Inner Workings – Triple Quadrupole MS versus Single Quadrupole MS 2
How a single quadrupole mass spectrometer works
Agilent 6400 Series Triple Quad LC/MS Concepts Guide 19
What about fragment ions?
Full scans with a single quadrupole instrument can also be used
to study fragment ions. See Figure 5.
Figure 5 Fragment ions with single quadrupole MS
The diagram shows that fragment ions, also known as product
ions, are formed by fragmenting or breaking apart precursor
ions. Precursor ions formed in the ion source travel through the
mass analyzer without change, unless extra energy is applied to
their motion in a region where fragmentation can occur.
This fragmentation or collisionally induced dissociation (CID)
can be carried out in a low pressure region between the ion
source and the mass analyzer. The ion source is under
atmospheric pressure, while the mass analyzer is at a much
lower pressure because it has been evacuated of gas with
a vacuum pump.
On the Agilent single quadrupole mass spectrometer, this region
is between the capillary exit and the skimmer, where the gas
pressure is about 2 Torr, or about three orders of magnitude
below atmosphere pressure (760 Torr). Under normal
operation, a voltage is applied across this region to keep the
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