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3 CI Troubleshooting
Reagent gas ion ratio is difficult to adjust or unstable
The interface tip seal is incorrectly placed, damaged, or missing.
Inspect the Isolation tip. If necessary, remove and reinstall it to ensure a good
seal with the CI ion source. Replace it if it is damaged. Install it if it is missing.
Residual air and water in the MSD or in the reagent gas supply lines
Run the methane pretune. Air will appear as a peak at m/z 32 and excessive
water as a peak at m/z 19 > m/z 17. If either of these conditions is present,
purge the reagent gas supply lines and bake out the MSD. See “To Clean the
Reagent Gas Supply Lines” on page 149. Continued presence of a large peak at
m/z 32 may indicate an air leak. After correcting the problems, you may need
to clean the ion source.
Air leak
Run Methane Pretune (in PCI). Large peak at m/z 32 indicates air in the
system. Check for and correct any leaks. See “Air Leaks” on page 66.
The reagent gas supply is at the wrong pressure.
Check the regulator on the reagent gas supply. It should be adjusted to 20 psi
(140 kPa).
A leak in the reagent gas delivery path.
This is especially likely if you have set the methane flow much higher than
normal and the ratio is still too low.
Check the reagent gas path. Tighten fittings.
The CI ion source is dirty.
Clean the ion source.
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