HP 5973 MSD, Hardware Manual

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CI operation
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51
CI operation
Operating your MSD in the CI mode is slightly more complicated than operating in
the EI mode. After tuning, gas flow, source temperature, and electron energy may
need to be optimized for your specific analyte.
General guidelines
• Make sure the CI ion source and GC/MSD interface tip seal are installed.
• Make sure the reagent gas plumbing has no air leaks. This is determined in PCI
mode, checking for
m/z 32 after the methane pre-tune.
• Set ion source temperature to 150°C for negative CI, and 250°C for PCI. Set
quadrupole temperature to 106°C for both modes.
• Set the GC/MSD interface temperature to 320°C for PCI, and 280°C for NCI.
Start the system in PCI mode first.
By bringing the system up in PCI mode first, you will be able to do the following:
• Check the interface tip seal by looking at the
m/z
28 to 27 ratio (in the methane
flow adjust panel.).
• Tell if a gross air leak is present by monitoring the ions at m/z 19(water), 32.
• Confirm if the MS is generating “real” ions and not just background noise.
It is nearly impossible to perform any diagnostics on the system in NCI. In NCI, there
are no reagent gas ions to monitor for any gas. It is difficult to diagnose an air leak
and difficult to tell whether a good seal is being created between the interface and
the ion volume.