Agilent Technologies 5975C TAD VL MSD Troubleshooting And Maintenance Manual page 39

High abundances at m/z 18, 28, 32, and 44 or at m/z 14 and 16
• System was recently vented (residual air and water)
• Air leak. Large peaks at m/z 14 and 16 are symptomatic of especially large
Mass assignments are incorrect
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.
• MSD has not had enough time to reach thermal equilibrium
• Large variations in the temperature of the laboratory
• MSD has not been tuned recently, or at the temperature at which it is
• Incorrect tune file (inappropriate parameters)
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 inconsistent
• MSD 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
• Electron multiplier is nearing the end of it useful lifetime
• Ground loop problems
5975 Series MSD Troubleshooting and Maintenance Manual
leaks.
operating
General Troubleshooting
2
39