| Mass spectrometry(MS)is a technical method for the chemical analysis based on the mass-to-charge ratio(m/z)of charged ions,with advantages of high sensitivity,high specificity,high accuracy,high throughput,low sample consumption,and fast analysis speed,which has become an irreplaceable analysis tool.Mass spectrometry has been developed very rapidly and widely used.It plays an important role in the fields of environment,life sciences,food,medicine,energy,and astronomy.Because the premise of mass spectrometry analysis is to make the sample molecules into charged ions,the development and application of ion sources are always an important research direction of mass spectrometry.Analytes can be ionized by absorbing energy from different sources such as photons,electric fields,and so on.At present,most analytes come from complex matrix samples.The rapid,accurate,and highly sensitive analysis of complex matrix samples has become a common concern in modern analytical chemistry.Traditional mass spectrometry ion sources,such as electron ionization(EI),chemical ionization(CI),electrospray ionization(ESI),and so on,have been commercialized and widely used in gas chromatography-mass spectrometry(GC-MS)and liquid chromatography-mass spectrometry(LC-MS),and have done a lot of research on the analysis of complex matrix samples.Although these methods have achieved good analysis performance,complex matrix samples need to be pretreated through extraction,purification,concentration,and so on.For some less-volatile and weak-polarity analytes,they need to be chemically derivatized before testing to improve ionization efficiency and detection sensitivity.It is also necessary to remove the interference from the matrix through separation and enrichment by chromatography column,to reduce the matrix effect on the ionization process.The whole analysis process is complicated,time-consuming,and solvent wasting,which can not meet the needs of modern analytical chemistry for in-situ,real-time,fast,high-throughput,low-loss detection of complex matrix samples.Compared with the traditional ionization methods,photoionization(PI)has the advantages of soft ionization,less affected by matrix effect,and no polar discrimination.PI is especially suitable for non-polar analytes,which are difficult to be directly ionized by ESI.Until now,PI has been widely used in the analysis of complex matrix samples in many fields,such as drugs,food,environment,biological science,and so on.However,the commercialized photoionization mass spectrometry still needs to be combined with chromatography to obtain high sensitivity and accuracy,which still has the disadvantages of long analysis time.This method can not fully meet the needs of real-time,fast,and high-throughput detection in modern analytical chemistry,as well.Because of the deficiencies in the above methods,thermal desorption was combined with photoionization mass spectrometry to achieve fast,accurate,high-throughput,high-sensitivity analysis of complex matrix samples without chromatographic separation.The first chapter introduces the development process and basic principles of mass spectrometry,including the common sample introduction system,the advantages,and disadvantages of the ion source,different types of mass analyzers and detectors.It also introduces traditional mass spectrometry methods and some new mass spectrometry techniques for complex matrix sample analysis.The second chapter introduces the establishment of thermal desorption atmospheric pressure photoionization mass spectrometry(TD-APPI-MS),the qualitative and quantitative analysis of steroids in standard solutions and natural water matrices,and discussion on the matrix effects in natural waters of river water,surface water,and tap water.The thermal desorption is induced by the Leidenfrost phenomenon to initiate a mild thermal analysis process.Analytes can be enriched while desorbing,which effectively improves the detection sensitivity.This method does not need to undergo sample pretreatment and chromatographic separation.One testing can be completed within 30 s.This method can achieve the direct,fast,accurate,high-throughput and high-sensitivity analysis of some analytes,which are difficult to volatile.TD-APPI-MS is especially suitable for the analysis of less-polar or non-polar compounds that are difficult to be directly ionized by ESI.The third chapter introduces the adjustment and improvement of TD-APPI-MS.Meanwhile,this method was applied for rapid,accurate,and highly sensitive quantitative analysis of trace free sex steroids in human serum.First,a heated connector was added,which connected with the TD holder,the VUV lamp,and the mass spectrometer inlet,making the device relatively integrated,as well as reducing sample loss.The size and temperature of TD holder were also adjusted.Besides,an RF-lamp with better performance replaced the previous DC-lamp.To gaining higher sensitivity and stronger stability,the improved TD-APP1 setup was combined with an LTQ-Orbitrap mass spectrometer,which has a higher mass resolution.Compared with chemiluminescence immunoassay(CLIA),which is commonly used in clinical sex steroids analysis,the improved TD-APPI-MS can more accurately quantify free sex steroids with higher biological activity in human serum.TD-APPI-MS can effectively avoid cross-reactions and false-positive results.Meanwhile,the quantitative results of the improved TD-APPI-MS were consistent with that of LC-MS.Finally,the improved TD-APPI-MS was applied to monitor the concentration of endogenous free sex steroids in women,who were at four different physiological stages of non-pregnancy,first trimester,second trimester,and third trimester.The relationship between the concentration of free sex steroids in woman’s serum and the specific physiological stages was studied.Finally,the quantitative results of endogenous free sex steroids in woman’s serum by the improved TD-APPI-MS and LC-MS showed high correlation consistency.The fourth chapter introduces the application of extractive atmospheric pressure photoionization mass spectrometry(EAPPI-MS)to rapid and accurate analysis of tobacco chemical components.EAPPI-MS combined sample extraction、desorption and ionization.Analytes can be quickly vaporized through a heated transfer tube.Compared with traditional LC-MS,EAPPI-MS did not need sample pretreatments and chromatographic separation,which has simple operation and fast analysis speed.One testing can be completed within 1 min.Because of the advantage of no polarity discrimination in EAPPI-MS,richer mass spectrum signals can be seen compared with LC-ESI-MS.46 kinds of chemical compounds including alcohols,ketones,acids,aldehydes,phenols,alkaloids,amino acids,and terpene were successfully identified using EAPPI-MS.The main chemical components and relative content in tobacco were comprehensively assessed.As well as,the relationship between the relative content of components and the quality of tobacco was studied.Different types of tobacco products were quickly distinguished using principal component analysis(PCA).EAPPI-MS has shown enormous potential in the rapid quality screening of abundant tobacco samples.The fifth chapter introduces in-situ,real-time,and online monitoring of the jasmine roasting process using homemade low-pressure vacuum ultraviolet photoionization time-of-flight mass spectrometry(VUV-PI-TOF-MS).A heated tube furnace was used to simulate the industrial roasting process.Jasmine can release chemicals during the roasting progress.At first,a fast and accurate qualitative analysis was carried out.Then,temperature programming and time accumulation methods were respectively used to study the changes of some main aroma components at different temperatures and times during the roasting process,which can help technicians to select the most suitable roasting temperature and time according to the processing purpose.VUV-PI-TOF-MS has shown great value in industrial applications.Finally,this thesis summarizes the main content of my work,presents the innovation and highlights,objectively discusses the possible improvements in my work,and puts forward some ideas for future study. |
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