BUCHI DuMaster D-480 - Manual (Page 127)

Operation Manual D-480 ©BÜCH Labortechnik AG
7 - Using the instrument 127
The result will be that the nitrogen content is well measurable and you will achieve an optimum in
catalyst consumption as well as in maintenance effort. Generally, you should prefer to carry out
multiple measurements with lower weights instead of fewer measurments with higher weights.
Determining sample weight with unknown substances
Proceed as follows:
 Start with a sample weight at approx. 300 mg.
 Observe the behavior of the pressure during combustion at the flow meters of the instrument.
 It has to be observed that during combustion phase the PC display "Flow CO2" does not drop
below 200 ml/min. Otherwise there is a risk of pressing soot and tar into the gas supply tubes
(soot filter will turn to a dark color).
Caution: In case of too high combustion pressure (PC display "Flow CO2" shows 0) the gas flow
control unit of the instrument will soil!
Showing or hiding the weight window
Showing or hiding the weight window
Select View > Weight window to show or hide the weight window:
 If "Weight window" is checked, the weight window is displayed.
 If "Weight window" is not checked, the weight window is hidden.
Packing samples
Sample packing
The following types of sample packing may be used depending on the type of sample:
 Foils
 Boats
 Capsules
 Pelletizing in nitrogen-free paper
 Pelletizing wihout packing material
The following sample packing materials may be used depending on the type of sample:
 Tin
 nitrogen-free paper
Sample packing rules
Observe the following rules in order to achieve reliable measuring results:
 There must be no body fat or sweat on the packing material. Therefore, do not touch the boats or
other packing material with your hands. Work with tweezers or with gloves. Flush capsules free
of air with CO
2
if necessary.
 Avoid loss of substance after weighing. Therefore, wrap the substance exactly in the foil and
close capsules gas-tight.
 Minimize air inclusions in the sample material as they distort the N value. Therefore, compress
sample packets and flush capsules free of air.