Installation manual

Operating in Chemical Ionization (CI) Mode 4
5975 Series MSD Operation Manual 109
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 Select Gas A. Follow the instructions and prompts from the Tune Wizard.
2 Set the flow to 20% for PCI/NCI MSDs.
3 Check the vacuum gauge controller to verify correct pressure. See page 124.
4 Select Methane Pretune from the Setup menu.
The methane pretune tunes the instrument for optimum monitoring of the
ratio of methane reagent ions m/z 28/27.
5 Examine the displayed profile scan of the reagent ions (Figure 29).
• Make sure there is no visible peak at m/z 32. A peak there indicates an
air leak. If such a peak is present, find and repair the leak before
proceeding. Operating in the CI mode with an air leak will rapidly
contaminate the ion source.
• Make sure that the peak at m/z 19 (protonated water) is less than 50% of
the peak at m/z 17.
6 Perform the Methane Flow Adjust.
CAUTION
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.