Development of Karl Fischer Reagents

9. Inorganic Gases
Key Points
Chapter II: Applications - 1
The moisture content of non-condensing gases, such as nitrogen,
oxygen and hydrogen, is captured by passing the sample gas through
a titration solvent or electrolyte.
Karl Fischer titration is then carried out. It is necessary, therefore, to
obtain and assemble equipment which includes pipes for the sample
gases and gas meters. Metal pipes should be used at the injection
ports. Pipes made of vinyl chloride or other plastics should be avoided
as these absorb atmospheric moisture.
For volumetric titration, an absorption solution is prepared by mixing a
general-use dehydrated solvent with propylene glycol in a ratio of 3:1.
For short periods, general-use dehydrated solvent can be used alone.
In such cases, changes in the quantity of the titration solvent, caused
by volatilization, must be monitored carefully.
For substances with low moisture content, accurate measurements can
be obtained by using a low-titer Karl Fischer reagent.
Because of the minute amounts of moisture in inorganic gases, we
recommend coulometric titration.
[Examples of Measurement]
(1) Volumetric titration
Place 150ml of dehydrated solvent in a titration flask. Titrate the Karl Fischer
reagent to the end point to remove all moisture. Next pass the sample gas
through the dehydrated solvent in the titration flask at a rate of 0.2-0.5l/min.
The flow of gas should be measured using a gas meter. Stop the flow of gas
(A) after the amount of water absorbed into the dehydrated solvent has
reached 5-50mg. Titrate (Bml) immediately using a Karl Fischer reagent with
a known titer (FmgH20/ml). Calculate the moisture content (W%) according
to the following formulae.
W (Vol%) =
W (Wt%) =
760
B �F�1.244 �––––––––– �
P
A �100
(273�t)
––––––––––––––––––
273
P
A � ––––––––– �
760
B �F
273
–
273 � t
M
� ––––––––– �1000
22.4
� 100
� 100
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