Metrohm 885 Compact Oven SC - Manual (Page 64)

8.1 Conditioning the system ￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭￭
54 ￭￭￭￭￭￭￭￭ 885 Compact Oven SC
8 Carrying out a determination
Moisture determinations according to the oven method require the condi-
tioning of the entire tubing system and of the KF titration cell before a
determination can be carried out. Because the sample vials and the sep-
tum seals may contain small amounts of moisture, three to five blank
value determinations must be carried out with sealed, empty vessels.
Solid or liquid samples are weighed in into sample vials, which are then
sealed. We recommend that the 6.2420.007 sample vials be used with
the 6.1448.067 septum seals (with screw cap). The silicone septum of the
aluminum cap is resistant to temperatures of up to 250 °C and has proven
itself to be exceptionally reliable.
8.1 Conditioning the system
The entire system must be conditioned prior to use, i. e. it must be abso-
lutely water-free. The oven must be heated to the desired working tem-
perature for this purpose. The needle must be inserted into a sealed sam-
ple vessel (conditioning vessel) in order to flush the entire tubing system
with the carrier gas. The gas supply is thus connected with the heating
tubing. This can all take place automatically in a normal method run.
8.1.1 Preparing the KF titration cell
Filling the KF titration cell
The KF titration cell must remain filled with conditioned working medium
when not in use. The working medium must be replaced from time to
time, even though the sample is not transferred into the working medium
using the oven method.
Prepare the KF titration cell as follows:
1 Fill the KF titration cell with working medium. We recommend
approximately 150 mL of working medium when using a coulometer
cell and approximately 35 mL with a volumetric KF titration cell. The
shaft of the heating tubing must, however, not be immersed.
2 Align the tip of the heating tubing against the vessel wall.
3 Switch on the stirrer. Set the stirring rate to high.