Metrohm 860 KF Thermoprep - Manual (Page 47)

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860 KF Thermoprep ￭￭￭￭￭￭￭￭ 39
8 Appendix
8.1 Practical instructions
Carrier gas selection
If the hot sample is sensitive to air or oxygen (decomposition) and releases
substances that disrupt the KF reaction, then nitrogen (N
2
) should be used
as the carrier gas.
Temperature settings
The temperature selected should be as high as the sample allows (high
temperature = shorter analysis time). The sample may not however
decompose. It must not give off any oxidizable substances, only water.
The displayed temperature refers to the temperature in the heating block
and not to the sample temperature. Depending on the size of the vial
used, the gas flow and the temperature setting, the effective temperature
of the sample can deviate up to 10%.
Gas flow
If the needle is inserted into the sample vessel until it stops, then the gas
flow moves through the sample and then through the outlet needle into
the titration vessel where the moisture is titrated. If the needle is not per-
mitted to dip into the sample, then a longer needle holder can be used,
see the chapter "Optional accessories".
The gas flow should be kept as low as possible. Particularly in the case of
very moist samples, care must be taken to ensure that excessively large
quantities of water are not released too quickly into the titration vessel. In
addition, there is the danger of condensate formation in the heating tube.
The working medium in the cell must be able to absorb the moisture that
is expelled without delay. Normally, a flow rate of 40...60 mL/min is opti-
mal.
Extraction time
An extraction time of a minimum of 5 minutes should be set on the titra-
tor in order to prevent the titration from being stopped before the sample
has released its water.
Conditioning the system
The system must be conditioned with an empty, sealed sample vial (condi-
tioning vessel) before a determination is made.