80
3 CI Troubleshooting
Excessive noise or low signal-to-noise ratio
The GC inlet needs maintenance.
Refer to the GC manual.
The CI ion source is dirty.
Clean the ion source.
Poor vacuum
Check the pressure on the high vacuum gauge controller.
Air leak
Run Methane Pretune (in PCI). A large peak at m/z 32 indicates air in the
system. Check for, and correct any leaks. See the Leaks section at the
beginning of this chapter.
Saturated methane/isobutane gas purifier
Replace the gas purifier.
Poor quality methane (purity below 99.99%)
Replace the methane with high-purity methane. If necessary, clean and purge
the reagent gas lines and clean the ion source.
Reagent gas flows too high (in EI/PCI MSDs)
Verify that the reagent gas setup is correct.
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