7 CI Maintenance
198 5977B Series MSD Operating Manual
General Information
Ion source cleaning
The main effect of operating the MSD in CI mode is the need for more frequent
ion source cleaning. In CI operation, the ion source chamber is subject to more
rapid contamination than in EI operation because of the higher source
pressures required for CI.
Ammonia
Ammonia, used as a reagent gas, increases the need for foreline pump
maintenance. Ammonia causes foreline pump oil to break down more quickly.
Therefore, the oil in the standard foreline vacuum pump must be checked and
replaced more frequently.
Always purge the MSD with methane after using ammonia.
Be sure to install the ammonia with the tank in an upright position. This will
help prevent liquid ammonia from getting into the flow module.
To set up your MSD for CI operation
Setting up your MSD for operation in CI mode requires special care to avoid
contamination and air leaks.
Guidelines
• Before venting in EI mode for the installation of the CI source, verify that
the GC/MSD system is performing correctly. (See “To Verify EI System
Performance” on page 108.)
• Make sure the reagent gas inlet line(s) are equipped with gas purifiers (not
applicable for ammonia).
• Use extra-high purity reagent gases; 99.99% or better for methane and as
pure as is available for other reagent gases.
Always perform any maintenance procedures using hazardous solvents under a
fume hood. Be sure to operate the MSD in a well-ventilated room.
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