## 3 Results and Discussion
In the crude oil sample, a little predominance of even over odd number of n-alkanes occurred, whereas, in the diesel samples, there was no preference for odd nor for even numbers. The C\({}_{19}\) and C\({}_{20}\) isoprenoid compounds, pristane (Pr) and phytane (Ph) have particular diagnostic value in determining the source of oil. The Pr/Ph is a very commonly used ratio in oil spill fingerprinting. Pristane and phytane peaks were observed in the region between the peaks of C\({}_{17}\) and C\({}_{18}\) n-alkanes. They were identified by their m/z 183 fragments. Moreover, in the crude oil sample, phytane was predominant over pristane, and it was definitely the most abundant compound in the whole chromatogram. The low Pr/Ph ratio is a typical characteristic of the crude oil of the Kavala basin. Contrariwise, the Pr/Ph ratio of the petroleum products was more than 1.0 (Figure 4) [15,44]. For correlations among crude oil and refined products, the m/z 191 and m/z 217 chromatograms were considered principally useful. The m/z 191 is a characteristic ion fragment of the terpen, whereas the m/z 217 is a characteristic fragment of the steranes [47]. Triterpanes and steranes are common biomarkers found in crude oils. They are considered very useful compounds for environmental forensic investigations due to their relative resistance to weathering processes [9,15]. Biomarker fingerprinting at m/z 191 (Figure 5) and 217 (Figure 6) revealed that no terpen and steranes were detected in petroleum products samples. The main characteristic found in the chromatogram of the Prinos' crude  
Figure 2: Total ion chromatogram (TIC) of (**a**) crude oil and petroleum products samples: (**b**) heating oil, (**c**) bunker oil, (**d**) diesel fuel, (**e**) gasoline, and (**f**) jet fuel. Cx = n-alkanes with x carbon atoms, C\({\rm{cxy}}\) = fatty acid methyl esters with x carbon atoms, and y unsaturation. Ph: phytane, Pr: pristane. oil was the existence of gammacerane in high concentration, which indicates a high salinity environment in the genesis of petroleum [44]. Figure 3: EIC comparison of m/z 57 between crude oil and diesel samples (heating oil, bunker oil, and diesel fuel). Figure 4: Comparison of Pr/Ph ratio between crude oil and petroleum products. Figure 5: Comparison of EIC at m/z 191 between crude oil and banker oil samples. Figure 6: Comparison of EIC at m/z 217 between crude oil and heating oil samples. Dibenzothiophene (DBT) and its derivatives comprise major polycyclic aromatic sulfur heterocyclic compounds found in crude oils and in sedimentary organic matter, providing useful information for studying petroleum correlations [48]. The identification of isomers of methyldibenzothiophene (MDBT) and isomers of dimethyldibenzothiophene (DMDBT) in crude oil was achieved by GC-MS in SIM mode at m/z 198 and 212, respectively [49]. Thus, differentiations in alkylated dibenzothiophenes between crude oil and diesel oil samples were detected at m/z 198, which is indicative of methyl-dibenzothiophenes compounds (Figure 7). Particularly, crude oil samples contained a much higher quantity of MDBT. Furthermore, results have shown that between crude oil and diesel samples, no correlation occurred comparing their EIC at m/z 212. In the case of the crude oil sample, the abundance of DMDBT was higher enough compared to the bunker oil sample (Figure 8), while in the diesel fuel sample, the dimethyl-dibenzothiophenes were totally absent (Figure 9). Figure 8: Comparison of EIC at m/z 212 between crude oil and bunker oil samples. Figure 7: Comparison of EIC at m/z 198 between crude oil and bunker oil samples. Eventually, the analysis of the TIC of the sediment and water samples clearly showed that there was no organic pollution suggesting that there was no impact from human activities on the part of the river under investigation. Moreover, no crude oil and organic toxic substances were detected from industrial waste, neither in river water nor in the river basin and seawater samples (Figure 10).