| With the rapid development of economic globalization and the uneven distribution of oil resources, petroleum exploration, mining and transportation scale unceasingly expands, and meanwhile more oil spill accidents ocurr day by day, such as oil-well-blowout , oil pipeline rupture, shipping oil leakage, etc. which brings us the problems of environmental assessment and of disputes caused by oil spill.Oil fingerprint analysis and identification can do us a lot of favor such as helping (1) assess the impact of oil spill on the environment through studying on oil weathering and degradation process, (2) assess the degree of the impact which the spill oil gives the environment through oil component analysis and biotoxic experiment, (3) provide scientific basis for the investigation and handling of oil accidents, including finding the oil resources and oil types, narrowing the scope of investigation objects, and make sure the troublemaker。The issues we face in oil spill identification include: (1) There are too lack information of the scope of semi-quantification, even though we all know its advantage is saving time, effort, and money. (2) There are two standard state-methods to measure petroleum hydrocarbons in samples, which based on the instruments of UV and GC-MS. However, such cases we may have experienced, the UV method give us a concentration, which may passed the limit to the environment, but GC-MS gives nothing, which means there are no hydrocarbons in the sample. (3) It is about the identification of mixed oils. Now, the articles in public give such a clue: the spill-oil identification procedure and most oil chemical fingerprint study aim at one-oil type or one oil type component contributes far more than the other oil spill cases. So how to face the identification of mixed-oil spill type and to calculate the ratio of its component and to fix this kind job sucessfully is almost a blind field.This article aims to find the answer to solve the issues the third paragraph described, the findings are as belows,(1) The two diagnostic area ratios of C17/Pr and C18/Ph increase with the concentration of the four hydrocarbons which form the ratios of C17/Pr and of C18/Ph, while area ratios of Pr/Ph, CPI, (C19+C20)/(C21+C22) and of (C21+C22)/(C28+C29) decrease in the same time. Notice that when the concentration of each of this four hydrocarbons belows 5 ofμg/ml, all the diagnostic area ratios changes sharply with the concentration.(2) The area ratio of (C21+C22)/(C28+C29) can not be used because of it changes sharply with the concentration of its four components, but the area ratios of Pr/Ph, of CPI and of (C19+C20)/(C21+C22) are recommended.(3) When the concentration of the standard-oil belows 6.3 ofμg/ml that measured by UV (equals to 129 ofμg/L of the oil in water sample in GB-1997 and 258 ofμg/L of the oil in water sample in GB-2007), GC-MS can just give a no-peak chromatogram, and if the concentration of the standard-oil belows 12.1 ofμg/ml that measured by UV (equals to 242 ofμg/L of the oil in water sample in GB-1997 and 484 ofμg/L of the oil in water sample in GB-2007), GC-MS cannot measure the concentration of the samples'constitutes.(4) There are not only physical changes occur during the process of two oil samples mixed, but also chemical changes are, and through the process the already exist difference of the diagnostic ratios between each oil sample before mixed may be enlarged, which may be important to the identification of mixed oil.(5) There are still the possibility that two oil samples are not identical even after all the diagnostic ratios of n-alkanes and the specific information about terpanes give us this clue. So, in order to do oil identification sucessfully, one should check as much as possible specific information. |
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