Metrohm's solution to Karl Fischer moisture analysis in difficult samples using elevated temperatures to release the moisture from the sample
Many substances, such as plastics or inorganic salts, release water only very slowly or at high temperatures.
Therefore they are not suitable for direct Karl Fischer titration.
Another problem is the low solubility of certain samples in alcohols.
In these cases, traditional methods recommend the use of harmful solubilisers or complex sample preparation steps.
Direct introduction of the sample into the titration cell can also contaminate the cell making it necessary to frequently change the reagents and clean the cell.
Finally, there are the various substances (for example ascorbic acid) that undergoes interfering side reaction with the KF reagents leading to incorrect results.
The above problems can be resolved with the KF Oven Method.
Here the substances to be examined are heated in a tube oven; carrier gas then transports the release water into the titration cell where it is determined by Karl Fischer titration.
As only the water releases the titration cell and the sample does not come into contact with the KF reagents, undesired side reactions and matrix effects are ruled out.
832 Thermoprep, the modern KF oven.
The 832 KF Thermoprep resulted from an improvement of the conventional Karl Fischer drying oven.
It applies the vial technique: samples are no longer introduced into the oven in weighing boats, but their own, perfectly sealed sample vial.
This gives the advantage that analysis can be performed under strictly reproducible conditions, which translates into improved precision.
Moreover, because sample preparation is reduced to a minimum, considerable time savings are obtained.
Easy sample preparation.
Sample preparation is straightforward and merely involves weighing the sample into the vial and sealing it with a crimping tool.
The hermetically sealing of the vessels with PTFE-coated septa prevents interferences due to humidity absorption from the ambient air.
For this reason, vials are used as standard in production plants.
The vial used in production areas can be of varying diameter and height.
In addition the dimension tolerances of the sample vessels depend on the manufacturer.
Metrohm has taken this into account in the design of its oven block, which has a variety of inserts and adapters to accommodate most customers' requirements.
The heatable transfer tubing for the 832 KF Thermoprep.
The 832 KF Thermoprep is now available with an optional heatable transfer tubing.
In particular, when the water is determined in the higher percentage range or at high temperatures, the water that is released from the sample can form a condensate in the transfer tubing, which produces too low and or erratic results.
In such cases, it is recommended to use a heated tubing guaranteeing complete transfer of the released water to the titration cell.
