23 
2.3.1.2 GC-MS analysis 
Cracking processes lead to distinct clusters of isomers. The cluster of isomeric M- 
phenanthrenes, for example, is typical of the high-temperature production of aromatics 
(Figure 17). It is generally found, e.g., in soot particles of diesel exhaust gases. Retene is not 
present (Figure 18) because aromatics with slightly longer side chains are not produced in 
higher-temperature processes. 
Fig. 17: Mass-chromatograms of mass 192 (M-phenanthrenes, M-anthracene) of HFOs (same 
samples as in Fig. 14). 
Fig. 18: Mass-chromatograms of mass 234 (tetra-M-phenanthrenes, M- benzo-naphtho- 
thiophenes) of HFOs (same samples as in Fig. 14).