Agilent Technologies 5975T LTM GC/MSD, Руководство по устранению неисправностей и техническому обслуживанию

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56 Troubleshooting and Maintenance Guide
3
Chromatographic Symptoms
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 operating
• 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 empty or almost empty
• Calibration valve not working correctly
• Dirty ion source
• Electron multiplier is nearing the end of it useful lifetime
• Ground loop problems
Relative abundance of m/z 502 is less than 3%
Autotune should give an m/z 502 relative abundance greater
than 3%. The relative abundance of m/z 502 can, however, vary a
great deal depending on column flow, ion source temperature,
and other variables. As long as relative abundance is above 3%,
the stability of the relative abundance is more important than
the absolute value. If you observe significant changes in the