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Chemical Ionization Options
If you are planning to use a different CI reagent in each Channel of the MCI
Module, save a unique GC/MS Method specific to each Channel of the MCI,
each with External Events programming of the correct Event.
Under Saturn 2000 Mass Spec Control choose the Method Directory item MS
Method Editor to prepare a CI/MS section of the Method.
Several parameters must be examined or selected for an appropriate acquisition
with a given CI reagent.
In this example, note that the low mass limit for acquisition is 70 and the
Background Mass is set to 65 for the acetonitrile CI method. Collecting data
below this limit might result in significant interferences from acetonitrile reagent
ions. Similar parameters for isobutane CI are advised. Acquisitions with
methanol, ammonia, and methane reagents can generally be accomplished
effectively with lower starting ranges and background masses. See the tables
Default Parameters for Liquid CI Reagents
or
Default Parameters for
Gaseous CI Reagents
for suggested background masses. Low mass for
acquisition should never be lower than the suggested background mass for a
given reagent.
Also note that the mode for acquisition must be changed from EI Auto to CI Auto.
Save the GC/MS Method with a name indicating the CI reagent chosen - in this
case we save the method as ACN_CI.mth If you are planning to use a different
CI reagent in each Channel of the MCI Module, save a unique GC/MS Method
specific to each Channel of the MCI, each with External Events programming of
the correct Event.
GC/MS SampleList for Alternating EI/MS and CI/MS
Acquisitions
In this example, a set of three samples has been placed in the 8200
AutoSampler in positions 1, 2, and 3 of the sample carousel. When the
AutoSampler run is started, each sample will first be run in EI mode using the
method EI_GC.mth, then in CI mode with acetonitrile as the CI reagent using the
method ACN_CI.mth. Note that care must be taken to use the correct GC/MS
method for each entry in the table. The data can now be acquired in automation
by preparing appropriate SampleList for the 8200 AutoSampler, the 3800 GC and
the Saturn MS.
