Increase 'Min.increment".
• Alter switch-off criterion, e.g. try increasing the stop drift or use a shorter
switch-off time as the stop criterion.
• Change the solvent for problematic samples, e.g. for ketones or
aldehydes the use of 2-methoxyethanol or a mixture of methanol/glacial
acetic acid for amines can be recommended, see technical publications.
The increments at the
end of the titration
are too large.
"Overshoots".
• Reduce 'Max. Rate'.
An indication of the optimal Max. Rate is provided by the following
experiment: observe the drift during conditioning and add the sample
substance without starting the titration.
Select a value below the highest drift as the 'Max. Rate'.
• Optimize the arrangement of the electrode and buret tip and improve the
stirring.
At the end of the
titration the
solution is too
brown.
• The methanol content in the solvent solution is too low. Change the
solvent.
• The electrode may be coated; wipe off with acetone.
Solution becomes
darker after each
titration.
• Renew solvent.
• The electrode may be coated; wipe off with acetone.
The drift increases
after every titration.
• Does the sample only release water slowly? Use the KF oven.
• Are acids esterified in the sample? Change the solution more frequently.
Increase the buffering capacity of the solvent.
• Does the sample contain ketones or aldehydes? Use special reagents
which are suitable for ketones and aldehydes.
The endpoint is
reached "too quickly".
• Reduce Max.rate.
The titration times
become longer and
longer.
• With 2-component reagents the buffering capacity of the solvent may be
exhausted. Change the solution.
• If the drift increases at the same time please see above.