Development of Karl Fischer Reagents

I-1. Questions & Answers about Karl Fischer Reagents
Q3
[Principle]
14
Memo "Titer"
This value is used to determine the quantity of a substance from the amount of
reagent titrated. It shows the equivalent amount of water per unit of volume and
is usually expressed as mgH20/ml.
[Procedures]
Could you outline the principle and procedures involved in
volumetric titration?
Karl Fischer titration is a volumetric analysis method that takes advantage of
the fact that iodine contained in Karl Fischer reagents reacts quantitatively
and selectively with water, as shown in the following formula.
I2 � SO2 � H20 � 3Base � CH3OH � 2Base � HI � Base � HSO4CH3
The quantification is based on the stoichiometrical principle that 1 mole of
iodine (254g) reacts with 1 mole of water (18g). In practice, the titer of a Karl
Fischer reagent is expressed as a water equivalent. Unlike normal
volumetric analysis methods, the concentration of iodine is not shown. For
example, Mitsubishi Chemical's SS-X Karl Fischer reagent is adjusted so
that 1ml will react with approximately 3mg of water, which means that the
solution contains approximately 42mg of iodine and has a 3mg titer. Once
the water equivalent of a Karl Fischer reagent is known, it is possible to
determine moisture content from the amount used (titrated).
a) A dehydrated solvent suitable for the sample is placed in a flask attached
to an automatic volumetric moisture meter (Figure 1).
b) The Karl Fischer reagent is titrated until all water has been eliminated
from the titration flask. (It is not necessary at this time to read the amount
titrated.) The titer of the Karl Fischer reagent is determined using water,
etc.
c) The sample is added.
d) The Karl Fischer reagent, the titer of which (mgH20/ml) has now been
determined, is titrated until the end-point is reached. The end-point is
detected electrically by means of a detection circuit built into the titration
system.
e) Moisture content is determined from the amount titrated according to the