Development of Karl Fischer Reagents

1. Metals and Simple Substances
Key Points
Chapter II: Applications - 1
Since these substances are solids and cannot be dissolved in
methanol, they are normally measured using the moisture vaporization
method. The sample is powdered in preparation for the measurement.
During this preliminary process it is important to prevent absorption of
humidity or dissipation of the moisture content.
For volumetric titration, it is possible to disperse the sample in
dehydrated solvent and carry out Karl Fischer titration directly.
However, the moisture vaporization method is normally used.
With coulometric titration the presence of insoluble substances, such as
powdered metal, interferes with the electrode reaction. Other causes of
interference include membrane blockage. For these reasons,
coulometric titration cannot be used directly.
In most cases the moisture vaporization method is effective with these
samples. Because moisture content is commonly low, Karl Fischer
titration is carried out using the coulometric method. The heating
temperature for moisture vaporization is 100-250 � C. If necessary, the
process can be carried out at temperatures of 600-700 � C.
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