Metrohm 774 Oven Sample Processor - Manual (Page 46)

4 Oven control and gas flow
774 Oven Sample Processor, Instructions for use 40
4.3 KF Moisture determination
The 774 Oven Sample Processor is predestined for Karl Fischer moisture
determinations. The oven method is used for those samples in which the di-
rect determination of the water content is either impossible or very difficult.
This applies for substances which either directly react with the Karl Fischer
reagents or only release their moisture very slowly into the reaction solution
because of their insolubility, e.g. plastic granulates or oils.
The principle of the oven method with the 774 Oven Sample Processor:
Preparation:
• The samples are weighed into sample vials and tightly sealed with a
PTFE-coated septum. The sample weights are entered on the Coulom-
eter or KF Titrator.
• The sample vials are placed on the rack and the sample oven is heated
up.
• A sealed but empty sample vial is used as the conditioning vial and is
placed in the rack position intended for it.
Conditioning and blank determination
• The conditioning vial is moved to the oven and the lift is lowered to the
rinsing position. The needle penetrates the conditioning vial septum.
• The gas flow is now switched on in order to purge the complete tubing
system and to provide reproducible and constant conditions.
• The measuring cell is now conditioned with a Coulometer or KF Titrator
until the reaction medium is sufficiently dry.
• The gas flow is switched off and a blank sample is moved into the oven,
the gas flow is switched on again and a blank value determination is
carried in order to determine the influence of the surroundings during
the heating-up period. The moisture released during a constant heating-
up period (similar to the sample heating-up period) or the moisture in
the empty sample vessel and the basic drift per unit of time can be de-
termined separately.
• When the determination of the blank value has been completed the re-
action medium is reconditioned.