Bruker Daltonik GmbH
Instrument Layout
3.1.5.3 How Does LIFT Work?
LIFT consists of an arrangement of four electrodes forming three chambers, the LIFT
chamber, the Pulsed Acceleration Chamber, and the Acceleration Stage (Figure 3-9).
The LIFT device is located just behind the PCIS.
This arrangement works as follows:
Electrode No.1 and No.2 are always connected in parallel forming a cell that shields
from all external effects. Therefore the behavior of this cell can be compared with a
Faraday’s cage.
During phase 1 when the precursor and related fragments enter the first chamber the
four electrodes have the potentials as shown in Figure 3-9:
1. Electrode 1 and 2 are connected to ground.
2. Electrode 3 is connected to 19 kV.
3. Electrode 4 is always connected to ground.
Ions leave the ion source with an energy of typically 8 keV.
While the ions move inside the first cell, due to phase 2 the electrical potential of the
electrodes No.:1 and No.:2 will be raised up from ground potential to typically 19 kV.
Because there is no voltage difference and no field between both electrodes the ion
motion is influenced in no way. The particles continue moving as before however on
this increased electrical potential. This potential jump is necessary for phase 4 to take
effect.
During phase 3 the ions move from chamber 1 to chamber 2 on the raised potential.
Phase 4 begins by pulsing down the electrical potential (2 - 3kV) of electrode 3 while
precursor and related fragments are still inside cell 2. Cell 2 acts as the first (delayed)
acceleration stage. When entering cell 3 a further acceleration of the particles takes
place according to the remaining voltage difference. This pulsed extraction resembles
PIE
(chapter 3.1.4.1) and makes also use of
SVCF
(
S
pace-
V
elocity
C
orrelation
F
ocusing).
The two stage acceleration by 19 kV potential difference sufficiently increases the
kinetic energies of precursor and fragments that they are reflected properly and
directed onto the reflector detector.
Some data for illustration:
After acceleration by LIFT the energy of the parent ion is raised up to 27 keV (8KeV +
19 keV). A fragment with a molecular weight of
1
/
20
of the parent ion has got energy of
19,4 keV (
8keV
/
20
+ 19 keV). This is only about 28% less energy and allows the
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