GOOD LABORATORY PRACTICE (KARL FISCHER METHOD)

General remarks
Performing Karl Fischer titrations is more demanding than other volumetric titrations.
Radiometer Analytical titrators guide the user step-by-step to ensure reliable and
reproducible results are obtained every time.
The main difficulties of a Karl Fischer titration are:
• The omnipresence of water in the atmosphere. Leakage of water and
vapour in the cell during the titration will lead to an erroneous result.
Radiometer Analytical has designed a titration stand which is easy to use and
ensures operation without contact with the external atmosphere. An
electronically driven pump allows addition of solvent and emptying of the cell
without any leakage. The user should inspect the desiccant tubes regularly
and replace the desiccant when saturated.
• Side reactions will be detrimental to the accuracy of the titration. For example,
the reaction with iodine (ketones and aldehydes) or reactions which inhibit
the response of the indicating electrodes. In the first case, a specific reagent
should be used to reduce the influence of these side reactions and in the
latter, an oven is required.
The KF titration cell
It is recommended to always leave the cell on stand by, i.e. the titrator measures the
effect of ambient humidity during conditioning so that the KF cell is ready for
immediate use.
The built-in electronically driven pump assures the draining of the KF cell. In this
way, exchanges with ambient humidity as well as solvent handling are avoided.
Start the pump then press the emptying button. When the cell is empty, release the
button then stop the pump. To add solvent, start the pump then hold the solvent
button down until the solvent reaches the level marked on the cell.
The KF titration cell should be completely disassembled if not being used for
longer periods of time. The parts should be washed in methanol and then dried.
The parts can also be dried in an oven. The temperature of the oven must not
exceed 50°C. Higher temperatures are not recommended as this can lead to
deformation of plastic parts.
Stirring speed
The stirring speed should be selected to ensure a rapid mixing of the reagent
added, without introducing an excessive amount of air into the solution. Insufficient
stirring can easily lead to an over-titration whereas excessive stirring may disturb
the response of the electrodes.
Delivery tip and indicating electrode
The delivery tip should be placed after the indicating electrode following the
direction of rotation of the stirrer.
The burette
Most manufacturers titrant and solvent bottles can be connected directly to
Radiometer Analytical titrators using the bottle stoppers supplied.
The burette should be equipped with an absorption chamber filled with silica gel or
a molecular sieve for H2O absorption. This will preserve the titre of the titrant and
limit titrant consumption during the pre-titration of the solvent.
GLP
Even with all the precautions taken in order to preserve the titre of the KF reagent,
it is recommended to perform a calibration at regular intervals. The titrator alerts the
operator when a calibration is necessary. The calibration interval is entered by the
operator during programming. In the same way, when using dedicated PC software,
it is possible to enter a KF titre expiry date during programming of the KF reagent
library. The operator will then be prompted when it is time to replace the KF reagent.
Use of dedicated PC software allows unlimited archiving of results and data and
lets you consult your results and methods at all times. As many as 7 titrators can be
connected via a standard RS232C serial port.
Safety
A ventilation hood is advisable, particularly if a titrant containing pyridine is used.
Please note that, almost all KF titrants and solvents used are inflammable and
toxic.