6 Operating in CI Mode
To Operate the CI MSD
5977B Series MSD Operating Manual 147
To Operate the CI MSD
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. (See Table 12.)
Start the system in PCI mode
By bringing the system up in PCI mode first, you will be able to do the following:
• Set up the MSD with methane first, even if you are going to use another
reagent gas.
• Check the interface tip seal by looking at the m/z 28 to 27 ratio (in the
methane flow adjust panel).
• Determine if a gross air leak is present by monitoring the ions at m/z 19
(protonated water) and 32.
• Confirm that the MSD 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. 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.
Depending upon the application, use the following reagent gas flow rates during
system startup:
• PCI mode set reagent gas flow to 20 (1 mL/min)
• NCI mode set reagent gas flow to 40 (2 mL/min)
Table 12 Temperatures for CI operation
Ion source Quadrupole GC/MSD interface
PCI 250 °C 150 °C 280 °C
NCI 150 °C 150 °C 280 °C
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