6
Operating in CI Mode
High Vacuum Pressure in CI Mode
132
7000/7010 Series TQ GC/MS Operating Manual
High Vacuum Pressure in CI Mode
The largest influences on operating pressure in CI mode are the reagent and CC
gas flows.
lists typical pressures for various reagent gas flows,
depending upon the CC gas flowrate. Familiarize yourself with the
measurements on
your
system under operating conditions, and watch for
changes
that may indicate a vacuum or gas flow problem. Measurements will
vary by as much as 30% from one MS to the next.
Analyzer vacuum with reagent gas flowing
Note that the MFC is calibrated for methane and the vacuum gauge is calibrated
for nitrogen, so these measurements are not accurate, but are intended as a
guide to typical observed readings. (See
.) They were taken with the
following set of conditions. Note that these are typical PCI temperatures:
Source temperature
300 °C
Front quad temperature
150 °C
Rear quad temperature
150 °C
Interface temperature
280 °C to 320 °C
Helium carrier gas flow
1 mL/min
Table 10 Typical analyzer vacuum with reagent gas flow
CC gas flow on
N
2
= 1.5, He = 2.25
CC gas flow off
MFC (%)
Rough vac
High vac
Rough vac
High vac
10
1.77
×
10
–1
7.15
×
10
–5
1.33
×
10
–1
2.56
×
10
–6
15
1.86
×
10
–1
7.19
×
10
–5
1.43
×
10
–1
3.00
×
10
–6
20
1.94
×
10
–1
7.23
×
10
–5
1.53
×
10
–1
3.45
×
10
–6
25
2.02
×
10
–1
7.27
×
10
–5
1.63
×
10
–1
3.86
×
10
–6
30
2.10
×
1
–1
7.31
×
10
–5
1.71
×
1
–1
4.30
×
10
–6
35
2.18
×
10
–1
7.39
×
10
–5
1.80
×
10
–1
4.76
×
10
–6
40
2.25
×
10
–1
7.43
×
10
–5
1.88
×
10
–1
5.18
×
10
–6