| Nowadays, oil spills have become a global problem, causing both immediate and long-term environmental damages. The identification of spilled oils is highly important for environmental damage assessments. In this study, some typical oils including crude oils from China’s offshore areas and imported crude oils were selected as the research objects to develop gas chromatography-mass spectroscopy method for identification and characterization of these polycyclic aromatic sulfur heterocycles (PASHs) and diamondoid compounds in these oils. Based on different composition and distribution characteristics of crude oils from different sources, new biomarkers reflecting oil intrinsic features were found in this study. Furthermore, the effects of natural weathering on alteration of distribution of PASHs and diamondoid compounds were investigated and traceable biomarkers that are resistant to weathering were selected. This study provides theoretical foundation and key technology for developing new techniques of oil spill identification and improving the accuracy of oil spill pollution sources discrimination.First, the application of micro-solid-phase extraction for sample cleanup with gas chromatography-mass spectrometry in the determination of petroleum hydrocarbons in crude oils is reported. Silica gel was selected as the adsorbent (20 mg). Aliphatic fraction was eluted using 70μL hexane and aromatic fraction was eluted with 90μL mixed solution (hexane:dichloromethane (1:1, vol/vol). The recoveries are within the range of 80.74～112.5%; and the relative standard deviation values of all analytes from five replicate injections are better than 6.32%, indicating the good recovery and precision of the method.Second, a simple and rapid solid-phase microextraction approach for the isolation of PASHs from the aromatic fraction of crude oil is described.8-hydroxyquinoline silica gel impregnated with palladium chloride was used as a sorbent material for extraction. The developed methodology was tested in the characterization of crude oils samples collected at different oil fields and fuel oil samples. The total concentration of PASHs ranged from 140.06μg/g to 51422.88μg/g in crude oil samples and from 1416.44μg/g to 5461.63μg/g in fuel oil samples. Generally, the abundances of PASHs in crude oils follow a increasing order of the hero beach of Zhanhua, Bohai Sea, Weizhou island and imported crude oils.Thirdly, a semiquantitative gas chromatography-mass spectrometry method for analysis of diamondoid compounds in crude oils and oil products collected from various sources is reported. Based on the chromatograms properties and the calculated retention indices,26 diamondoid compounds were analyzed qualitatively and the semiquantitative concentration formula using the internal standard were provided. The concentrations of adamantanes are in the range of approximately 46.45μg/g to 2085.39μg/g in crude oils and 23.37 to 652.57μg/g in fuel oils. The abundance of adamantanes is higher than diamantanes accounting for more than 65 percent of diamondoids (except for crude oil from the hero beach of Zhanhua). Crude oils from different offshore oil platform but the same block exhibit very similar diamondiod signatures, in contrast, oils from different sources have different signatures of both the concentrations and relative distribution patterns of diamondoid compounds.Fourthly, a number of diagnostic ratios of PASHs and diamondoids have been development and assessed as source indicators using their diagnostic powers. Forty one crude oil samples and six fuel oil samples were identified on the basis of 13 diagnostic ratios of PASHs and 25 diagnostic ratios of diamondoid compounds using principle component analysis (PCA). The 13 diagnostic ratios of PASHs were the first key factor for fuel oil classification, and the 25 diagnostic ratios of diamondoid were the second one for crude oil. Diagnostic ratios based on PASHs and diamondoid compounds coupled with PCA could be used to identify large numbers of crude oil and fuel oil.At last, the changes of PASHs and diamondoid compounds in the crude oil from Bohai sea and fuel oil sample during natural long-term weathering (0～100 days) were presented. The results showed that the distribution patterns of dibenzothiophene compounds in crude oil remained relatively stable after 100 days natural weathering, the distribution pattern of benzo[b]naphtho[1,2-d]thiophene had slightly change after 100 days weathering. The 13 diagnostic ratios of PASHs are relatively stable in 60 days natural weathering. The customary five diagnostic ratios were proved to have strong weathering-resistant capabilities under natural weathering conditions and they can be used for source identification of weathered oil (60～100 days). The concentrations of diamantanes slightly decrease with an increase of weathering time and diamantanes have stronger weathering-resistant capabilities. According to the "Student’s t" test, nine ratios of diamantanes had no apparent changes which could indicate the source of the samples during 20 days weathering. Diamantanes ratios of DMDI-4 and DMDI-5 are essentially unaltered after 100 days natural weathering which could indicate the source of the samples during natural long-term weathering. |
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