90 5977 Series MSD Operation Manual
4 Operating in Chemical Ionization (CI) Mode
General Guidelines
• Always use the highest purity methane (and other reagent gases, if
applicable). Methane must be at least 99.9995% pure.
• Always verify the MSD is performing well in EI mode before switching to CI.
See “To Verify System Performance” on page 71.
• Make sure the CI ion source and GC/MSD interface tip seal are installed.
• Make sure the reagent gas plumbing has no air leaks. This is determined in
PCI mode, checking for m/z 32 after the methane pretune.
• Make sure the reagent gas inlet line is equipped with gas purifiers (not
applicable for ammonia).
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