Agilent Technologies G7035A, Operation Manual

Page: 104 / 172

104 5977 Series MSD Operation Manual
4
Operating in Chemical Ionization (CI) Mode
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 positive chemical ionization
(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 ion source, perform the standard autotune, save the report, and
note the reported pressure. See
“To Tune the MSD in EI Mode” on page 69.
2
Vent the system. See “Venting the MSD” on page 57.
3
Install the CI ion source. See “To Install the CI Ion Source” on page 167.
4
Pump out the system. See “To Pump Down the MSD in CI Mode” on
page 98.
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 117.
6
Select
Bake out MSD
from the
Manual Tune
view
Execute
menu to display the
Specify Bake Out parameters
dialog. Set for 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 MassHunter 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.
C A U T I O N
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
.