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Abstract: In this study, headspace single-drop microextraction (HS-SDME) coupled with gas chromatography-flame ionization detection (GC-FID), was employed to determine short-chain fatty acids (SCFAs) in ruthenium tetroxide (RuO4) oxidation products of asphaltenes. Several significant parameters, such as drop solvent type, drop volume, sample solution ionic strength, agitation speed, extraction time, and ratio of headspace volume to sample volume were optimized. Under optimum extraction conditions (i.e., a 3-μL drop of 1-butanol, 20min exposure to the headspace of a 6mL aqueous sample placed in a 10mL vial, stirring at 1000rpm at room temperature, and 30% (w/v) NaCl content), the reproducibility and accuracy of the method have been tested and found to be satisfactory. The analysis of a real asphaltene sample using this method proved that HS-SDME can be a promising tool for the determination of volatile SCFAs in complex matrices. [Copyright &y& Elsevier]

Abstract: In this study, hollow fiber based liquid-phase microextraction (HF-LPME), coupled with GC, GC–MS and GC–IRMS detections, was employed to determine petroleum hydrocarbons in spilled oils. According to the results, the HF-LPME method collected more low-molecular weight components, such as C7–C11 n-alkanes, naphthalene, and phenanthrene, than those collected in conventional liquid–liquid extraction (LLE). The results also showed that this method had no remarkable effect on the distributions of high-molecular weight compounds such as >C18 n-alkanes, C1–C3 phenanthrene, and hopanes. Also, the carbon isotopic compositions of individual n-alkanes in the two preparation processes were identical. Accordingly, HF-LPME, as a simple, fast, and inexpensive sample preparation technique, could become a promising method for the identification of oil spill sources. [Copyright &y& Elsevier]

Highlights: [•] An improved sample pre-treatment method for the analysis of SCFAs in RICO products. [•] Combine the HS-SDME with derivatization method for quantitative analysis of SCFAs in complex matrices. [•] This method allows detection of the studied analytes at low concentrations in aqueous phases. [ABSTRACT FROM AUTHOR]

• An online hydrocarbon gas concentration system is used for the intermolecular and intramolecular isotope analysis of low-abundance C 2+ gaseous hydrocarbons. • The system allows marked enrichment of low-abundance C 2+ gaseous hydrocarbons and results in no obvious isotopic fractionation. • The system coupled to GC–IRMS or GC–Py–GC–IRMS can be used for accurate and precise determination of the C–H isotopic compositions of low-content C 2+ gaseous hydrocarbons and the position-specific c isotopic compositions of low-content propane in highly mature natural and shale gases. The stable isotopic composition of natural gas can be used to identify its origin and source. However, low concentrations of gaseous hydrocarbons in high-mature natural and shale gases hinder accurate determination of their compound- and position-specific isotopic compositions. In this study, an online C 2+ hydrocarbon gas concentration system combined with gas chromatography–isotope ratio mass spectrometry (GC–IRMS) or gas chromatography–pyrolysis–gas chromatography–isotope ratio mass spectrometry (GC–Py–GC–IRMS) was developed to determine compound- and position-specific isotopic compositions of low-abundance gaseous hydrocarbons. The lower limit of the gas concentration required for isotope ratio determination using the online concentration system is 0.001% (0.003%) for compound-specific carbon (hydrogen) isotopes and 0.005% for position-specific carbon isotopes and is thus applicable to most natural gas samples. The online concentration technique does not cause significant isotopic fractionation effects, and the combination with GC–IRMS and GC–Py–GC–IRMS can accurately and precisely determine the compound-specific δ13C and δD values of low-content C 2+ gaseous hydrocarbons and the position-specific δ13C values (δ13C a , δ13C b , and SP values) of propane in low-content propane samples, respectively. The application of our method to two natural gas samples from the Ordos and Sichuan basins further confirms that the online concentration method allows simple and rapid determination of the compound- and position-specific isotopic compositions of low-abundance gaseous hydrocarbons. [ABSTRACT FROM AUTHOR]

• Deans-switch is used to avoid complex preparation and losses of trace samples. • Baseline separation of crocetane and phytane is achieved (R >1.5) by 2D-GC technique. • First accurate determination of δ13C of crocetane in natural samples by 2D-GC-IRMS. Compound-specific isotope analysis of crocetane in sediments can be used to determine its origin. However, the co-elution of crocetane with phytane and complex substrates hinders the accurate determination of its isotopic composition. A heart-cutting two-dimensional gas chromatography–isotope ratio mass spectrometry (2D-GC–IRMS) method was developed to determine δ13C values of crocetane. Full chromatographic separation of crocetane was achieved with a 30 m CycloSil-B chiral capillary first column and a 60 m Chiraldex B-pH capillary second column (two series-connected 30 m Chiraldex B-pH capillary columns). Analyses of standard mixtures confirmed that the new method has satisfactory accuracy (deviations from the authentic values <0.5‰) and precision (RSDs <5%) for carbon isotope analyses of crocetane and phytane. The application of the method to two sediment samples indicates that baseline resolution is achieved (R >1.5) for crocetane and phytane, with 13C-depleted crocetane (δ13C values of −119.5‰ and −111.5‰ in the two natural samples, respectively) being an indicator of anaerobic oxidation of methane in cold seep areas. The new 2D-GC–IRMS method allows simple and efficient determination of the compound-specific carbon isotopic compositions of crocetane. [ABSTRACT FROM AUTHOR]