HP 5973 MSD, Hardware Manual

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54
CI operation
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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 ion mode (PCI). 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 to 20%, pre-tuning 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.
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Gas A
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Gas A
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Methane Pretune
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The methane pretune tunes the instrument for optimum monitoring of the methane
reagent ion
m/z 28/27 ratio.
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• 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 not larger than the peak
at m/z 17.
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Adjust the methane flow to get the ratio of m/z 28:27 between 1.5 and 5.0.
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.
C A U T I O N 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 will need to
vent the MSD
and
clean the ion source
.