80 Operation Manual
4 Operating in Chemical Ionization (CI) Mode
CI Autotune
CI Autotune
After the reagent gas flow is set, the lenses and electronics of
the MS should be tuned (Table 7).
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/MS interface by means of the gas flow control
module.
There are no tune performance criteria. If CI autotune
completes, it passes.
CAUTION
Always verify MS performance in EI before switching to CI operation.
Table 7 CI tune default settings
Parameter Methane Isobutane Ammonia EI
Ion polarity Positive Negative Positive Negative Positive Negative N/A
Emission 150 A 50 A 150 A 50 A 150 A 50 A 35 A
Electron
energy
150 eV 150 eV 150 eV 150 eV 150 eV 150 eV 70 eV
Filament 1
11111 1 or 2
Repeller 3 V 3 V 3 V 3 V 3 V 3 V 30 V
Ion focus 130 V 130 V 130 V 130 V 130 V 130 V 90 V
Entrance
lens offset
20 V 20 V 20 V 20 V 20 V 20 V 25 V
Shutoff valve Open
Open Open Open Open Open Closed
Suggested
flow
20% 40% 20% 40% 20% 40% N/A
Source temp 250 °C
150 °C 250 °C 150 °C 250 °C 150 °C 230 °C
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