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CA-200
Section 1: Measurement Principle
Model CA-200 measures moisture by applying Karl Fischer reaction to coulometric titration.
In this coulometric titration, supply electrolytic solution mainly composed of iodide ions, sulfur
dioxide, and alcohol to a titration cell. Iodine for titration is internally generated by electrolysis.
* Karl Fischer reaction
Water reacts with iodine and sulfur dioxide in base and alcohol.
H
O + I
+ SO
2
2
* Coulometric titration
Iodine is generated from iodine ions by electrolysis in the anode solution containing iodine ions.
-
2I
- 2e
When iodine generated by the reaction of the formula (2) is consumed according to the formula
(1), the consumption of iodine is detected by a detector electrode and iodine is generated again
from an anode by electrolysis according to the formula (2). The generated iodine is proportional to
electric quantity by "Faraday's law".
From the formula (1), the ratio of reaction of H
Therefore, 1 mol (18g) of water corresponds to 2×96500 coulombs and 1mg of water
corresponds to 10.72 coulombs.
Based on the above principle, moisture content is calculated from the electricity for electrolysis.
+ ROH + 3Base
2
I
2··········································································································································
2
2Base
•
HI + Base.....HSO
O and I
is 1 : 1.
2
1-1
Section 1: Measurement Principle
R (1)
4
(2)
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