50 Troubleshooting and Maintenance Manual
3 CI Troubleshooting
Common CI-Specific Problems
Because of the added complexity of the parts required for CI, there are many
potential problems added. By far the greatest number and most serious
problems with CI are associated with leaks or contamination in the reagent
gas introduction system. NCI is especially sensitive to the presence of air;
leaks small enough to cause no problems in PCI can destroy NCI sensitivity.
As with EI, if the MS tunes well and no air leak is present, sample sensitivity
problems should be addressed by GC inlet maintenance first.
• Wrong reagent gas
• Reagent gas not hooked up or hooked up to wrong reagent gas inlet port
• Wrong ions entered in tune file
• Wrong tune file selected
• Not enough bakeout time has elapsed since vent (background is too high)
• Wrong column positioning (extending > 4-5 mm past tip of interface)
• Interface tip seal not installed
• EI source installed in CI mode
• EI filament or other EI source parts in CI ion source
• Air leaks in reagent gas flow path
• CI filament has stretched and sagged:
• High emission current
• High temperature
• Filament was defective
• Linear (no inflection point) electron energy (EIEnrgy) ramp
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