As you know the Karl Fischer Method of moisture analysis has a reputation of being water specific. The method works through the use of a special Karl Fischer Reagent.Basics of Karl Fischer
As a quick review, the material to be tested is dissolved in a solvent. The water is released and converted by the reagent. This process happens inside an enclosed airtight titration cell.
The amount of reagent needed to make full conversion is a measure of moisture. Note that the material to be tested is dissolved in the presence of the reagent.
When Basic Karl Fischer will Not Work
As with many testing methods there are complications. Some substances are difficult to dissolve and require solvents that operate on the Karl Fischer reagent to cause side reactions that distort the water content calculation. Other materials only release the water at high temperatures. In these cases the simple process of dissolving the sample in the presence of the Karl Fischer reagent won't work.
Solution to the Problem Samples
The answer to side reaction problems or high temperature exigencies is an instrument known as a Karl Fischer Oven or Evaporator. A Karl Fischer Oven consists of a heating tube in which the temperature can be controlled between 60ºC to 300ºC. Provision is made for a carrier gas to flow through this heating tube and move the escaping water into the titration cell. When the sample is ready to be tested, it is placed into the heating tube (operating at the appropriate temperature for the sample). As the moisture is released, the vapor is transported by the gas (usually dry Nitrogen) to the titration cell where it is bubbled into the reagent. The Karl Fischer process is completed and the moisture content calculated. Some of the materials that need to be processed in an oven are plastics and salts. These Karl Fischer Oven/Evaporators are used with standard Karl Fischer Titrators. When the moisture content is low (<1%) the Coulometric technique is recommended, otherwise a Volumetric Karl Fischer titrator is used.
For more information on the Karl Fischer Moisture Method click here.
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