5 Operating in EI Mode
To Monitor High Vacuum Pressure
126 5977B Series MSD Operating Manual
The largest influence on operating pressure in EI mode is the carrier gas
(column) flow. Table 10 lists typical pressures for various helium carrier
gas flows. These pressures are approximate and will vary from instrument
to instrument by as much as 30%.
If the pressure is consistently higher than those listed, refer to the online help in
the Agilent MassHunter GC/MS Acquisition software for information on
troubleshooting air leaks and other vacuum problems.
In the Instrument Control view, you can set up an MSD Monitor for displaying this
vacuum reading. The vacuum can also be read on the 8890 or 7890 Series GC
control panel or from the Manual Tune screen.
Table 10 Ion vacuum gauge reading
Column flow rate,
mL/min
Optional gauge
reading, Torr
Turbo pump
Gauge reading, Torr
Diffusion pump
Foreline reading,
mTorr
Diffusion pump
0.5 3.18E–06 2.18E–05 34.7
0.7 4.42E–06 2.59E–05 39.4
1 6.26E–06 3.66E–05 52.86
1.2 7.33E–06 4.46E–05 60.866
2 1.24E–05 7.33E–05 91.784
3 1.86E–05 1.13E–04 125.76
42.48E–05
63.75E–05
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