Metrohm 832 KF Thermoprep - Manual (Page 24)

4.6 Practical information
20
832 KF Thermoprep, Operation
4.6 Practical information
Selecting the carrier gas
Nitrogen (N
2
) should be used as the carrier gas if the hot sample is sen-
sitive to air or oxygen (decomposition) or releases substances which in-
terfere with the KF reaction.
Temperature setting
Select as high a temperature as the sample allows (high temperature =
short analysis time). However, the sample must not decompose. It
should not release any other oxidizable substances than water. The
temperature shown on the temperature controller refers to the tempera-
ture in the aluminum heating block and not to the sample temperature.
Depending on the size of vial used and the temperature setting, the
sample temperature could vary by up to 10%.
Gas flow
The gas flow is set on the flow controller on the front panel of the 832
KF Thermoprep and passes through the drying bottles. The gas flow
should be kept as low as possible. With very moist samples in particular
care must be taken that large amounts of water do not enter the titration
vessel too quickly. The solution in cell must be able to absorb the
driven-off moisture. A flow rate of 40…60 mL/min is normally optimal.
If the needle is inserted in the sample bottle until the stop is reached
then the flow of gas through the sample will be transferred to the titra-
tion vessel via the outlet needle. The moisture is then titrated in the titra-
tion vessel.
Extraction time
An extraction time of at least 5 min should be set on the connected ti-
trator, in order to prevent the titration from being stopped before all the
sample has released all its moisture.
Conditioning the system
Before a measurement the system must be conditioned with an empty
sealed sample vial (conditioning vessel).
Literature
• Hydranal ® Manual, Water reagents for Karl-Fischer-Titration, Riedel-
de Haën, 1987
• The following Metrohm Application Bulletins can be obtained free of
charge:
No. 109 Karl Fischer water determination with the KF drying
oven
No. 145 Determination of low water contents in plastics using
the KF oven method
No. 217 Karl Fischer water determination in pharmaceuticals us-
ing the oven method