38 
Oil Spill Identification - Round Robin 20045 
Spill II vs. PRP source oils 
Figure 5. Comparison of absolute differences between DRs of Spill-II and Souree-I and Souree-II 
with the corresponding CrDs based on the repeatability limit. 
Fig 13: 
Ratio differences (NERI) 
The use of a fix RSD overcomes this situation. 
NFI calculates ratios from a series of PAH's and biomarkers. The ratios 
shown in fig 14 have been normalized on the ratio's of Source I. 
Fig 14 
The stable PAH ratios of the four 
samples (in duplicate), normalized on 
the ratio's of Source l (NFI) 
Because Extract I and II are prepared from Source I all ratios 
theoretically should have the value of 1. In practice the analytical 
method causes small differences. As a numerical limit 10% lines are