Shukui Zhu

Screening of oil sources by using comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry and multivariate statistical analysis.

Using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC×GC/TOFMS), volatile and semi-volatile organic compounds in crude oil samples from different reservoirs or regions were analyzed for the development of a molecular fingerprint database. Based on the GC×GC/TOFMS fingerprints of crude oils, principal component analysis (PCA) and cluster analysis were used to distinguish the oil sources and find biomarkers. As a supervised technique, the geological characteristics of crude oils, including thermal maturity, sedimentary environment etc., are assigned to the principal components. The results show that tri-aromatic steroid (TAS) series are the suitable marker compounds in crude oils for the oil screening, and the relative abundances of individual TAS compounds have excellent correlation with oil sources. In order to correct the effects of some other external factors except oil sources, the variables were defined as the content ratio of some target compounds and 13 parameters were proposed for the screening of oil sources. With the developed model, the crude oils were easily discriminated, and the result is in good agreement with the practical geological setting.

Predictions of comprehensive two-dimensional gas chromatography separations from isothermal data

Two-dimensional retention times and peak widths in temperature programmed comprehensive two-dimensional gas chromatography were predicted using a theoretical model developed from experimental data obtained under isothermal conditions. A Matlab program was written to calculate the following parameters: dead time (t(M)), elution temperature (T(e)), retention time (t(R)), hold-up width (w(M)) and peak width (w(R)). The two-dimensional retention times of a sample mixture that contained n-alkanes and polyaromatic hydrocarbons (PAHs) were predicted and were observed to be in excellent agreement with experimentally determined values. The relative deviation between the model and the experimental data was less than 2 and 7% for the primary and secondary retention times, respectively. The relative deviation of peak width was less than 7 and 10% in the primary and secondary dimensions, respectively. The advantage of this model was its simplicity, informed entirely from experimental data, with no reliance on theoretical parameters. This prediction model would be useful for optimizing GC×GC separation conditions and for confirming compound identifications of components that are chromatographically resolved but that have nearly identical mass spectra.

A micro-solid phase extraction in glass pipette packed with amino-functionalized silica for rapid analysis of petroleum acids in crude oils

In this work, a micro-solid phase extraction (micro-SPE) method was developed for the analysis of petroleum acids in crude oils. Plastic vessels were found to be unsuitable as the micro-SPE vessel, because of the plasticizer interferences and the serious adhesion of oil samples on vessel surfaces. To reduce or eliminate these influences, a glass pipette was selected as the micro-SPE vessel. With the glass pipette micro-SPE format, amino-functionalized silica was chosen as the sorbent for extraction of petroleum acids based on mix-mode hydrogen bonding/ion-exchange interactions. The conditions of the micro-SPE were carefully optimized. Under the optimized conditions, no evaporation was needed, which can save time and reduce losses of analytes. By coupling with gas chromatography-mass spectrometry (GC-MS), the proposed micro-SPE method for analysis of petroleum acids was proved to be easily operated, fast (the micro-SPE can be accomplished within 5 min), solvent-saving (3 mL of solvent), reproducible and sensitive (the limits of detection range from 2 ng g−1 to 6 ng g−1).

Determination of diamondoids in crude oils using gas purge microsyringe extraction with comprehensive two dimensional gas chromatography-time-of-flight mass spectrometry.

Based on a homemade device, gas purge microsyringe extraction (GP-MSE) of crude oil samples was developed for the first time. As a simple, fast, low-cost, sensitive and solvent-saving technique, GP-MSE provides some outstanding advantages over the widely used sample preparation methods for crude oils such as column chromatography (ASTM D2549). Several parameters affecting extraction efficiency were optimized, including extraction temperature, extraction time, extraction solvent, condensing temperature and purge gas flow rate. With the optimized GP-MSE conditions, several real crude oil samples were extracted, and trace diamondoids were determined using comprehensive two dimensional gas chromatography-time-of-flight mass spectrometry (GC×GC-TOFMS). In total, more than 100 diamondoids were detected and 27 marker compounds were identified and quantified accurately. The limits of detection (LODs, S/N=3) were less than 0.08μg/L for all diamondoids. The relative standard deviation (RSD) was below 8%, ranging from 1.1 to 7.6%. The linearity of the developed method was in the range of 0.5-100.0μg/L with correlation coefficients (R2) more than 0.996. The recoveries obtained at spiking 50μg/L were between 81 and 108% for diamondoids in crude oil samples. The developed method can also be extended to the analysis of other components in crude oils and other complex matrices.

