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NOTE: Reagent ion formation can be a complex process. For example, for
proton transfer CI with methane used as the reagent gas, reagent gas ions are
formed as follows:
First, methane is ionized to form two primary ions:
CH
4
+ e- (CH
4
)
+
+ 2 e
-
CH
4
+ e- CH
3
+
+ e- + H
-
These primary ions then react very rapidly to form predominantly the secondary
ions,
CH
5
+
and C
2
H
5
+
:
(CH
4
)
+
+ CH
4
CH
5
+
+ CH
3
CH
3
+
+ CH
4
C
2
H
5
+
+ H
2
The CI Parameters
Reagent Gas
When you select a standard reagent gas (i.e., methane, isobutane, acetonitrile or
ammonia), the CI parameters for the selected gas are set automatically, and you
do not need to change the default values of the CI parameters. Be aware that if
you do change a CI parameter and set it incorrectly, you may not be able to
operate properly in CI. However, the CI parameters: Max. Ion Time, Max. React
Time, CI Storage Level Ejection Amplitude (v), and Background Mass can be
varied to optimize for sensitivity.
CI Storage level
CI Storage level is the value of the smallest mass stored in the ion trap during
the ionization of the reagent gas and the lowest mass stored during the reaction
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