1 Introduction
20 5977B Series MSD Operating Manual
In this manual, the term “CI MSD” refers to the G7078B MSD or to the G7077B,
G7079B, and G7081B models that were field upgraded for CI operation. It also
applies, unless otherwise specified, to the flow modules for these instruments.
The CI hardware upgrade allows the MSD to produce high-quality, classical
CI spectra, which include molecular adduct ions. A variety of reagent gases
can be used. (See Chapter 5, “Operating in CI Mode” on page 119.)
The 5977B Series CI system field upgrade adds the following to the 5977B
Series MSD:
• EI/CI GC/MSD interface
• JetClean option that shares the same MFC system EI/CI GC/MSD interface
• CI source with the new common interface tip seal that can also be used
with an EI XTR source or HES
• Reagent gas MFC
• Bipolar HED power supply for PCI and NCI operation
A methane/isobutane gas purifier is provided and is required. It removes
oxygen, water, hydrocarbons, and sulfur compounds.
A high vacuum gauge controller (G3397B) is integrated in the system. Its use is
required for CI, and it is recommended for EI also.
The CI system has been optimized to achieve the relatively high CI source
pressure required for CI while still maintaining high vacuum in the
quadrupole and detector. Special seals along the flow path of the reagent gas
and very small openings in the ion source keep the source gases in the
ionization volume long enough for the appropriate reactions to occur.
The CI interface has special plumbing for reagent gas. A spring-loaded
insulating seal fits onto the end of the GC/MSD interface.
Switching back and forth between CI and EI sources takes less than an hour,
however, a 1- to 2-hour wait is required to purge the reagent gas lines and bake
out water and other contaminants. Switching from PCI to NCI requires
approximately 2 hours for the ion source to cool.
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