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Karl Fischer Reagents for Analytical Techniques - Alfa Aesar

KARL FISCHER TITRATION

Alfa Aesar is proud to introduce our line of Karl Fischer Reagents. Please contact us if you have any questions.

Karl Fischer titration is an analytical technique to measure the amount of water contained in various samples, which may be solid, liquid or gaseous. This method was originally developed in the 1930s by a German chemist Karl Fischer.

Karl Fischer titration is based on a 1:1 reaction between iodine and water in the presence of sulfur dioxide and a base. The reagent used for the titration needs to contain the following:

  • Alcohol - methanol was used originally, but in di?erent variations of the reagent can be replaced by ethyl carbitol, methoxypropanol, ethanol, etc.
  • Sulfur dioxide
  • Iodine
  • Base - pyridine was used initially, but has since been replaced by imidazole, which assures a higher rate of reaction and is less toxic

One of the most important developments in Karl Fischer titration chemistry was the replacement of pyridine with imidazole. Pyridine is a relatively weak base and the equilibrium of the reaction is not completely shifted toward the products. As a result, use of pyridine-based reagents typically resulted in slow reactions and unstable endpoints. This, in turn, negatively impacted reproducibility of measurements.

Imidazole is a stronger base and shifts the reaction equilibrium completely to the right, which results in a faster titration rate and more stable endpoints.

TYPES OF KARL FISCHER TITRATION

Karl Fischer titration is based on the stoichiometric reaction of iodine with water. There are two methods of introducing iodine into the sample - addition of molecular iodine in a solution with a volume of a reagent (volumetric titration) and generation of iodine electrochemically within the titration cell (coulometric titration).

Volumetric titration has the benefit of speed and generally lower cost, while coulometric titration allows for accurate analysis of samples with low moisture levels. The two main methods have their own variations and both make use of calibration standards to verify accuracy of the measurements.

  • Karl Fischer Composite K2, for volumetric one-component titration, for ketones and aldehydes
  • Karl Fischer Composite K5, for volumetric one-component titration, for ketones and aldehydes
  • Karl Fischer Composite T1, for volumetric one-component titration
  • Karl Fischer Composite T2, for volumetric one-component titration
  • Karl Fischer Composite T5, for volumetric one-component titration
  • Karl Fischer Coulometric AG, anolyte solution, for cells with or without diaphragm
  • Karl Fischer Coulometric AG-C, for oils, does not cont. xylene, anolyte solution, for cells with diaphragm
  • Karl Fischer Coulometric AG-Oil, anolyte solution, for cells with or without diaphragm
  • Karl Fischer Coulometric CG, catholyte solution
  • Karl Fischer Methanol, solvent/working medium for volumetric one-component titration
  • Karl Fischer Solvent CS, solvent for volumetric titration, for oils
  • Karl Fischer Solvent KT, solvent for volumetric one- and two-component titration, for aldehydes and ketones
  • Karl Fischer Solvent, solvent for volumetric two-component titration
  • Karl Fischer Titrant K2, for volumetric two-component titration, for ketones and aldehydes
  • Karl Fischer Titrant K5, for volumetric two-component titration, for ketones and aldehydes
  • Karl Fischer Titrant T2, for volumetric two-component titration
  • Karl Fischer Titrant T5, for volumetric two-component titration

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