(I) Analytical principles In the classical Karl Fischer capacity titration process, iodine reacts with sulphur dioxide in the presence of water as follows:

H2O I2 SO2 CH3OH 3RN→2RN·HI RN·HS04CH3 ....................... (1)

The iodine required for the reaction is supplemented by the addition of a standard solution containing iodine.

The coulometric method (coagulation method) is based on the dissolution of a sample in an electrolyte containing a specific solvent containing certain iodine. Water consumes iodine. The required iodine is no longer titrated with standard iodine-containing reagents, but electrolysis. The process of oxidation of iodide ions in solution to iodine:

2I———2e—→I2..................................................................(2)

The iodine produced reacts with the water in the sample and the end point is indicated with a double platinum electrode. When the concentration of iodine in the electrolyte returned to its original concentration, the electrolysis was stopped. Then according to Faraday’s law of electrolysis:

m=×=

Where: m - weight of water in the sample, mg;

C - Electricity consumed by electrolysis, mc;

M - the molecular weight of water;

n - number of electron transfer;

i - electrolytic current, mA;

t - electrolysis time, s;

96500 - Faraday constant;

10722 - The amount of electricity consumed to electrolyze 1mg of water, mc.

By entering the required parameters into the instrument microcomputer, the moisture content of the analysis sample can be expressed in ppm or %, μg.

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