Linear
detectorReflector detectorIon gate(b) In the linear mode Reflector+
- (^0) +
Ion gate
0
(c) In the PSD mode
0 + +
(^0) +
+^0
Voltage gradient
(a)
Fig. 9.16The MALDI–TOF reflector. Post-source decay (PSD) theory. (a) Fragment ions arising by PSD as well
as the neutral fragments and the precursor ions have the same velocity and reach the detector simultaneously.
This prevents a distinction between precursor and PSD fragment. (b) In the linear mode the charged fragments
are not separated. (c) In the reflector mode, the fragment that does not retain the charge (neutral, denoted
by 0) is not deflected in the reflector but the charged fragments (þ) are deflected according to theirm/z
and a spectrum of the fragment (daughter) ions is recorded, albeit of a limitedm/zrange for each setting
of the reflector voltages.
Ions of same mass but different velocities
+20 kV field applied
0V Flight tube
Sample on target plate Detector
+20 kV field
1
2
3
Fig. 9.15Delayed extraction (DE). (1) No applied electric field. The ions spread out. (2) Field applied. The
potential gradient accelerates slow ions more than fast ones. (3) Slow ions catch up with faster ones at the
detector.
374 Mass spectrometric techniques