6 Operating in CI Mode
To Set Up Methane Reagent Gas Flow
154 5977B Series MSD Operating Manual
To Set Up Methane Reagent Gas Flow
The reagent gas flow must be adjusted for maximum stability before tuning the
CI system. Do the initial setup with methane in PCI mode. No flow adjustment
procedure is available for NCI, as no negative reagent ions are formed.
Adjusting the methane reagent gas flow is a three-step process: setting the flow
control, pretuning on the reagent gas ions, and adjusting the flow for stable
reagent ion ratios, for methane, m/z 28/27.
Your data system will prompt you through the flow adjustment procedure.
Procedure
1 Using an EI source, perform the standard autotune, save the report, and note
the reported pressure. (See “To Tune the MSD in EI Mode” on page 127.)
2 Vent the system. (See “To Vent the MSD” on page 136.)
3 Install the CI source. (See “To Install the CI Source” on page 250.)
4 Pump out the system. (See “To Pumpdown the MSD in CI Mode” on
page 148.)
5 Wait until the pressure is near the previously recorded pressure for the EI
autotune. (See “To Monitor CI Mode High Vacuum Pressure” on page 165.)
6 Select Bake out MSD from the Manual Tune view in the Execute menu to
display the Specify Bake Out parameters dialog. Set a minimum time of
2 hours, adjust the other parameters, and click OK to begin the bake out.
7 Select Methane Pretune from the Setup menu and follow the system
prompts. See the Agilent MassHunter GC/MS Acquisition software online
help for additional information.
The methane pretune tunes the instrument for optimum monitoring of the
ratio of methane reagent ions m/z 28/27.
After the system has been switched from EI to CI mode, or vented for any other
reason, the MSD must be baked out for at least 2 hours before tuning.
Continuing with CI autotune if the MSD has an air leak or large amounts of
water will result in severe ion source contamination. If this happens, you need
to vent the MSD and clean the ion source.
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