Simultaneous quantification of NSO-HET markers in crude oils from different origins by GC×GC-TOFMS

Crude oils contain, in addition to conventional saturated biomarkers, nitrogen-, sulfur-, and oxygen-containing polycyclic aromatic heterocycles (NSO-HETs), including carbazoles, dibenzothiophenes, and dibenzofurans. which provide information regarding the organic matter source, depositional paleoenvironment, thermal maturity, biodegradation, and migration. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) offers high peak capacity and resolution, enabling the separation of co-eluting isomers and the simultaneous detection of multiple compound classes. This study explores the potential of the GC×GC-TOFMS technique to simultaneously quantify NSO-HET markers in a single chromatographic analysis and application to crude oil samples of different origins. Analyses were performed on a Pegasus BT4D system (LECO) coupled to a gas chromatograph (Agilent 8890), equipped with an Rxi-5MS column (30 m × 0.25 mm × 0.25 µm) in the first dimension and an NA-17 column (1.20 m × 0.25 mm × 0.25 µm) in the second dimension. The method was optimized using 53 NSO-HET analytical standards, and quantification parameters were determined. Under optimized conditions, limits of quantification ranged from 1.59 (dibenzofuran) to 41.76 (1,4-dimethyl and 3-ethylcarbazole) µg L⁻¹, within a linear range of 0.5–333.33 µg L⁻¹ for most compounds, with R² values ≥ 0,999. Application of the method to crude oils from different sources, including Recôncavo, Solimões, Santos and Sergipe Basins enabled the quantification of more than 20 NSO-HETs, including carbazoles and alkylcarbazoles; benzothiophenes, dibenzothiophenes and their alkylated homologues; and dibenzofurans, methyldibenzofurans, and benzonaphthofurans. Concentrations ranged from below the limit of quantification to 353 µg L⁻¹ for 2,7-dimethylcarbazole, with dibenzothiophene, alkylated dibenzothiophenes, and dimethylcarbazoles among the most abundant compounds. Although some isomeric pairs, including methylbenzofurans and methyldibenzofurans, remained unresolved, GC×GC-TOFMS expanded the analytical coverage compared with the previously employed targeted GC-MS/MS approach and enabled the discrimination of several positional isomers within the NSO-HET classes. The resulting quantitative profiles revealed differences in the distribution and relative abundance of NSO-HET classes and alkylated homologues among the crude oils. Therefore, GC×GC-TOFMS proved to be a powerful tool for the quantification of NSO-HET markers and for identify a large number of isomers in petroleum samples. From a geochemical perspective, the quantitative data obtained enables a new approach to interpreting organic facies and paleoenvironments for applications in petroleum system geochemistry. This quantitative approach supports the development of a model system for interpreting NSO-HET markers in geochemical studies of Brazilian sedimentary basins.