Caracterização geoquímica de óleos do Brasil e do México através de biomarcadores moleculares usuais e não usuais por cromatografia gasosa bidimensional abrangente acoplada por espectrometria de massas por tempo de voo

Abstract

Comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GCxGC - TOFMS), currently one of the most powerful analytical tools that can separate mixtures at a high resolution, was used to characterize hydrocarbons in oils from Brazil and Mexico. The biomarker parameters, which are typically used to predict the organic matter input, paleoenvironmental conditions and thermal maturity of the oils, were calculated using the GCxGC - TOFMS data. According to the ratios, Mexican samples are associated with anoxic environment and Brazilian samples with oxic conditions. Regarding to the Peters and Moldowan scale, only the CAC-CAM sample is biodegraded (level 5). Besides the usual biomarkers, the technique allowed for the identification of unusual compounds such as 2αmethylhopanes, 8,14-seco-hopanes, 8,14-secomoretanes and several ring-A methyl sterane series, including 2α, 3β e 4α-methyl steranes (C22 and C28–C31) and dinosteranes. 8,14 secohopanes, 8,14 secomoretanes (C33), and ring A methyl steranes (C22 and C31) were identified for the first time in Brazilian oils. The 4α-methyl and 4,23,24-trimethyl steroids can be related to dinoflagellate organic matter and abundant dinosteranes suggesting dinoflagellate blooms during source rock deposition. Furthermore, C22 short-chain steranes indicated organic matter deposited under hypersaline, marine carbonate or sulfur-rich depositional conditions. These results indicate the efficiency of GCxGC - TOFMS as a technique for separation and identification of biomarkers in oils.