Bruker Daltonik GmbH
Instrument Layout
3.1.5.2 LIFT
To understand TOF MS/MS, first it has to be realized that parent ions and fragments
formed in the drift region, travel side by side with the same velocity through the TOF.
Molecules break after acceleration in the source, since the kinetic energy release is
only a few eV. Thus fragments have smaller kinetic energy than parents (E
kin
~m). Our
gridless reflector can focus in time and space about 30% of difference in kinetic energy,
e.g., from the parent down to fragments with 70% of the parent mass. Ions with less
energy do not hit the detector. To obtain a full MS/MS spectrum the reflector voltage
has to be stepped down as known for segmented PSD or FAST (Figure 3-7).
P
2
+
Target
Reflector Reflector
plate detector
L
inear
d
etec
tor
Drift region
P
1
+
PCIS
/
IS2
G
round
po
te
nt
ia
l
P
1
+
P
1
+
Parents and
fragments
IS
1
IS
1
Figure 3-7 Principle of a conventional PSD measurement
The basic idea of LIFT is to raise the kinetic energies of parent (Ps
+
) and fragment ions
(F
+
) to a level that the energy difference between parent and smallest fragment does
not exceed 30% (Figure 3-9). In that case all the fragments can be simultaneously
detected with the parent ion (Figure 3-8).
The
Pre Cursor Ion Selector
(PCIS) is able to pick a parent with the associated
fragments out of a mixture, e.g., a digest (chapter 3.1.5.1), as fragments that are
produced before arriving at the PCIS assembly pass the unit together with the parent
because of their same velocity. .
ultraflex III User Manual, Version 1.0
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