## 3 Results and Discussion  
Identification of petroleum hydrocarbons and differentiation between crude oil and petroleum products were based on the total ion chromatographs (TICs) (Figure 2) and the extracted ion chromatographs (EICs) of the examining water and sediment samples [42]. Specifically, the following structural features were examined thoroughly by GC-MS:  
* The shape of chromatograms conforming to the standards peaks;
* The ratio between n-alkanes with even and odd numbers of carbon atoms;
* The ratio between phytane and pristine;
* The presence of parent and alkylated PAHs;
* The presence of alkyl-substituted and unsubstituted aromatic hydrocarbons;
* The presence of sulfur heterocyclic aromatic compounds. The refined petroleum products, such as heating oil, bunker oil, diesel fuel, gasoline, jet fuel, etc., may diverge in the carbon range, the hydrocarbon distribution pattern, and unresolved complex mixture (UCM) profile due to the various feedstocks of crude oil used in their production process [43]. Figure 2a illustrates the total ion chromatogram of the crude oil sample obtained from Prinos oilfield. It is dominated by even-numbered carbon atoms in a carbon range between C\({}_{11}\)-C\({}_{34}\), which probably indicates anoxic, hyperasaline depositional environment. Moreover, the relatively low concentrations of n-alkanes in the carbon range between C\({}_{21}\)-C\({}_{35}\) indicate additional evidence of marine origin [44]. The peaks of isoalkanes, cycloalkanes, and aromatic hydrocarbons appeared among peaks of n-alkanes with a lower intensity. The refined petroleum products are differentiated by the presence and concentration of the n-alkane peaks. After the C\({}_{27}\) peak, n-alkanes were only present in the crude oil samples. In the heating oil (Figure 2b), the most abundant identified n-alkanes were C\({}_{17}\) and C\({}_{19}\), while in the bunker oil (Figure 2c), the distribution was more bell-shaped with a prevalence of C\({}_{14}\) and C\({}_{16}\). In the diesel fuel sample (Figure 2d), maxima were observed from nC\({}_{14}\) to nC\({}_{17}\), as well as peaks from fatty acid methyl esters (FAMEs) denoting the presence of biodiesel [45]. Figure 2: _Cont._  
There were apparent differentiations in the chromatogram comparison of gasoline (Figure 2e) and jet fuel (Figure 2f) samples with crude oil and diesel oil samples, respectively. The chromatograms of gasoline and jet fuel illustrated peaks only within the C\({}_{9}\)-C\({}_{12}\) window of n-alkanes. Gasoline as a light petroleum cut presents light-end, resolved hydrocarbons with very slight UCM content. The identification of gasoline in the environment is hard enough as volatile hydrocarbons evaporate rapidly. After leaving the spiked samples with gasoline for three days at room temperature, the chromatograms of the spiked samples revealed significant differences from the original samples with obvious evaporation of most gasoline components. Hence, the identification of gasoline is usually based on the detection of characteristic compounds, which are used as additives, such as methyl tert-butyl ether (MTBE) [46]. On the other hand, the TIC of the jet fuel sample (Figure 2f) was characterized by an abundance of aromatic compounds, such as C\({}_{3}\) and C\({}_{4}\) alkyl benzenes, and the presence of naphthalene, 1- and 2-methylnaphthalene, and indane. EICs provided higher discrimination capacity among samples than TICs. The comparison of the EICs at m/z 57 (Figure 3) indicated a clear diversity in the occurrence of n-alkanes, isoprenoid alkanes, and mid-chain methylalkanes in samples. The n-alkanes of the diesel samples (heating oil, bunker oil, and diesel fuel) were distributed in a carbon range from n-C\({}_{11}\) to n-C\({}_{27}\), much narrower than the carbon range of crude oil sample from n-C\({}_{11}\) to n-C\({}_{34}\). Low molecular weight hydrocarbons (<n-C\({}_{11}\)) were evaporated under experimental conditions.