Charge Exchange - HP 5973 MSD Hardware Manual

Charge exchange

Charge-exchange ionization can be described by the reaction:
·
+
+ M → M
X
+
where X is the ionized reagent gas, and M is the analyte of interest. Examples of
reagent gases used for charge exchange ionization include the noble gases (helium,
neon, argon, krypton, xenon, and radon,) nitrogen, carbon dioxide, carbon
monoxide, hydrogen, and other gases that do not react "chemically" with the
analyte. Each of these reagent gases, once ionized, has a recombination energy
expressed as:
·
+ –
→ X
X + e
or simply the recombination of the ionized reagent with an electron to form a
neutral species. If this energy is greater than the energy required to remove an
electron from the analyte, then the first reaction above is exothermic and
thermodynamically allowed.
Charge-exchange chemical ionization is not widely used for general analytical
applications. It can, however, be used in some cases when other chemical ionization
processes are not thermodynamically favored.
·
+
+ X
 Chemical Ionization Theory
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