Porphyrin-based magnetic nanocomposites for efficient extraction of polycyclic aromatic hydrocarbons from water samples

Stable and reusable porphyrin-based magnetic nanocomposites were successfully synthesized for efficient extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental water samples. Meso-Tetra (4-carboxyphenyl) porphyrin (TCPP), a kind of porphyrin, can connect the copolymer after amidation and was linked to Fe3O4@SiO2 magnetic nanospheres via cross-coupling. Several characteristic techniques such as field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, vibrating sample magnetometry and a tensiometer were used to characterize the as-synthesized materials. The structure of the copolymer was similar to that of graphene, possessing sp2-conjugated carbon rings, but with an appropriate amount of delocalized π-electrons giving rise to the higher extraction efficiency for heavy PAHs without sacrificing the performance in the extraction of light PAHs. Six extraction parameters, including the TCPP:Fe3O4@SiO2 (m:m) ratio, the amount of adsorbents, the type of desorption solvent, the desorption solvent volume, the adsorption time and the desorption time, were investigated. After the optimization of extraction conditions, a comparison of the extraction efficiency of Fe3O4@SiO2-TCPP and Fe3O4@SiO2@GO was carried out. The adsorption mechanism of TCPP to PAHs was studied by first-principles density functional theory (DFT) calculations. Combining experimental and calculated results, it was shown that the π-π stacking interaction was the main adsorption mechanism of TCPP for PAHs and that the amount of delocalized π-electrons plays an important role in the elution process. Under the optimal conditions, Fe3O4@SiO2-porphyrin showed good precision in intra-day (<8.9%) and inter-day (<13.0%) detection, low method detection limits (2-10u202fngu202fL-1), and wide linearity (10-10000u202fngu202fL-1). The method was applied to simultaneous analysis of 15 PAHs with acceptable recoveries, which were 71.1%-106.0% for ground water samples and 73.7%-107.1% for Yangtze River water samples, respectively.

Magnetic graphene solid-phase extraction in the determination of polycyclic aromatic hydrocarbons in water

In this work, magnetic graphene nanocomposite Fe3O4/rGO was fabricated by using a solvothermal method and applied to the magnetic solid-phase extraction (MSPE) of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples, followed by gas chromatography-mass spectrometry (GC-MS). Several parameters affecting the extraction efficiency, such as amount of magnetic graphene, extraction time, desorption conditions, were studied in detail. The results showed that Fe3O4/rGO has an extremely high adsorption capacity for PAHs, only 10 mg of the adsorbent was needed for 100 mL of water sample, and the PAHs could be completely desorbed with 100 μL of desorption solvent. Under the optimized conditions, a good linearity was obtained in the concentration range of 0.005–5 μg L−1 for 10 low ring PAHs from naphthalene to chrysene, 0.1–5 μg L−1 for benzo[b]fluoranthene, benzo[k]fluoranthene and benzo(a)pyrene. The limits of detection (LOD, S/N = 3) of the method were in the range between 0.02–14.3 ng L−1. The recoveries for PAHs tested in spiked water samples were in the range 75.6–112.4% with relative standard deviations (RSD) ranging from 0.1–9.5%. Finally, the method was successfully applied for the analysis of real water samples in the search for PAHs.

