Operating in Electron Impact (EI) Mode 3
5975 Series MSD Operation Manual for MassHunter 73
The largest influence on operating pressure in EI mode is the carrier gas
(column) flow. Table 13 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 MassHunter Data Acquisition software for information on
troubleshooting air leaks and other vacuum problems.
In the Instrument Control view you can set up an MS Monitor for displaying this
vacuum reading. The vacuum can also be read on the LCP or from the Manual
Tune screen.
Table 13 Ion vacuum gauge reading
Column flow rate,
mL/min
Gauge reading, Torr
Performance turbo
pump
Gauge reading, Torr
Standard turbo pump
Gauge reading, Torr
Diffusion pump
Foreline reading, Torr
Diffusion pump
0.5 3.18E–06 1.3E–06 2.18E–05 34.7
0.7 4.42E–06 1.83E–06 2.59E–05 39.4
1 6.26E–06 2.61E–06 3.66E–05 52.86
1.2 7.33E–06 3.11E–06 4.46E–05 60.866
2 1.24E–05 5.25E–05 7.33E–05 91.784
3 1.86E–05 8.01E–05 1.13E–04 125.76
4 2.48E–05
6 3.75E–05
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