Metrohm®
Karl Fischer Ovens®
The KF oven method
Substances that release their water slowly or at high temperatures (e.g., plastics
or inorganic salts) are not suitable for a direct Karl Fischer titration. Other samples have a low
solubility in alcohols, which may involve toxic solvents to promote dissolution and/or involve extensive
sample preparation. Introducing these samples directly into the titration cell may contaminate it,
and thus require you to exchange the titration solution and clean the cell frequently. There are still
other substances that undergo side reactions with the KF reagents (e.g., ascorbic acid), which lead
to false results.
All of these problems can be avoided by using the KF oven method: the sample is heated
in an oven and a carrier gas transfers the released water to the titration cell, where it is then
determined by Karl Fischer titration. Since only the water enters the KF cell and the sample itself
does not come into contact with the KF reagent, unwanted side reactions and matrix effects are eliminated.
Unique sampling system purges moisture from heated headspace vials into the titration vessel for
analysis. |
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Sophisticated construction
Metrohm ovens have evolved from the conventional tube oven. However, instead of
introducing the sample into the oven by means of a sample boat, a vial technique is used. The sample
is weighed directly into a small sample vial, sealed with a septum cap and transferred to the oven.
This brings decisive advantages:
- Strictly reproducible conditions yield results with improved precision
- Manual sample preparation is minimized
- There is no contamination of the oven or titration cell by the sample; consequently, there
are no carryover and memory effects
- The reagent consumption is diminished since the solvent is exchanged less frequently
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Two Metrohm ovens are available: the 832 KF Thermoprep for manual, individual samples;
and the 774 KF Oven Sample Processor for automation of multiple samples. Both are very compact instruments
that feature integrated heating block, gas pump, flow meter and drying flasks.
Common applications:
- Petrochemicals, including fuels, oils, crudes, hydraulic fluids and lubricants
- Polymers, including pellets, polymer/solvent mixtures, raw materials and precursors
- Pharmaceuticals, including powders, liquids, tablets/pills and lyophilized samples
- Any sample run currently using a conventional Karl Fischer oven, such as food, salts, metals,
soaps and toothpaste
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