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Chemical Ionization Options
Chemical Ionization Options
Introduction
Chemical ionization (CI) provides mass spectral data that complement electron
ionization (EI) data for the analysis of complex compounds. In the standard CI
mode of operation, a CI reagent gas is introduced into the ion trap analyzer from
an external gas supply cylinder. The reagent gas is ionized by EI to form reagent
ions. These reagent ions then ionize sample molecules entering the ion trap with
He carrier gas from the capillary column. The operation and adjustment of
reagent gases for the standard CI option are described in the first part of this
section.
NOTE: The CI mode is an option on the Saturn GC/MS. If your system does not
have this option, you will not be able to perform CI analyses.
Two additional options allow the selection of certain liquids as sources for CI
reagent. These are the Liquid CI Inlet (or LCI Inlet) and the Multiple CI Module
(or MCI Module). The installation and operation of these options is described
later in this section.
Installing CI Reagent Gas
Before evacuation, new gas lines will contain a significant amount of adsorbed
water vapor. The longer the gas line, the greater the amount of adsorbed water
and the greater the pumping time required to evacuate water from the line. To
minimize the pumping time required to evacuate the gas line, we recommend
that the line be as short as possible. Make sure, however, that the gas line is
long enough to run to the rear of the Saturn GC/MS and to accommodate the
movement of the mass spectrometer 9 inches (23 cm) to the right (for access to
the transfer line and turbomolecular pump).
Gas cylinders or lecture bottles should not be stored where they can damage
cables or gas lines, and they should be secured in accordance with standard
safety practices. Lecture bottles have rounded ends and will require some
means of support (e.g., Matheson Model 505 Non-Tip Stand).
Before installing the CI reagent gas supply, you should complete the following
procedures:
•
Tune the instrument in EI mode
•
Check the Saturn GC/MS system for leaks
