Electron Ionization (Ei) Systems; Chemical Ionization (Ci) Systems - Agilent Technologies 5975C TAD VL MSD Troubleshooting And Maintenance Manual

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Introduction

Electron Ionization (EI) systems

EI systems ionize sample molecules by bombarding them with electrons. The
ions, including fragments, are drawn into the quadrupole analyzer where they
are separated by their mass-to-charge (m/z) ratios and detected.

Chemical Ionization (CI) systems

CI systems use a reagent gas as an intermediate between the electrons and the
sample. CI is more gentle than direct electron bombardment.
The CI hardware allows the 5975 Series MSD to produce high-quality, classical
CI spectra, which include molecular adduct ions. A variety of reagent gases
can be used.
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.
16 5975 Series MSD Troubleshooting and Maintenance Manual