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4
Operating in Chemical Ionization (CI) Mode
3
4
The flow control module
The CI reagent gas flow control module regulates the flow of reagent gas into
the CI GC/MSD interface. The flow module consists of a mass flow controller
(MFC), gas select valves, CI calibration valve, shutoff valve, control electronics,
and plumbing. See
The back panel provides Swagelok inlet fittings for methane (CH4) and one
OTHER reagent gas. The software refers to them as Gas A and Gas B,
respectively. If you are not using a second reagent gas, cap the OTHER fitting to
prevent accidental admission of air to the analyzer. Supply reagent gases at
25 to 30 psi (170 to 205 kPa).
The shutoff valve prevents contamination of the flow control module by
atmosphere while the MSD is vented or by PFTBA during EI operation.
102
Enter the reagent gas flow setpoint in the Flow field. This value is entered
as a percentage of maximum flow rate. The recommended flow is 20% for a
PCI source and 40% for an NCI source.
The flow control hardware remembers the flow setting for each gas. When
either gas is selected, the control board automatically sets the same flow
that was used for that gas the last time.
To begin reagent gas flow, select Shutoff Valve.
The system turns off the present gas flow while leaving the shutoff valve
(Figure 16
on page 103) open. This is to remove any residual gas in the
lines. Typical evacuation time is 6 minutes and then the shutoff valve is
closed.
Figure 16
and
Table 18
on
page
5977 Series MSD Operation Manual
103.
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