Product category:
Humidity and moisture sensing systems
News Release from: Metrohm UK | Subject: KF Oven Method
Edited by the Processingtalk Editorial
Team on 27 August 2007
Moisture analysis in difficult samples
Many substances, such as plastics or inorganic salts, release water only very slowly or at high temperatures: to determine moisture content the sample can be heated in a KF Oven
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
This article was originally published on Processingtalk on 3 Apr 2008 at 8.00am (UK)
Related stories
Water determination in pharmaceuticals
The Karl Fischer (KF) Oven Method permits the accurate, precise and straightforward determination of the water content of pharmaceuticals that are not amenable to direct KF titration
Tighter process control in acid pickling baths
Online ion chromatography from Metrohm has enabled tighter process control of acid pickling baths, as the final cleaning stage prior to metal plating
Another problem is the low solubility of certain samples in alcohols.
In these cases, traditional methods of moisture analysis 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.
Further reading
The determination of acidity in soft drinks
Sparkling drinks are the main cause of increasing tooth erosion among teenagers: a study in the British Dental Journal found a strong link between fizzy drink consumption and tooth erosion
The new Metrohm 856 conductivity module
The 856 Conductivity Module introduces the new 5-ring conductivity sensors which are far superior to the classical conductivity sensor
Finally, there are the various substances (for example ascorbic acid) that undergoes an 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.
The 832 KF Thermoprep resulted from an improvement of the conventional Karl Fischer drying oven.
It applies the vial technique: The 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.
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 have taken this into account in the design of their oven block, which has a variety of inserts and adapters to accommodate most customer requirements.
The 832 KF Thermoprep is now available with an optional heat-able 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. Request a free brochure from Metrohm UK ...
• Metrohm UK: contact details and other news
• Email this article to a colleague
• Register for the free Processingtalk email newsletter
• Processingtalk Home Page
Search the Pro-Talk network of sites
