34 
Again, mass-fragment 231 may be of great help here in doubtful cases (see Paragraph 
2.2.1.2): whereas hopanes and steranes may show arbitrary mixtures of the clusters of the 
individual products, the aromatic steranes are much more interesting. Because they solely 
originate from the HFO in HFO-/lubricating oil mixtures they appear on top of the 4-alpha- 
steranes, which originate mainly from the lubricating oil (Figure 30 lower chromatograms). 
Fig. 30: Mass-chromatograms of mass-fragment 231 of the bunker- and sludge-samples of 
Figure 26.