Loss on Drying

The simplest is Loss on Drying, which involves heating a material at 105°C until a constant weight is achieved. This is a simple, direct, and effective method for many products. However, it cannot be used on thermally unstable products, or products which contain (or potentially contain) other volatile materials.

Karl Fischer Titration

A more specific method is the Karl Fischer titration. This relies on the reaction of water with sulfur dioxide and iodine in the presence of base. It is a well known, well understood reaction. It is easily automated, with many automatic titrators available. However, it is not without potential problems. Many samples are hygroscopic, absorbing atmospheric moisture during handling. Also, the sample must be dissolved in a suitable solvent prior to titration, but the solvent itself must be as anhydrous as possible. Methanol or pyridine are frequently used. Finally, some compound types, especially aldehydes and ketones, will interfere with the Karl Fischer titration, necessitating the use of different reagents.

Formerly West Coast Analytical Service (WCAS) and Bodycote Testing Group