Substances like plastics or inorganic salts are not suitable for direct Karl Fischer titration, but can have their water analysed by the KF oven technique
Many substances (eg plastics or inorganic salts) release their water only slowly or at high temperatures.
They are therefore not suitable for direct Karl Fischer titration.
An additional problem is the low solubility of certain samples in alcohols.
In these cases traditional methods recommend the use of toxic solvents to promote dissolution or alternatively extensive sample preparation procedures.
Moreover, if the sample is introduced directly into the titration cell the latter can be strongly contaminated, which means that it is necessary to exchange the titration solution and clean the cell frequently.
Finally there are various substances (eg ascorbic acid) that undergo side reactions with KF reagents thus falsifying the result.
By using the KF oven technique, the above problems can be avoided.
The substance under investigation is heated in a tube oven and the released water is transferred by a carrier gas into the titration cell where it is titrated.
Based on the extremely successful Metrohm 774 automated oven processor the new Metrohm 832 Thermoprep has been developed for single determinations.
The vial technique is applied, ie, the samples are no longer introduced into the oven by means of a sample boat, but in their own tightly sealed vials.
Combined with the refined methodology of the compact KF Thermoprep this brings decisive advantages: Strictly reproducible analysis conditions for all samples, this is shown by the considerably improved precision of the results.
Manual sample preparation is reduced to a minimum, just 'weigh, crimp, and analyse'.
Considerable savings in time and money.
No contamination of the oven, consequently there is no carryover and memory effects.
Improved water release from the sample as the carrier gas does not just pass over the sample but directly through it.
Depending upon the samples water content, the analysis can be carried out volumetrically, for high levels, or coulometrically, for trace amounts.
The construction of the 832 Thermoprep oven is so flexible that it can be used for all vial sizes, both larger and smaller than the standard Metrohm vials.
