Determination of Water Content by Karl Fischer Analysis
Karl Fischer titration (KF) is a method in analytical chemistry that uses coulometric, volumetric, or oven methods of titration to determine trace to percent level amounts of water in a sample.
The Karl Fischer titration is very popular due to several practical advantages that it holds over other methods of moisture determination, such as accuracy, speed, and selectivity. KF is selective for water, because the titration reaction itself consumes water. In contrast, measurement of mass loss on drying will detect the loss of any volatile substance. KF has a high accuracy and precision, typically within 1% of available water, e.g. 3.00% appears as 2.97 - 3.03%. The KF response is linear and normally only takes minutes to perform. Therefore, single-point calibration using a calibrated 1% water standard is sufficient and no calibration curves are necessary.
With KF, little sample preparation is needed. For volumetric and coulometric methods, a liquid sample can usually be directly injected into the titration cell using a syringe. The main difference between the two is that with the volumetric method the titrant is added directly to the sample by a burette, while with the coulometric method the titrant is generated electrochemically in the titration cell. For the oven method, solid samples are sealed in glass vials before being introduced into the oven, where the water content is pulled out and funneled with a carrier gas to the coulometric titration cell where it is consumed and quantified.
Impact Analytical provides Karl Fischer titration services to determine water content in both liquid and solid materials. Our laboratory is equipped with both volumetric and coulometric titrators, as well as an oven attachment for analysis of solids. Volumetric KF can determine water in the 0.1-100% range, while coulometric KF is used for lower water concentrations in the 0.001-5% range.