The volumetric KF titration is unusually slow

The Karl Fischer titration appears to be slow or becomes slower from time to time. What influences the KF titration speed?

Possible reasons:

The sample contains acids or bases that alter the optimal pH for the KF titration.

Recommendations:

The optimal pH range for KF titration is in the pH range 5.5 – 8. This pH range provides sufficiently high speed and a minimum of side reactions that may alter the stoichiometry. If the pH is lower, then the reaction speed is reduced, if it is above that range, side reactions become predominant. If acidic samples such as oxalic acid, acetic acid, formic acid, mineral acids, peroxides, phenols, phosphates or benzoic acid or basic samples such as aromatic or aliphatic amines, pyridines are present; ready-to-use, Imidazol-containing pH buffer solutions of the major KF reagent suppliers are available to bring the pH back into range. It is recommended to add 5 mL of pH buffer solution for 50 mL solvent solution. If testing very basic amines, a molar equivalent of salicylic or benzoic acid can be added after or before each sample titration.