9-22 FI/FD Operation
5. In the Tuning Setup dialog box, Time pane set the Scan Time(s) to 1.2
and the Inter Scan Delay (s) to 0.2
6. In Data pane, click Continuum from the Data Format list.
7. Increase the Extraction Voltage in increments of 2000 V to a maximum
of 12,000 V.
8. In the FI tab, specify an emitter current of 8 µA.
Ensure the readback indicates that the current is passing through the
emitter. If no current or less than 8 µA passes through the emitter, the
emitter could be damaged and need replacing.
See also: Changing an emitter on page 10-33.
9. Set the emitter current to the maximum value in mA for 2 to 4 seconds.
Rational: This desorbs any condensed material on the emitter and
ensures maximum sensitivity.
10. Set the emitter current to zero.
11. Click Flash Off Emitter.
12. Set the Flash Off Current to 40 to 80% of the maximum emitter current.
Note: Ensure that a steady signal is maintained when the flash-off value
is used. If there is a drop in sensitivity, increase the flash-off current.
13. Set the Emitter Current to 0 mA.
Tip: The emitter heats up during the interscan delay and cools down
during the scan. This ensures that the sample does not condense on the
emitter suppressing the sensitivity.
Caution:
• Monitor the readback of the Extraction Control pane Current
Leakage. If the Extraction Voltage rises above 10 µA constant
readback, there is excessive current leakage to ground and
indicates the source is dirty.
• Excessive leakage current can cause poor mass measurement,
unstable signals, and the risk of high voltage flash-overs in
the outer source, which could blow the emitter.
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