A Study On Gasoline Recognition Based On Mass Spectroscopy And Chemometrics

As one of the major fuels of transportation,gasoline is widely used in vehicles,motorcycles,speedboats,helicopters and other transportation vehicles.Due to belonging to complex mixture,the variation in composition has a pronounced effect on the performance of gasoline.The composition of gasoline is closely related to its quality,which would affect the combustion efficiency of gasoline,engines,or pollutant emissions.Thus,it is significant to develop effective methods to evaluate gasoline quality.There are many kinds strategy to identify gasoline quality include Gas Chromatography,Spectroscopy,And Nuclear Magnetic Resonance.Although these methods play an important role in evaluating gasoline quality,there were still some disadvantages,such as expensive fund,tedious steps,or consuming time.For the quality control of gasoline in the fuel market,it is necessary to develop analytical methodologies with the features of sensitivity,precision,cost effectiveness,ease of use,and speediness.Mass spectrometry(MS)has been demonstrated to be a powerful technique for chemical analysis owing to its high sensitivity,high selectivity,and high specificity.In recent years,Due to its simplicity and high efficiency,chemometric methods in conjunction with MS has also been used to monitor gasoline adulteration or the compositions of petroleum crude oils.In order to further improve the performance of mass spectrometry in gasoline analysis,this thesis systematically explores the analysis performance of paper spray ionization mass spectrometry and direct analysis in real time ionization mass spectrometry for gasoline analysis,PSI and DART would been applied to discrimination of gasoline samples with different brands or gasoline adulteration.The detailed content including the following:(1)Establish paper spray ionization and direct analysis in real time ionization source methods.The paper spray ionization source applies the characteristics of the electrospray ion source to the paper substrate,so that the analyte is ionized at the tip of the paper substrate to generate a spray,and the atmospheric pressure ionization source technology integrates sample collection,separation,and ionization.In addition,the type of paper substrate,the angle of the triangular tip,and the type of spray solvent have an important influence on its analytical performance.The direct analysis in real time ionization is the ionization mass spectrometry ion source technology.The factors that affect the direct analysis in real time ionization source include the type and flow rate of the carrier gas,the moving speed of the guide rail,the heating temperature of the active material,and the grid electrode voltage.(2)The analytical gasoline performance of the paper spray ionization mass spectrometry was systematically researched.For the purpose of increasing the ionization efficiency of gasoline samples,various solvents(e.g.,methanol,ethanol,acetonitrile and isopropanol)were mixed with gasoline prior to PSI-MS analysis.The results demonstrated that a high polarity of applied solvent would lead to more information of gasoline samples in generated mass spectra,and 70%(v/v)of gasoline in gasoline/methanol admixtures gave the optimal condition.At the same time,it is also found that the spray voltage and paper matrix type have little influence on gasoline analysis during the PSI-MS analysis.Furthermore,through the analysis of 7 kinds of standard gasoline(89.0#,90.4#,91.0#,92.4#,93.9#,95.2#,99.4#)and 92# and 95# gasoline from different gas stations around Xi’an,it was found that the spectrogram and the established t-SNE model can quickly distinguish 92# and 95# gasoline of different standard gasoline from different gas stations,It was found that there was much difference in the gasoline samples from different companies,and even for those from the same refining company but from different gas stations.Further studies of the fingerprinting of gasoline samples indicated that the components of gasoline samples from different gas stations but from one refining company varied significantly,suggesting that no comparable standards were implemented in the refining process of gasolines.Also,PSI-MS was applied to discriminate gasoline adulterated with diesel,and as low as 1% of diesel in gasoline could be detected(3)Combining direct analysis in real time mass spectrometry(DART-MS)and principle component analysis research classification of commercial gasoline.Different experimental parameters,including the ratio between gasoline and methanol,heating temperature of helium,sample moving speed and helium gas pressure,were found playing vital roles to determine the analysis sensitivity of DART-MS.By evaluating the performance with three characteristic peaks from gasolines,abundant fingerprinting spectra of gasolines were achieved for later favorable brand classification.Furthermore,sampling mode was found crucial to the distinguishing ability of different brands of gasolines for the first time.Two frequently used sampling modes(sample card sampling and glass rod sampling)were compared to discriminate 6 brands of standard gasolines and 28 brands of the Research Octane Number(RON)92 and 95(namely 92# and 95#)commercial gasolines.In contrast to glass rod sampling,a full separation of different brands of gasolines was more favorable to be generated by using sample card sampling.In summary,the paper spray ionization mass spectrometry and direct analysis in real time mass spectrometry have been combined with the t-SNE and PCA models to evaluate gasoline quality.It could not only be directly applied to the classification of gasoline,but also can determine the content of diesel in gasoline.Adulteration is a quantitative result.At the same time,the impact of two different sampling modes of direct analysis in real time mass spectrometry was proposed for the first time about gasoline analysis.It laid the experimental foundation for the later real-time online gasoline analysis,and provided alternative and sensitive methodology for rapid evaluation of gasoline quality.