Development of Karl Fischer Reagents

2. Cereals and Dried Vegetables
Key Points
Chapter III: Applications - 2
Volumetric titration is suitable for cereals and starches which have a
high moisture content (approximately 10%). If the sample is in powder
form it can be dispersed in dehydrated solvent, allowing the moisture
content to be extracted for direct Karl Fischer titration. When using a
dehydrated solvent with sugars, solubility is sometimes enhanced if the
temperature is raised to 40-45 � C before titration. The moisture
vaporization method is suitable for the many items that do not dissolve
in solvents. Care needs to be taken with the heating temperature for
moisture vaporization. Temperatures in the 130-180 � C range are
commonly used. High temperatures may cause various phenomena,
including discoloration, abnormal results or failure to reach an end
point. In such cases the measurement must be repeated at a lower
temperature.
Moisture vaporization should be used with coulometric titration. Cereals
cannot be titrated directly as they do not dissolve in electrolytes.
Cereals are sometimes sampled after preliminary processing (e.g.
pulverization).
Care is needed to avoid moisture vaporization or absorption during
these processes.
Volumetric titration is the principal method used for dried vegetables.
The sample is added to the dehydrated solvent and stirred well for a
period of 5-10 minutes before direct titration. Moisture vaporization is
used when the moisture content cannot be fully extracted from samples
in this way. Karl Fischer titration can be carried out using either the
volumetric or coulometric methods. As moisture content tends to be
high, however, volumetric titration is usually preferable.
The precautions stipulated for moisture vaporization in connection with
cereals also apply to dried vegetables.
[Examples of Measurement]
(1) Volumetric titration
Reagents used: Karl Fischer Reagent SS-Z (or SS)
Dehydrated Solvent GEX, SU (or MS, FM) 25-50ml
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