Rapid hydrocarbon group-type semi-quantification in crude oils by comprehensive two-dimensional gas chromatography

Petroleum is the main source of energy used in the world. The oil industry faces challenges in trying to understand the chemical composition of crude oils, quantitatively and qualitatively. The application of specific and sophisticated techniques allows a detailed characterization and provides important information that impacts from the exploration to production, transportation, and crude oil refining. A set of twelve crude oil samples with different API gravity were analyzed via comprehensive two-dimensional (2D) gas chromatography coupled to time-of-flight mass spectrometry (GCxGC-TOFMS) aimed at the detection, identification and semi-quantification of hydrocarbon classes using extracted ion chromatogram (EIC) and total ion chromatogram (TIC). The use of the polar/non-polar column configuration provided better separation between the hydrocarbon classes which allowed the identification and semi-quantification of the same. Therefore, series of n- and iso-alkanes, alkyl-cyclohexanes, alkyl-cyclopentanes, alkyl-decalines, alkyl-naphthalenes, alkyl-phenanthrenes and alkyl-9H-fluorenes were characterized. In the present study, a semi-quantification approach to data assessment using TIC is proposed. Comprehensive evaluation provided the chromatographic fingerprint of each sample in a single analysis followed by the semi-quantification of the hydrocarbon classes. The oil samples presented completely different hydrocarbon class data, even when presenting similar API gravity values. Branched alkanes and n-alkanes were the major semi-quantified compounds, and branched alkane concentrations were higher than n-alkanes in the majority of samples. These results afford valuable information for the petrochemical industry. GCxGC-TOFMS was applied for speciation and group-type semi-quantification using a single oil drop without a fractionation or clean up step.