4 Operating in EI Mode
To Monitor High Vacuum Pressure
5977C GC/MSD Operating Manual 99
The largest influence on operating pressure in EI mode is the carrier gas
(column) flow. Table 9 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 9000 Series GC
touchscreen or from the Manual Tune screen.
Table 9 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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