14 
Fig. 7: Comparison of mass-chromatograms 234 (above) and 240 of a fresh (left) and a highly 
weathered light fuel oil (same samples as in Fig. 5). 
Because of the complexity of these chromatograms, one rarely finds any compounds that are 
suitable for calculating ratios. But, as always when complexity increases, much more 
information is revealed to the human eye than can be converted into suitable numbers. 
Depending on the individual case, i.e. on the particular type of light fuel oil in the spill sample 
and its degree of weathering, additional parameters that are useful for the verification of 
results can be found. In the mass chromatogram of mass 220, for example, TM- 
phenanthrenes appear together with benzo-naphtho-thiophene. 
In case the spill sample is only slightly weathered, mass 184 allows a direct comparison of 
tetra-M-naphthalenes with dibenzo-thiophene. But it must be kept in mind here that this 
particular relation may have been influenced not only by evaporation of the lower-boiling 
naphthalenes but also by possible solution of dibenzo-thiophene in water. 
2.2 Lubricating oil 
Commonly used lubricating oils consist mainly of the residues from atmospheric crude oil 
distillation, which are further distilled under vacuum conditions to produce a range of vacuum 
distillates. Solvent extraction and/or hydrofining are then used to increase the viscosity index, 
enhance the colour and convert undesirable chemical structures such as unsaturated 
hydrocarbons and aromatics to less chemically reactive species. Finally, solvent dewaxing is