Correct sample preparation of solid or semi-solid substances for water determination with volumetric Karl Fischer Titration

The water determination of solid or semi-solid substances shows inconsistent results, sometimes too high, sometimes too low.

Possible reasons:

The sample does not or only partly dissolve in Karl Fischer solvents and the water releases incompletely due to strong entrapment in the sample’s structure.

Recommendations:

It is necessary to crush insoluble solids to gain access to the trapped water. A very hard sample such as minerals, hard salts, or similar shall be ground in a closed, cooled analytical mill. Hard, brittle samples such as grain, noodles, and coffee beans shall be crushed in a blending device. Moderately hard, brittle samples such as chips, candies etc. are best homogenized by pulverizing the sample in a mortar. Jellied fruits, almond paste, butter, margarine shall be cut into small pieces with scissors or a knife. Grate hard and fatty samples such as chocolate soft and fatty samples such as sausage, meat, cheese and then reduce it further to small pieces with a homogenizer in an external solvent. Vegetable juices and fruit juice extracts shall be thoroughly shaken or homogenized with a high speed stirrer or a blending device.