Agilent Technologies 7000 Triple Quadrupole GC/MS, Maintenance Manual

Page: 36 / 214

36 Troubleshooting and Maintenance Manual
2
General Troubleshooting
•
Electron multiplier is nearing the end of it useful lifetime
• Ground loop problems
Relative abundance of m/z 502 is low or nonexistent
Autotune should give an m/z relative abundance greater than 1%. 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 1%, the stability of relative abundance is more important
than the absolute value. If you observe significant changes in the relative
abundance of
m/z 502 for a fixed set of operating parameters, there may be a
problem.
Low
relative
abundance of
m/z
502 should not be confused with low
absolute
abundances at high masses. Sensitivity at high masses can be excellent even if
the relative abundance of
m/z
502 is near 1%. If your MS produces low absolute
abundances at high masses, refer to the symptom “High mass sensitivity is
poor” on page 37
.
Manual tune programs (not autotune) may have different relative abundances.
• Tune program file has different relative ion source default values
• Not enough time for the MS to warm up and pump down
• Analyzer chamber pressure is too high
• Ion source temperature is too high
• Column carrier gas flow is too high
• Poor filament operation
• Dirty ion source
• Air leak
• Incorrect DC polarity on the quadrupole mass filter
Spectra look different from those acquired with other MSs
Ion ratios are different from those in older models MSs. This is due to the HED
detector and the type of MS being compared, and is normal. Single quadrupole
and triple quadrupole spectra will look different.