Karl Fischer Sample Preparation

Insoluble Samples
These are pulverized using a ball mill, grater, or mixer. The water is extracted using a suitable anhydrous solvent or the sample is heated using a desorption oven to evaporate the water and then the water vapor is transferred to the titration vessel.

Liquid Samples
For liquids that have a low solubility in methanol, such as oils, a solvent mixture is required for the titration (chloroform is usually added). Otherwise, no preparation is required prior to testing.

Samples that react with components of the "Fischer" reagent can cause difficulties in moisture measurements. These include aldehydes, ketones, carboxyllic acids, thiols, and certain amines.

For samples that are insoluble in the anhydrous solvent, that could react with the Karl Fischer reagents, or for which the sample preparation must be simplified, a thermal desorption drying oven such as the Mettler DO302 Drying Oven produced by Mettler Toledo, Inc., Highstown, N.J. can be used. This oven drives off the water from the sample and then transports the moisture into the titration cell by means of a purge gas.