Metrohm 787 KF Titrino - Manual (Page 34)

2.6. Parameters, key
787 KF Titrino
30
In the following table we attempt to show you solutions related more to the instrument's
side:
What to do if ...
Problem Possible causes and remedial action
Dosing at end too long and
increments too small. "Is never
finished!"
• Increase "min.volume incr.".
• Change stop criterion. Try to increase stop drift or
use a short stopping time as stop criterion, e.g.
• For problematic samples change solvents with
ketones or aldehydes in 2-methoxyethanol or with
amines mixture in methanol/glacial acetic, e.g., see
literature.
The increments at the end of the
titration are too large.
"Overshoots".
• Lower "max.rate". The following experiment gives you
a reference point for the optimum max.rate: Drift
display during conditioning and add sample without
starting the titration. Select a value below the
maximum drift as "max.rate".
• Optimize setup of electrode and buret tip and
improve stirring.
Solution becomes too brown at
the end of the titration.
• The methanol fraction in the solvent is too low.
Change the solvent.
• Electrode could be coated; wipe off with acetone.
Solution becomes darker with
every titration.
• Renew solvent.
• Electrode could be coated; wipe off with acetone.
The drift increases with every
titration.
• Does your sample evolve water extremely sluggishly?
Work with the KF oven.
• Are acids esterified in your sample? Change solution
more frequently. Increase buffer capacity of the
solvent.
• Does your sample contain ketones or aldehydes?
Use special reagents suitable for ketones and
aldehydes.
The endpoint is reached "too
rapidly".
• Reduce "max.rate".
The titration times become
longer and longer.
• With 2-component reagents the buffer capacity of the
solvent can be exhausted. Change solution.
• If the drift increases at the same time, see above.