The reagent solution is composed of dominant iodine mixed with pyridine and methanol filled with sulfur dioxide.
The reaction principle of Karl-Fischer reagent with water is: based on the presence of water, iodine is reduced by sulfur dioxide, in the presence of pyridine and methanol, pyridine and methyl hydropyridine sulfate.
The reaction equation is:
H20 + I2 + SO2 + 3 C5H5N - > 2 C5H5N, HI + C5H5N, SO3.....................
(1)
C5H5N, SO3 + CH3OH and C5H5N, HSO4CH3..............................
(2)
In the electrolysis process, the electrode reaction is as follows:
Anode: 2I -- 2E -- I2............
(3)
Cathode: 2H+ + 2E → H2↑............
(4)
Iodine produced by the anode reacts with water until all the water reacts, and the end point of the reaction is indicated by a detection unit composed of a pair of platinum electrodes.
According to The Law of Faraday electrolysis, the number of molecules of iodine involved in the reaction is equal to the number of molecules of water, which is directly proportional to the amount of charge.
The following equation holds true for the amount of water and charge:
W = Q / 10.722.......................................................................................
(5)
Where: W -- unit of moisture content in sample: microgram
Q -- Unit of electrolytic capacity: millicoulomb
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