Buchi DuMaster D-480, Operation Manual

Page: 177 / 354

Operating instructions DuMaster D-480 ©BÜCHI Labortechnik AG
8 - Maintaining the instrument 177
CalibrationLow (0 - 300 mg):

O
2
dosing time 90 sec.

O
2
flow = 225 ml/min.

O
2
cut-off threshold = 15 %.
CalibrationHigh (300 - 700 mg):

O
2
dosing time 150 sec.

O
2
flow = 300 ml/min.

O
2
cut-off threshold = 20 %.

Start the analysis process by selecting
System > Auto run
.

Check whether the O
2
field "MFC O2" on the screen displays the expected setpoint value during
the combustion time. See Values for oxygen dosing.

Observe the measuring results. If the N blank value is not below 50 after stabilization: Stop
continuous analysis via
System > Single
. Find out the reason of the increased blank value and
correct it. Cf. Types of blank value determination and their settings.

Save the original values. See
Data backup and printing
(on page 156).
Phase 2: Ascertaining appropriate calculation methods
Proceed as follows:

Execute the following command:
Math. > Calibration
. If sequential blank value determination is
activated a message window opens showing the corresponding information.

Click
Yes
to continue. The "Configure calibration" dialog appears.

Define the following settings:

Check the box next to "Two calibration ranges".

Enter 1 as the polynomial degree for the lower and upper range. This corresponds to linear
calculation.

Click
OK
to save your settings and close the dialog. The "Specify lower and upper calibration
range" dialog appears. It displays a graph generated from the absolute contents of the samples
and their peak areas in a linear calculation. The graph displays deviations of the measuring
points from these lines.

Observe the measuring points and decide

what calculation would be suitable

whether you would separate the the ranges

and, if so, where you would separate the ranges.
See
Calibration curve calculation method criteria
(on page 52).

Write down your considerations.

Click
OK
to view the readings for the other elements. For each element, decide as described
before.

Write down your considerations.

Click
Cancel
.
Phase 3: Set calculation methods, perform calculation
Proceed as follows:

Execute the following command again:
Math. > Calibration
. If sequential blank value
determination is activated a message window opens showing the corresponding information.

Click
Yes
to continue. The "Configure calibration" dialog appears.

Define the settings that you ascertained in the preceding phase.