Karl Fischer Titration

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Karl Fischer titration is a special type of titration method used to determine the small amount of water in the given sample. This method was invented by Karl Fischer in 1935 AD, named the process from his name as Karl Fischer titration. This method uses a special type of reagent called Karl Fischer reagent for the quantitative analysis of water in the sample.

Principle of Karl Fischer Titration:

The basic principle of Karl Fischer titration involves the oxidation reaction between water and iodine in presence of sulfur dioxide (SO2) and a base. The end point is detected by consumption total amount of water present in the sample. The reaction for Karl Fischer titration is given as:

Methanol is used as a solvent in this method.

Major chemicals used in Karl Fischer titrations are :

  1. Alcohol: Methanol (CH3OH) used mainly but ethanol, methoxypropanol etc can also be used.
  2. Sulphur dioxide (SO2)
  3. A base (RN): pyridine is mainly used base but imadizole is also used due to less toxicity.
  4. Iodine (I2)
  5. Sample containing water molecule

Process of Karl Fischer titration :

In this method of analysis, there is an oxidation reaction between iodine and water in the ratio of 1:1. The chemicals i.e. methanol, sulfur dioxide, and a base produces Karl Fischer reagent for accurate and precise determination of water molecules. When all the water molecules are consumed, the end point is detected

Types of Karl Fischer titration:

  1. Volumetric Karl Fischer titration:

This method is used to determine the amount of water above 100 ppm. In this method, iodine is added during titration. The end point is detected by the potentiometric method.

2. Coulometric Karl Fischer titration:

This method is used for the trace amount of water 1ppm to 5%. In this method, iodine is liberated during titration. The end point is detected by the electrochemical method.

Applications of Karl Fischer titration:

The major applications of KFT are :

  1. In industries
  2. In pharmaceuticals
  3. In cosmetics
  4. In technical products like plastics, oils, gases etc.
  5. In food products to determine the amount of water.

–By Nirmal Karki

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