Metrohm 832 KF Thermoprep - Manual (Page 21)

4.5 Working procedure
832 KF Thermoprep, Operation
17
4.5 Working procedure
Warning!
As both the sample vials and the oven become very hot the sample
vials must be removed from the oven by using the crimping pliers. The
sample vials should only be placed on a heat-resistant surface.
In principle two different methods can be used.
For samples with a low water content one (or more) blank values
must be determined and subtracted from the water content determined
for the sample. Sample vials contain a considerable amount of atmos-
pheric humidity, e.g. Metrohm standard vials with a volume of 6 mL can
contain 60…150 µg water. While the determination is being carried out
atmospheric moisture can also enter the coulometer cell as a result of
leaks, etc.
For samples with a high water content blank value determinations
are not necessary as the atmospheric humidity contained in the vial is
negligible when compared with the moisture contained in the sample. If
no blank determinations are carried out then the whole procedure is
simplified and takes less time.
Determinations with the 832 KF Thermoprep basically take part in three
phases:
1. Preparing / Conditioning the system
2. Possibly determining the blank value
3. Determination of the sample
The procedure for determinations with the 756/831 Coulometer is de-
scribed below. A similar procedure can be used with a volumetric KF ti-
trator (e.g. 795 KFT Titrino).
Note
When using either a coulometer or a volumetric KF titrator it is abso-
lutely essential that an extraction time of at least 300 s is observed per
determination. More details are given in the Instructions for Use of the
particular instrument.