Hybrid Configuration CI
When the 4000 MS is in Hybrid Configuration, the CI reagent gas (from an
external gas cylinder) enters the external ion source through a length of restrictor
tubing. In standard Hybrid High Pressure Source (HPS) Configuration, a high
pressure CI volume is automatically inserted into the EI volume to create a high-
pressure environment to enhance CI reactions. The reagent gas is ionized by EI
to form reagent ions. Both positive and negative ions may be formed in these
processes and reagent ions of either positive or negative charge are transferred
immediately to the ion trap. The polarity of ions carried into the ion trap for
analysis depend upon whether the user has specified to perform positive or
negative CI in the 4000 MS Method section.
Once reagent ions have been stored in the ion trap for the designated ion time,
waveforms are applied to isolate only the reagent ions within a mass range
designated in the 4000 MS Method. Finally, the chosen reagent ions react with
neutral analytes entering the ion trap through the GC column.
An additional Liquid CI Inlet (or LCI Inlet) option allows the selection of certain
liquids as sources for CI. A 200 mL/min restrictor is used for admitting reagent
through the Liquid CI Inlet when one is in Hybrid Configuration. The operation of
this option and switching between Liquid and Gaseous CI is described later in
this section.
Installing CI Reagent Gas
We recommend that the inlet gas line be as short as possible. Ideally you should
secure the gas cylinder close to the rear of the 4000 MS so that the 4 mL/min
restrictor tube can be attached by a 1/8” Swagelok fitting directly to the two-stage
gas regulator and the other end of the restrictor attached through the CI Gas inlet
into the MS. Make sure, however, that the gas line is long enough to run to the
rear of the 4000 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 4000 MS system for leaks
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