Operating in Chemical Ionization (CI) Mode 4
5977 Series MSD Operation Manual 93
CI Autotune
After the reagent gas flow is adjusted, the lenses and electronics of the MSD
should be tuned. See “Reagent gas settings” on page 94.
Perfluoro-5,8-dimethyl-3,6,9-trioxidodecane (PFDTD) is used as the calibrant.
Instead of flooding the entire vacuum chamber, the PFDTD is introduced
directly into the ionization chamber through the GC/MSD interface by means
of the gas flow control module.
There is a PCI autotune for methane only, as there are no PFDTD ions
produced by other gases in positive mode. PFDTD ions are visible in NCI for
any reagent gas. Always tune for methane PCI first, regardless of which mode
or reagent gas you wish to use for your analysis.
There are no tune performance criteria. If CI autotune completes, it passes.
EMVolts (electron multiplier voltage) at or above 2600 V, however, indicates a
problem. If your method requires EMVolts set at +400, you may not have
adequate sensitivity in your data acquisition.
CAUTION
After the source is changed from EI to CI or vented for any other reason, the MSD must
be purged and baked out for at least 2 hours before tuning. Longer bakeout is
recommended before running samples requiring optimal sensitivity.
CAUTION
Always verify MSD performance in EI before switching to CI operation. See “To Verify
System Performance” on page 71. Always set up the CI MSD in PCI first, even if you are
going to run NCI.
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