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KARL FISCHER TITRATION

What is Karl Fischer Titration?

Karl Fischer titration is a widely used analytical method for quantifying water content in a variety of products. The fundamental principle behind it is based on the Bunsen Reaction between iodine and sulfur dioxide in an aqueous medium. Karl Fischer discovered that this reaction could be modified to be used for the determination of water in a non-aqueous system containing an excess of sulfur dioxide. He used a primary alcohol (methanol) as the solvent, and a base (pyridine) as the buffering agent.

What is the Karl Fischer Reaction?

ROH + SO2 + R’N  [R’NH]SO3R + H2O + I2 + 2R’N  2[R’NH]I + [R’NH]SO4R
[alcohol] [base] [alkylsulfite salt] [water] [iodine] [hydroiodic acid salt] [alkylsulfate salt]

The alcohol reacts with sulfur dioxide (SO2) and base to form an intermediate alkylsulfite salt, which is then oxidized by iodine to an alkylsulfate salt. This oxidation reaction consumes water. The reactive alcohol is typically methanol or 2-(2-Ethoxyethoxy)ethanol, also known as diethylene glycol monoethyl ether (DEGEE), or another suitable alcohol. Classic Karl Fisher reagents contained pyridine, a noxious carcinogen, as the base. The reagents most frequently used today are pyridine-free and contain imidazole or primary amines instead.

How does it work?

Water and iodine are consumed in a 1:1 ratio in the above reaction. Once all of the water present is consumed, the presence of excess iodine is detected voltametrically by the titrator’s indicator electrode. That signals the end-point of the titration. The amount of water present in the sample is calculated based on the concentration of iodine in the Karl Fisher titrating reagent (i.e., titer) and the amount of Karl Fisher Reagent consumed in the titration.


Is the Karl Fischer Reaction...