Polycyclic aromatic hydrocarbons contents during the Triassic–Jurassic Boundary transition in the Haojiagou section, Junggar Basin, Northwest China

Seventy samples were collected from Beds 39 to 54 in the Haojiagou section, Junggar Basin, Northwest China. To minimize contamination and the effects of oxidation, the samples were stored in plastic bags, and any weathered surfaces or veins were removed. Subsequently, the samples were ultrasonically cleaned three times with distilled water and dried at 55oC for 24 hours. All analyses were conducted at the State Key Laboratory of Petroleum Resource and Engineering, China University of Petroleum (Beijing). Approximately 100 g of crushed sample was Soxhlet-extracted with dichloromethane in a 60 oC water bath for at least 8 h. The extract was dissolved in petroleum ether to precipitate and remove asphaltenes through filtration. A chromatography column packed with a silica gel/alumina (3:2), with a small plug of degreased cotton at its base, was used to isolate aromatic hydrocarbons. The aromatic fraction was eluted with petroleum ether/dichloromethane (2:1, v/v). After the fraction separation, the aromatic hydrocarbons were transferred to sample vials. The deuterated phenanthrene (D10-Phe, m/z 188) was used as the internal standard. The aromatic hydrocarbon fractions were investigated by Agilent 7890B Gas Chromatograph and 5977 Mass Spectrometry (GC-MS) equipped with an HP-5 MS fused silica column (60 m×0.25 mm×0.25 μm). The injection temperature was set to 300oC, with helium (He) as the carrier gas at a flow rate of 1.0 mL/min. The injection mode was splitless. The initial oven temperature was 80oC, and then the oven temperature increased at 3oC /min to 310oC, and finally held constant for 16 min. The scan range was m/z 50 to 450, and the detection mode was full scan. The mass spectrometer was operated using electron impact (EI) ionization at 70 eV. Data acquisition was performed simultaneously in both full scan and selected ion monitoring (SIM) modes. Subsequently, qualitative and quantitative analyses of the data were carried out using Agilent’s Data Analysis software. In the DATA mode, biomarkers were identified by comparing their molecular weights, characteristic ion peaks, and retention times with the spectral database. In the DATA SIM mode, the peak areas of biomarkers were exported. Based on the concentration of the internal standard and its peak area, the biomarker concentrations were obtained. The results are shown in Table S1.