18 5975 Series MSD Operation Manual for MassHunter
1 Introduction
In this manual, the term “CI MSD” refers to the G3174A MSD and upgraded
G3172A MSDs. It also applies, unless otherwise specified, to the flow modules
for these instruments.
The 5975 Series CI system adds to the 5975 Series MSD:
• EI/CI GC/MSD interface
• CI ion source and interface tip seal
• Reagent gas flow control module
• 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 (G3397A) is required for CI MSD and is
recommended for EI also.
The MSD CI system has been optimized to achieve the relatively high 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 tip of the interface.
Switching back and forth between CI and EI sources takes less than an hour,
although 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 about
2 hours for the ion source to cool.
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