HP 5973 MSD Hardware Manual page 12

Description
The chemical ionization (CI) hardware allows the HP 5973 MSD to operate in the
positive and negative CI modes (PCI and NCI) and produce high-quality, classical
CI spectra, which include molecular adduct ions. A variety of reagent gases
(including methane, isobutane, and ammonia) can be used.
The HP 5973 CI system adds to the HP 5973 MSD:
• CI ion source
• Redesigned EI/CI GC/MSD interface
• Interface tip seal
• Reagent gas flow control module
• Bipolar HED power supply
• Updated GC/MSD ChemStation software
A triode high vacuum gauge controller (HP 59864B) is not included, but is
required for operation in CI mode.
To achieve the relatively high source pressure required for CI while still maintaining
high vacuum in the quadrupole and detector, the MSD CI system has been carefully
optimized. Special seals along the flow path of the reagent gas and very small
openings in the source ensure that all the source gases stay in the source long
enough for the appropriate chemical reactions to occur.
The CI interface has special plumbing for reagent gas. The interface can be used for
both EI and CI operation. A spring-loaded insulating seal fits onto the tip of the
interface to seal the opening to the ion source; this seal must be removed before
installing the EI source.
Switching back and forth between CI and EI takes less than an hour, although a
1– to 2–hour wait is required in order to purge the reagent gas lines and bake out
water and other contaminants.
The CI source, CI interface, and reagent gas control module are described in more
detail in the remainder of this chapter.
To help assure quality of reagent gas entering the system, a methane/isobutane gas
purifier is provided, and is required. It removes oxygen, water, hydrocarbons, and
sulfur compounds.
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