Metrohm 751 GPD Titrino - Manual (Page 45)

2.6. Parameters, key <PARAM>
751 GPD Titrino
42
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 considered.
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
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.
• With problematical 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.