Development of Karl Fischer Reagents

II-1. Organic Compounds
80
Note 2: It proved possible to add propylene oxide in three amounts of
1.7g (total: 5.1g). Thereafter the analytical readings rose until
finally, an end point was not reached.
With volumetric titration, it proved possible to add 50g and
measure this directly without any problems.
5. Phenols
Key Points
With most phenols the moisture content can be measured directly. As a
general rule there are no limitations with volumetric titration, but it is
important to be aware that limitations do exist in the case of coulometric
titration.
With volumetric titration, the sample is dissolved in a general-use
dehydrated solvent in the same way as for alcohols, before undergoing
Karl Fischer titration. Solubility is not a problem.
Aminophenols cannot be measured in methanol because of
interference reactions. Measurements can be taken, however, by using
a titration solvent prepared by adding salicylic acid to Dehydrated
Solvent MS (see "12. Amines"). The size of the sample used in such
cases should not exceed 2g.
In the case of coulometric titration, anodic oxidation produces a
precipitate that adheres to the anode. The resulting contamination of
the electrode precludes normal electrode performance and reduces the
efficiency of the current. An end point cannot be reached with
hydroquinone and aminophenols. This kind of interference is common
with coulometric titration, and care should be taken when using the
method. In tests carried out by Mitsubishi Chemical Corporation,
however, measurements have proved possible under controlled
conditions, as follows.
To 100ml of Aquamicron AX,
a) approximately 1g of phenol is added to begin with.
b) The total cumulative quantity added is approximately 5g. If there is
too much phenol the efficiency of the current will decline and
gradually lead to higher analytical values.