Coulometric titration of water by the Karl Fischer reaction

10 Coulometric titration of water by the Karl Fischer reaction 

Many manufactured products, as well as solvents and raw materials are analyzed for their water content (percent humidity). Of all the available methods, the Karl Fischer titration is perhaps the most widely used, accounting more than 500 000 determinations performed daily world-wide. 

The Karl Fischer method is applied in a multitude of substances from finished products (butter, cheese, dried milk sugar, etc.) to solvents and other industrial products (paper, gas, petroleum, plastic films, etc.). Solids and not soluble samples must, prior to the measurement, either be ground into powders, extracted with anhydrous solvents, eliminated as azeotropes or heated to evaporate the water in special accessories. The only difficult cases are encountered with strongly acidic or basic media since they denature reactants as well as ketones and aldehydes which perturb the titration through formation of acetals (special reagents must be used for these instances). 

This method of titration may be sub-divided into two main techniques volumetric titration making use of a titrator (a potentiograph) with end point detection, and coulometric titration making use of a coulometer, more sensitive for measurement of very low levels of water (concentrations in the order or below 1 mg/L). 

In the presence of water, iodine reacts with sulfur dioxide through a redox reaction that is specific to these three compounds  

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COULOMETRIC TITRATION OF WATER BY THE KARL FISCHER REACTION... 

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