1. Ionization techniques, Mass spectra and MS-Instrumentation
Molecule ionization methods:
Electron impact (EI) and Chemical ionization (CE)
(GC-MS)
Electro spray ionization (ESI)
(LC-ESI-MS)
Matrix assisted laser desorption (MALDI)

3. Agilent GC-MS

4. M + e-  M+. + 2e-

5. Electron impact ionization (EI)
ABC + e-  ABC e e eV Molecular ion (1 eV) 55 eV eV
ABC+.  AB+ + C.
ABC+.  A. + BC+
AB  A B+
Mass spectrum

6. Aromatic ketones

8. Mass Analyzers Quadrupole Ion trap Magnetic Sector Linear Ion trap
Time of Flight (TOF)
Fourier Transform (FTMS)
Types of mass analyzers in current use for desktop and research LC/MS systems.

11. Molecular weight (MW) g/mol
Determination of Bruttoformulars from precise Mass determination (Excact mass)
Molecular formular
Molecular weight (MW) g/mol
Precise Mass
C3H8O
60.1
C2H8N2
C2H4O2
C4N2O
Precise Mass (C3H8O) = 3× × =

12. Molecular Mass and Nominal Mass
Atomic mass Br:
79Br (50.69%) m = Da
81Br (49.31%) m = Da
Atomic mass Br = * * = Da
1 Da = 1/12 of the mass of 12C isotope.
The nominal mass of a molecule or ion is the integer
mass of the species with the most abundant isotope
of the constituent atoms
Nominal mass of Br = 79

14. Number of C = 100×[M+1]/([M]×1.1)

17. Nitrogen rule
If a compound contains an even number (0, 2, 4…) of nitrogen atoms, its molecular ion will be an even mass number.
An odd number (1, 3, 5 ..) of nitrogen atoms => The mass number of M+. will be odd.

18. Basic advices Identify the mole peak M+.
Nitogen rule: Determine number of N
A+2 elements: Cl, Br, S, Si
NC = 100×[M+1]/([M]×1.1)
Determine brutto formular
Calculate r + db = NC – NH/2 + NN/2 + 1
(halogens counts as H)

19. Stevensons rule
The most probable fragmentation is the one that leaves the positive charge on the fragment with the lowest ionization energy
H3C+ < RCH2+ < R2CH+ < H2C=CH-CH2+ < C6H6CH2+
Difficult Easy

21. Ionization mechanisms in EI mass spectrometry
Four mechanisms:
s a b rH

22. s - cleavage

23. a-cleavage

24. a cleavage of alcohols

25. a-cleavage

26. b-cleavage

27. rH : McLafferty rearangement

31. Heptadecanoic acid methyl ester

32. Ionization techniques, Mass spectra and MS-Instrumentation
Molecule ionization methods:
Electron impact (EI) and Chemical ionization (CE)
(GC-MS)
Electro spray ionization (ESI)
(LC-ESI-MS)