Inner Workings – Triple Quadrupole MS versus Single Quadrupole MS 2
How a triple quadrupole mass spectrometer works
Agilent 6400 Series Triple Quad LC/MS Concepts Guide 29
In this example, a precursor ion is selected using the first
quadrupole and is sent to the collision cell for fragmentation.
The fragments are scanned through the third quadrupole
resulting in a product-ion scan MS/MS. Since the fragment ions
are pieces of the precursor, they represent portions of the
overall structure of the precursor molecule. A triple quadrupole
instrument can be used in this way to identify a compound’s
fingerprint.
A full scan MS/MS using a triple quadrupole MS is also not the
most sensitive mode for the same reason that a full scan MS
using a single quadrupole is not the most sensitive mode of
operation possible (first belt remains steady; second belt
moves). The most sensitive mode of operation for the triple
quadrupole MS instrument is to fix both belts and only monitor
a specific precursor ion and a specific product ion. This mode is
called selected reaction monitoring or SRM.
In normal operation, a triple quadrupole MS instrument
involves running multiple SRMs for the same precursor ions.
This is called multiple reaction monitoring or MRM.
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