Installation manual

118 5975 Series MSD Operation Manual
4 Operating in Chemical Ionization (CI) Mode
To perform a PCI autotune (methane only)
Procedure
1 Verify that the MSD performs correctly in EI mode first. See page 76.
2 Load the PCICH4.U tune file (or an existing tune file for the reagent gas you
are using).
If you use an existing tune file, be sure to save it with a new name if you
don’t want to overwrite the existing values.
3 Accept the default settings.
4 Perform methane setup. See page 109.
5 Under the Tune menu, click CI Autotune.
There are no tune performance criteria. If autotune completes, it passes
(Figure 30). If the tune sets the electron multiplier voltage (EMVolts) at or
above 2600 V, however, you may not be able to acquire data successfully if your
method sets EMVolts to “+400” or higher.
The autotune report contains information about air and water in the system.
The 19/29 ratio shows the abundance of water.
The 32/29 ratio shows the abundance of oxygen.
CAUTION
Always verify MSD performance in EI before switching to CI operation. See page 76.
Always set up the CI MSD in PCI first, even if you are going to run NCI.
CAUTION
Avoid tuning more often than is absolutely necessary; this will minimize PFDTD
background noise and help prevent ion source contamination.