2α-Methylhopane: Indicator for Oil–Source Correlation in the Pearl River Mouth Basin, China

AbstractnOil samples collected from the Pearl River Mouth Basin (PRMB) were analyzed using comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxa0×xa0GC-TOFMS). High abundances of compounds in the 2α-methylhopane series were observed and accurately quantified. Although the 2α-methylhopane series can be a prominent biomarker in the oil and source rock samples, it has generally been used less than non-methylated hopanes. In this study, the 2α-MHI [C312α-methylhopanexa0×xa0100/(C312α-methylhopanexa0+xa0C30-αβ-hopane) (%)] ranges from 0.81 to 5.77% and 9.06 to 23.93% in Enping Formation- and Wenchang Formation-derived oils, respectively. The high abundance of the 2α-methylhopane series in Wenchang Formation-derived oils is attributed to anoxygenic phototrophs. The relevant 2α-methylhopane parameters showed correlations with C30-4-methyl steranes/∑C29 steranes, Pr/Ph and bicadinane-T/C30-αβ-hopane. Furthermore, the 2α-methylhopane series are rich in middle-deep lacustrine environments as well as marine sedimentary environment. The results indicated that the 2α-methylhopane series could be used as effective biomarkers to distinguish oils derived from different source rocks, as well as to enlarge the PRMB biomarker assemblages, which is beneficial to the evaluation of petroleum resources.

Magnetic extractant with an Fe3O4@SiO2 core and aqueous ammonia coating for microextraction of petroleum acids

Magnetic aqueous ammonia (MAA) was prepared as a magnetic extractant for dispersive microextraction of petroleum acids (PAs). The amount of extractant in MAA was custom-made by a simple approach. In the MAA composed of an aqueous ammonia coating and Fe3O4@SiO2 core, the coating is a base extractant that can selectively extract acids, while the magnetic core serves as a support to achieve dispersion as well as rapid magnetic retrieval of the extractant during the extraction processes. This is the first use of reusable, stable and modifiable Fe3O4@SiO2 as a support instead of bare Fe3O4 in a magnetic particle assisted dispersive liquid–liquid microextraction technique. The parameters that affect extraction efficiency were investigated. The sampling step as well as the desorption step can be completed in 2 min. The linear ranges are 5–5000 ng g−1, while the limits of quantification range from 2.5 to 6.2 ng g−1. The recoveries in spiked crude oil samples are in the range of 79.1% to 112.1% with relative standard deviations less than 11.3% (intra-day) and 13.4% (inter-day). Finally, the proposed method was applied to the analysis of PAs in diluted crude oils with different maturities. In comparison to the existing methods for extraction of PAs, the proposed method provides superior performances including high throughput (12-well plate), high degree of sample clean-up, and low consumption of separation material, solvent and time.

Hydrothermally tailor-made chitosan fiber for micro-solid phase extraction of petroleum acids in crude oils

Tailor-made chitosan fiber was prepared via hydrothermal treatment to serve as a micro-solid phase extraction (micro-SPE) sorbent for the analysis of petroleum acids (PAs) in crude oils. Chitosan fiber, which is commercial and cheap, has a diameter of about 10u202fμm and a length of a few centimeters. The fibrous property of the sorbent enables the micro-SPE to deal with viscous crude oil samples because of the low back-pressure during extraction, while the abundant hydroxyl groups and amino groups on the surface of chitosan fiber can provide high density of specific sites for adsorption of PAs. Moreover, it was found that hydrothermal treatment at certain conditions could tune the surface properties of chitosan fiber, leading to significant improvement of the capacity of the fiber in adsorption of PAs. Using hydrothermally treated chitosan fiber as sorbent, the micro-SPE was applied to the determination of PAs in crude oils, with the advantages of easy-operation, rapidness and high sensitivity (the limits of detection range from 0.7u202fng/g to 5.4u202fng/g). Furthermore, coupled with comprehensive two dimensional gas chromatography-mass spectrometry (GCu202f×u202fGCMS), the treated chitosan fiber packed micro-SPE method showed a great potential for comprehensive profiling of PAs in crude oils.