K arl F ischer Moisture Determination

Abstract

Abstract The Karl Fischer (KF) titration is a method of determining the water content of solid, liquid and gaseous samples. It is the technique preferred for use in industrial quality control. In principle it involves the oxidation of sulfur dioxide by iodine, in the presence of water, in a buffered solution. An alcohol is used as the preferred solvent. The water is converted stoichiometrically and therefore its quantity is determined indirectly. The end‐point (EP) is reached when there is an excess of iodine. It can be indicated visually, photometrically or electrochemically. According to state‐of‐the‐art technology a double platinum electrode determines a voltammetric indication. The KF titration can be carried out either volumetrically or by coulometry. For a volumetric titration the iodine is added by volume to the titration cell containing the sample. In a coulometric titration iodide is oxidized at a platinum electrode and the iodine formed reacts with the water. The amount of current necessary in the generation of the iodine is directly related to the quantity of iodine generated, according to Faraday's first law. In practice, special titrators for the KF titration are available. Preformulated reagents are similarly available ready for use. Water in an extensive number of materials can be determined by KF titration. Chemicals, pharmaceuticals, oils, plastics and foodstuffs are examples of typical sample types. The measurement range spans a few ppm to 100% water. The KF titration is described in ISO 760 and as part of many other international standard procedures. Other methods for the determination of water content include loss‐on‐drying, IR spectroscopy or azeotropic distillation.