Maxim V Giruts
Gubkin Russian State University of Oil and Gas, Russia
Maxim V Giruts is from Gubkin Russian State University of Oil and Gas, Russia.
Diamondoids has a characteristic mass-spectra using a gas chromatography-mass spectrometry (GC-MS) for their analysis. Their characteristic ions are m/z 136, 135, 149, 163, 177 (for adamantanes C10-C14), m/z 188, 187, 201 (for diamantanes C14-C16), m/z 240, 239 (for triamantanes C18-C19) and m/z 292 (for tetramantanes C22). At the same time our investigations have been shown that often there are many foreign peaks at the diamondoids mass-chromatograms. These foreign peaks elute together with diamondoids at the same retention time. Since there is no published data on the diamondoids retention indices the correct identification of these hydrocarbons is difficult. At present time adamantanes and diamantanes are more studied than triamantanes and tetramantanes. It can be possible because their relative concentrations in crude oils are considerably higher than triamantanes and tetramantanes ones. As has been mentioned above triamantanes and tetramantanes are less studied than adamantanes and diamantanes. Nevertheless despite the presence of many foreign peaks at the m/z 240, 239, 292 and 291 mass-chromatograms we recently identified triamantanes and tetramantanes. For this purpose we used method of thermal-diffusion separation of saturated fractions of oils and isomerization of saturated concentrates with alumosilica catalyst. We determined the retention indices of triamantane (C18), 9-methyltriamantane (C19) and all isomers of tetramantane (C22) (iso-, anti- and skew-). The report will present their masschromatograms. Distribution of triamantanes and tetramantanes in crude oils studied poorly but we have found that their distribution in oils of various genotypes are different. Thus distribution of triamantanes and tetramantane can be used like admantane, diamantane and triamantane in geochemical investigations. According to our studies the distribution of C10-C22 diamondoids can be used for correlations biodegradated and unbiodegradated crude oils.