Agilent Technologies 5975 Operation Manual page 188

A
Chemical Ionization Theory
Dissociative electron capture
Dissociative electron capture is also known as dissociative resonance capture.
It is a process similar to electron capture. The difference is that during the
reaction, the sample molecule fragments or dissociates. The result is typically
an anion and a neutral radical. Dissociative electron capture is illustrated by
the reaction equation:
This reaction does not yield the same sensitivity as electron capture, and the
mass spectra generated typically have lower abundance of the molecular ion.
As with electron capture, the products of dissociative electron capture are not
always stable. The reverse reaction sometimes occurs. This reverse reaction is
sometimes called an associative detachment reaction. The equation for the
reverse reaction is:
Ion pair formation
Ion pair formation is superficially similar to dissociative electron capture. The
ion pair formation reaction is represented by the equation:
As with dissociative electron capture, the sample molecule fragments. Unlike
dissociative electron capture however, the electron is not captured by the
fragments. Instead, the sample molecule fragments in such a way that the
electrons are distributed unevenly and positive and negative ions are
generated.
188
 M
MX + e –
(thermal)
·
 MX + e –
–
M + X
M
MX + e –
(thermal)
·
–
+ X
+ + X¯ + e –
5975 Series MSD Operation Manual for MassHunter