9780521516358book.pdf

atoms (such as Ar, He, Xe) of high velocity. A later development was the use of a beam of

caesium (Csþ)ionsandthetermliquid secondary ion mass spectrometry(LSIMS) was

introduced to distinguish this from FAB–MS.Pseudomolecular ion speciesarise as either

protonated or deprotonated entities (MþH)þand (MH)respectively, which allows

15

27

32

41

42

43

28

29

58

% relative abundance

(b)

10

0

20 30 40 50 60

10

20

30

40

50

60

70

80

90

100

m/z

(a) CH 3 CH 2 CH 2 CH 3

CH 3 CH 2 CH 2 CH 3 ¬+.

+e–

CH 3 CH 2 CH 2. + CH 3.

CH 3 CH 2. + CH 3 CH 2 ¬+

¬+

CH 2 ¬+

CH¬+

C¬+

m/z=15

m/z = 29

CH 2 CH¬+

m/z= 27

CH 3 ¬+

m/z= 15

CH 2 ¬+

m/z= 14

CH 3 CH 2 ¬+

m/z= 29

CH 3 CHCH¬+

¬+

m/z= 41

m/z= 43

etc. etc.

CH 3 + CH 3 CH 2 CH 2

Fig. 9.3Fragmentation pathways inn-butane and the EI spectrum. The pathway for fragmentation of

n-butane is shown in (a) and the EI spectrum in (b). In the spectrum, the relative abundance is plotted

from 0 to 100% where the largest peak is set at 100% (base peak). Spectra represented in this way are

said to benormalised.

357 9.2 Ionisation