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Theory and Inner Workings
Sample Ionization Technology
Sample Ionization Technology
Electrion Impact Ionization
LE-EI Ion Source
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In GC/MS, before the sample can be analyzed, it must be ionized
in the ion source. There are two primary methods of ionization
in GC/MS: electron impact (EI) ionization, and chemical
ionization (CI). The 7250 Q-TOF at this time supports only an EI
source.
In electron impact ionization mode, the sample stream enters
an EI ion source from the GC/MS interface. Electrons emitted
from a filament located in the ionization chamber, are guided by
a magnetic field axially along with the ion beam. The
high-energy electrons interact with the sample molecules,
ionizing and fragmenting them. The positive voltage on the
repeller pushes the positive ions into the lens stack, where they
pass through several electrostatic lenses. These lenses
concentrate the ions into a tight beam, which is directed into
the quadrupole mass filter.
The 7250 Q-TOF ion source has two modes of ionization, 70 eV
for classical fragment libraries and 15 eV for low energy
ionization.
The 7250 Q-TOF uses the an improved version of the new high
efficiency ionization source (HES) first used in the Agilent
single and triple quadrupole mass spectrometers.
Agilent's HES technology provides a greater than 10 to 20 fold
increase in ion creation relative to sources that ionize
compounds in a orthogonal plane to the ion beam.
Sample ions enter the source through the GC/MS interface. The
sample is ionized in the ionization chamber which is made up of
the source body, repeller, and filament block containing the
filament and a focusing lens.
Agilent 7250 Q-TOF GC/MS Concepts Guide
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