Karl Fischer titration methods
The Karl Fischer titration reaction uses volumetric or coulometric titration to determine the amount of water present in a sample from the oxidation of sulfur dioxide by iodine, in which water in a buffer solution is consumed.
This technique was discovered by Karl Fischer. Karl Fisher titration is a method for determining the moisture content of different types of substances. It relies on a reagent that reacts with the water content and turns the water content into a non-conductive chemical. Volumetric KF titration and coulometric KF titration are two techniques available for the Karl Fischer determination of water:
Volumetric Karl Fischer titration:
With this technique, the moisture content is determined from the volume or amount of reagent used to convert the water. The volumetric determination is suitable for the determination of the water content up to 1 % water. In this type of KF technique, samples are dissolved in a solvent before starting the titration, until the water has been removed, a reagent is added, and the endpoint is determined potentiometrically.
In this method, the Karl Fischer reagent contains a base buffer, alcohol, sulfur dioxide, and a recognized amount of iodine, which is needed to reach the titration endpoint.
Coulometric Karl Fischer titration:
The advantage of Karl Fisher's coulometric technique is the ability to accurately calculate the amount of moisture. Generally, this method is used if the moisture content is less than 1%. In this method, the solvents and the reagent are mixed in the titration cell and only need a solution containing iodide. The iodine required for the KF reaction produced by the anodic oxidation of iodide from solution and the end point are determined electrochemically.
The amount of iodine added to the sample is calculated by measuring the actual current required for the electrochemical generation of iodine. When reacting with water, the brown iodine solution is reduced to colorless iodide. In this method, sulfur dioxide, iodide ions, a base, and a solvent (alcohol) are used to complete the reaction.
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