BUCHI DuMaster D-480 - Manual (Page 138)

Operation Manual D-480 ©BÜCH Labortechnik AG
7 - Using the instrument 138
Animal feed, approx. 500 mg medium fat content 50 mgFeed 250 ml/min, 100 sec
Cheese, sausage, appr. 500 mg high fat content 500fatCheeseSausage 300 ml/min, 150 sec
Blank value with O
2
Blank with O2 80 ml/min, 60 sec
Blank value without O
2
Blank without O2 50 ml/min, 1 sec
Beer, milk, soil, appr. 500 mg medium fat content 500mgBeerMilkSoil 120 ml/min, 60 sec
Starch, approx. 400 mg 400mgStarch 250 ml/min, 150 sec
Soil, approx. 250 mg 250mgSoil 100 ml/min, 60 sec
Optimize O
2
dosing
If your sample matrix is always the same, it is advisable to optimize oxygen dosing for reasons of
costs. Proceed as follows:
 Measure a typical sample of known element content several times with the same sample weight
(max. ± 2 mg fluctuation).
 Systematically increase O
2
cut off threshold until you get a false low reading or a substantial
widening of the N peak.
 Set the O
2
cut off threshold of the last successful measurement before the false low reading
occurred. These settings are optimal for this matrix and sample weight.
 Check whether oxygen dosing is generally usable. To do so, measure several known samples of
similar matrix.
Example for optimization of oxygen dosing
O
2
cut off threshold = 30 %, total O
2
amount = 589 ml
O
2
cut off threshold = 40 %, total O
2
amount = 478 ml
Performing measurements
What you need to know
You must have read the Oxygen dosing values (on page 137) section so that you can set the
correct values for measuring.