Development of Karl Fischer Reagents

Q12
Chapter I: Basic Knowledge
How can we actually measure moisture content using coulometric
titration? Please describe the preparations and procedures involved.
To measure moisture content by means of coulometric titration, you will first
need to prepare the following items.
�Electrolytes: Aquamicron series
To ensure proper functioning, it is essential to use the correct
anolyte-catholyte combination.
�A Karl Fischer coulometric titration system
(Aquamicron series products manufactured by Mitsubishi
Chemicals can be used with most commercially available
systems.)
Next, the size of the sample is determined according to the anticipated
moisture content.
There are actually two coulometric titration methods.
(1) Direct titration (2) Moisture vaporization
1. Sampling amounts
Coulometric titration is suitable for the measurement of trace quantities of
moisture. Sample size is an important consideration as excessive quantities
will extend the time required for analysis.
Normally a sample containing 0.1-5mg of water is used. The guidelines in
the following table assume that the appropriate moisture content range for
coulometric titration is 1% or lower. This is not to say that coulometric
titration cannot be used for samples with a moisture content above 1%. In
such cases, however, the need to obtain samples in extremely small
quantities will increase measurement errors, leading to problems with
accuracy. If possible, volumetric titration should be used in such cases.
Anticipated moisture content (%) Sample quantity (g)
0-0.05
0.05-0.1
0.1-0.2
0.2-0.5
0.5-2.0
5-10
2
1
0.5
0.1
2. Obtaining a Sample
A carefully dried syringe (1-10ml) should be used. First, flush the syringe 2-3
times with the sample substance. Next, the amount required for the sample
should be taken. A piece of silicon rubber should be attached to the end of
the syringe needle, and the syringe should then be weighed precisely.
The silicon rubber should then be removed, and the sample inserted into the
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