General Troubleshooting 2
Troubleshooting and Maintenance Manual 35
High background
• Pressure in the analyzer chamber is too high
• Air leak
• Contamination
Mass assignments are incorrect (scan mode only)
Small shape changes at the top of the mass peaks can cause 0.1 m/z shifts in
mass assignments. Shifts greater than 0.2 m/z indicate a possible malfunction.
• MS has not had enough time to reach thermal equilibrium
• Large variations in the temperature of the laboratory
• MS has not been tuned recently or at the temperature at which it is
operating
• Incorrect tune file (inappropriate parameters)
• No voltage to extractor lens (if using extractor EI source)
Peaks have precursors
The tune report lists the size of the precursors for the tune masses. Small
precursors are not unusual. If the precursors are unacceptably large for your
application, one of the following may be responsible:
• Repeller voltage is too high
• Peaks are too wide
• Incorrect DC polarity on the quadrupole mass filter
• Dirty quadrupole mass filter
Peak widths are very low
• MS has not had enough time to reach thermal equilibrium
• Large variations in the temperature of the laboratory
• Incorrect tuning
• Calibration vial(s) empty or almost empty
• Calibration valve(s) not working correctly
• Dirty ion source
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