Development Of New Technique For Isotope Analysis Of Trace Hydrocarbon In Natural Gas Samples And Its Applications In Geochemistry

In the field of analytical chemistry,sample preparation technique is a important link in geochemical analytical.Due to the complexity of the geological sample matrix,sample preparation is particularly important in the process of geological analysis.The study of high-precision and high-sensitivity experimental analysis techniques for trace samples is one of the frontiers and main development directions in the field of geological research.In the study of oil and gas geochemistry,trace hydrocarbons provide considerable geochemical information,however,due to the limitation of analytical techniques,stable isotope analysis has not made any substantial progress.On the basis of solid-phase microextraction,this project initially proposed a new sample pretreatment technique Syringe-Solid Phase Extraction(SSPE).By optimizing the experimental conditions,the technique is applied to the study of oil and gas geological samples and achieved following progress:1.The sampler solid phase extraction technique uses a stationary phase adsorbent to selectively adsorb volatile target compounds in the mobile phase,and then desorbs by heating to achieve the effect of enriching trace or volatile hydrocarbon compounds.It can combine the extraction,enrichment,desorption and sample introduction as a whole.2.After optimizing the sampler solid phase extraction technique by different adsorbent types,adsorption equilibrium time and temperatures,desorption equilibrium time and temperatures and other experimental conditions,the best choice concerning condition is 13 X serve as a reliable adsorbent.Besides,adsorption at room temperature for 3~5 minutes,and desorption at 250~350? for 3~5 minutes.3.Carbon isotope analysis of source rock samples and different types of natural gas samples in the Sichuan Basin shows that the accuracy and accuracy of the data obtained are acceptable,and the error of the carbon isotope value of all hydrocarbon compounds is less than 0.48‰ without the appearance of obvious isotope fractionation.Undoubtedly,this result meets the requirements of GC-IRMS(Gas ChromatographyIsotope Ratio Mass Spectrometry).Compared with Solid-phase micro extraction-Gas Chromatography-Isotope Ratio Mass Spectrometry previous methods,more hydrocarbons were detected at lower levels of content.4.Using syringe-solid phase extraction technology to enrich trace ethane in natural gas and perform hydrogen isotope analysis test on the enriched ethane.The results show that the extraction results of trace alkane compounds by the sampler solid-phase extraction technology have reached the minimum detection limit of the instrument,and meet the requirements of hydrogen isotope value detection of trace hydrocarbons.