Carbon isotopic fractionation during vaporization of low molecular weight hydrocarbons(C6–C12)

Three series of laboratory vaporization experiments were conducted to investigate the carbon isotope fractionation of low molecular weight hydrocarbons（LMWHs）during their progressive vaporization.In addition to the analysis of a synthetic oil mixture,individual compounds were also studied either as pure single phases or mixed with soil.This allowed influences of mixing effects and diffusion though soil on the fractionation to be elucidated.The LMWHs volatilized in two broad behavior patterns that depended on their molecular weight and boiling point.Vaporization significantly enriched the ^13C present in the remaining components of the C6–C9 fraction,indicating that the vaporization is mainly kinetically controlled;the observed variations could be described with a Rayleigh fractionation model.In contrast,the heavier compounds（n-C10–n-C12）showed less mass loss and almost no significant isotopic fractionation during vaporization,indicating that the isotope characteristics remained sufficiently constant for these hydrocarbons to be used to identify the source of an oil sample,e.g.,the specific oil field or the origin of a spill.Furthermore,comparative studies suggested that matrix effects should be considered when the carbon isotope ratios of hydrocarbons are applied in the field.

Rapid chemome profiling of Artemisia capillaris Thunb. using direct infusion-mass spectrometry

Background:As one of the most popular traditional Chinese medicines(TCMs)for the treatment of various liver diseases,virgate wormwood herb(Artemisia capillaris Thunb.)has a long application history in TCM practices.It has been well established that the chemical composition is responsible for the pronounced therapeutic spectrum of A.capillaris.Although they are comprehensive,the time-intensive liquid chromatography coupled to tandem mass spectrometry(LCeMS/MS)assays cannot fully satisfy the analytical measurement workload from many test samples.Direct infusion-MS/MS(DIeMS/MS)may be the optimal choice to achieve high-throughput analysis if the mass spectrometer can universally record MS2 spectra.Methods:According to the application of gas phase ion fractionation concept,the MS/MSALL program enables to gain MS2 spectrum for each nominal m/z value with a data-independent acquisition algorithm via segmenting the entire MS1 ion cohort into sequential ion pieces with 1 Da width,when sufficient measurement time is allowed by DI approach.Here,rapid clarification of the chemical composition was attempted for A.capillaris using DIeMS/MSALL.A.capillaris extract was imported directly into the electrospray ionization interface to obtain the MS/MSALL measurement.After the MS1-MS2 dataset was well organized,we focused on structural characterization through retrieving information from the available databases and literature.Results:Twenty-six compounds were found,including 12 caffeoyl quinic acid derivatives,7 flavonoids,and 7 compounds belonging to other chemical families.Among them,24 ones were structurally identified.Compared with the LCeMS/MS technique,DIeMS/MSALL has the advantages of low-costing,solvent-saving,and time-saving.Conclusions:Chemical profiling of A.capillaris extract was accomplished within 5 min by DIeMS/MSALL,and this technique can be an alternative choice for chemical profile characterization of TCMs due to its extraordinary high-throughput advantage.

Carbon isotope fractionation during methane transport through tight sedimentary rocks:Phenomena,mechanisms,characterization,and implications

The phenomenon of carbon isotopic fractionation,induced by the transport of methane in tight sedimentary rocks through processes primarily involving diffusion and adsorption/desorption,is ubiquitous in nature and plays a significant role in numerous geological and geochemical systems.Consequently,understanding the mechanisms of transport-induced carbon isotopic fractionation both theoretically and experimentally is of considerable scientific importance.However,previous experimental studies have observed carbon isotope fractionation phenomena that are entirely distinct,and even exhibit opposing characteristics.At present,there is a lack of a convincing mechanistic explanation and valid numerical model for this discrepancy.Here,we performed gas transport experiments under different gas pressures(1–5 MPa)and confining pressures(10–20 MPa).The results show that methane carbon isotope fractionation during natural gas transport through shale is controlled by its pore structure and evolves regularly with increasing effective stress.Compared with the carbon isotopic composition of the source gas,the initial effluent methane is predominantly depleted in^(13)C,but occasionally exhibits^(13)C enrichment.The carbon isotopic composition of effluent methane converges to that of the source gas as mass transport reaches a steady state.The evolution patterns of the isotope fractionation curve,transitioning from the initial non-steady state to the final steady state,can be categorized into five distinct types.The combined effect of multi-level transport channels offers the most compelling mechanistic explanation for the observed evolution patterns and their interconversion.Numerical simulation studies demonstrate that existing models,including the Rayleigh model,the diffusion model,and the coupled diffusion-adsorption/desorption model,are unable to describe the observed complex isotope fractionation behavior.In contrast,the multi-scale multi-mechanism coupled model developed herein,incorporating diffusion and adsorption/desorption across multi-level transport channels,effectively reproduces all the observed fractionation patterns and supports the mechanistic rationale for the combined effect.Finally,the potential carbon isotopic fractionation resulting from natural gas transport in/through porous media and its geological implications are discussed in several hypothetical scenarios combining numerical simulations.These findings highlight the limitations of carbon isotopic parameters for determining the origin and maturity of natural gas,and underscore their potential in identifying greenhouse gas leaks and tracing sources.

Quantitative assessment of gas washing of oils in the Tazhong area of the Tarim Basin,Northwest China

Gas washing has been known in the Tazhong area of the Tarim Basin,but its quantitative assessment has not yet been reported.Here the influence of gas washing fractionation in the area was discussed based on the gas chromatogram data of 68 oils and the results of the mixing experiments of a black oil and a condensate.The results show that the intensity of gas washing fractionation decreased generally from northern to southern part and vertically from deep reservoirs to shallow reservoirs.The gas washing fractionation was mainly controlled by fault systems in this area,with the increase of n-alkane mass depletion positively correlated to the number and scale of faults.Gas washing fractionation appears to have affected the hydrocarbon property,and as a result the diversity of the crude oils is markedly controlled by gas washing.In addition,the occurrence of waxy oil in this area may be resulted from multiple factors including gas washing,mixed filling and migration fractionation.