pH CONSIDERATIONS (KARL FISCHER METHOD)

The Karl Fischer reaction can only take place in a certain pH range between 5 and
7. In this pH range, the reaction remains constant. If the pH drops too low, end point
attainment becomes sluggish or an end point will not be reached at all. If the pH is
too high, side reactions occur making the titration non-stoichiometric. We can
therefore say that errors occurring during a KF titration may be due to a change in
the pH of the titration solvent.
The pH of the titration solvent can be tested using a combined pH electrode and a
pH meter. The electrode is first calibrated with aqueous buffer solutions and
afterwards the pH of the titration solvent is measured.
Note: do not place the pH electrode directly into the KF cell because excessive
moisture will be introduced along with the electrode.
For further information, consult the users manuals of the main manufacturers of
Karl Fischer reagents.