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9.3.9 Delayed extraction

In the first MALDI–TOF instruments, the ions in the plume of material generated by

the laser pulse were continuously extracted by a high electrostatic field. Since this

plume of material occupies a small but finite volume of space, ions arising at different

1 Samples on

target plate

2 Camera

Vacuum

pump

Vacuum

pump

Linear

detector

Reflector detector

Flight tube Ion gate

3 Laser

pulses

Reflector

Grids

Voltage

gradient

7 Data system

4

56

Fig. 9.12MALDI–TOF instrument components. (1) Sample mixed with matrix is dried on the target plate which

is introduced into high-vacuum chamber. (2) The camera allows viewing of the position of the laser beam which

can be tracked to optimise the signal. (3) The sample/matrix is irradiated with laser pulses. (4) The clock is

started to measure time-of-flight. (5) Ions are accelerated by the electric field to the same kinetic energy and are

separated according to mass as they fly through the flight tube. (6) Ions strike the detector either in linear

(dashed arrow) or reflectron (full arrows) mode at different times, depending on theirm/zratio. (7) A data

system controls instrument parameters, acquires signal versus time and processes the data.

% Intensity

10

20

30

40

50

60

70

80

90

100

Mass (m/z) Mass (m/z)

1874.9790

1193.7027

1692.2220

1037.5707 1434.8363 1783.8597

1703.9316

1329.7604

1168.6175

1169.6206

1170.6269

1171.6166

1172.6194

1179.6641

Fig. 9.13Two examples of MALDI–TOF peptide spectra. The left-hand spectrum is from a protein digest

mixture and the right-hand image is an expanded one of a small part of a spectrum showing^13 C-containing

forms (see Section 9.5.4).

369 9.3 Mass analysers