6 Operating in CI Mode
CI Autotune
5977B Series MSD Operating Manual 145
CI Autotune
After the reagent gas flow is adjusted, the lenses and electronics of the MSD
should be tuned. (See Table 11 on page 146.)
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.
EMV at or above 2600 V, however, indicates a problem. If your method requires
EMV set at +400, you may not have adequate sensitivity in your data acquisition.
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.
Always verify MSD performance in EI before switching to CI operation. (See
“To Verify EI System Performance” on page 131.) Always set up the CI MSD in
PCI first, even if you are going to run NCI.
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