Excursus: Rules for initial mass spectrum interpretation
Considering the summarized aspects of ab initio mass spectra interpretation
leads to the following simple procedure:
1. Try to identify the molecular ion and examine its intensity
2. Check for the nitrogen rule
3. Identify aliphatic and aromatic pattern
4. Search for significant ion series (e.g. m/z 57, 71, 85 . . .)
5. Identify isotope pattern (S, Cl, Br)
6. Examine the more significant fragments and consider possible hetero atom
induced cleavages
Approaches to interpret a mass spectrum
Molecular ion
Pattern
Even
Uneven
but even fragments
N-rule
Aliphatic pattern
Aromatic pattern
Isotope pattern
Composition of the fragments
Consider bond breaks near heteroatoms
Significant ion series
50
100
150
200
250
m/z
rel. intensity
121
137
193
249
Sn
Tributyl methyl tin
isotope pattern of
tin
Fig. 5.12 Mass spectrum of biomethylated tributyl tin indicating the unique tin isotope pattern
visible in the various fragments
112
5 GC/MS Data Evaluation