| Mass spectrometry is an analytical technique based on the mass-to-charge ratio of the ionized chemical species from the principles of physics.It has become one indispensible technique in modern analytical laboratory due to its high sensitivity,high specificity and high throughput.At present,the developents of new mass spectromtric techniques aiming at in situ,real-time,online,non-destructive analysis with low-consumption has become the important trend of mass spectrometry.The direct analysis of complex matrix has been one important challange for a long time in analytical chemistry.Since desorption electrospray ionization(DESI)and direct analysis in real time(DART)were introduced in 2004 and 2005 respectively,the direct analysi of complex matrix without sample pretreatment was made possible.Afterwards,the research of new ionization methods boomed all over the world and tens of new ion sources were reported based on different ionization mechanism such as photoionization,chemical ionization,electropray ionization and plasma ionization.Compared with other ionization methods,photoionization has the advantages of no polarity discrimination,soft ionization with low fragments and reduced ion suppression.The new mass spectrometries derived from photoionization have been widely applied in the surface analysis of complex sample such as insects,tablets,leaves and circuit board.However,it is still one challange for the quantitative analysis of compounds in complex matrix.In this dissertation,two new techniques based on vacuum ultraviolet(VUV)dischage lamp were invented for the qualitative and quantitative analysis of compounds in complex matrix directly.As decribed in Chapter 2,ultrasonic nebulization extraction was coupled with low pressure photoionization(UNE/LPPI)mass spectrometry.Ultrasonic nebulization extraction was composed of ultrasonic nebulizer,ultrasonic nebulization cell,heated transfter tube,condenser tube and gas system.Low pressure photoionization mass spectrometer was modified from a single quadrople mass spectrometer(Micromass LCZ).Firstly,the original electrospray ionization source was removed,then VUV dischage lamp was mounted on the forevacuum chamber which was pumped by one additional mechanic pump(8 L/s)and roots pump(40 L/s).After the analytes were ionized in the low pressure photoionization chamer,the ionized analytes were transferred by two skimmers and detected by a quadrople mass spectrometer.The whole process can be divided into two steps:the extraction of analytes from complex matrix in the unltrasonic nebulization cell and the ionization in the low pressure photoionization chamber.This technique made the direct analysis of complex matrices(like tea,sage leaf and Citrus aurantium peel)possible.In Chapter 3,the effects of solvent and ion source pressure for the analysis of anabolic steroids by low pressure photoionization(LPPI)mass spectrometry were studied.The reaction mechanisms of photo-induced ion-molecule reactions in low pressure and atmospheric pressure condition were similar,but the ion-molecule reactions in low pressure were simpler and easier to be elucidated.Results indicted that due to the higher proton affinity of acetonitril than methanol,acetonitrile adduct was stronger than methanol adduct in the positive LPPI mass spectrum;the analyte dissolved in methanol/water was easilier oxidized than in acetonitrile/water,because the photo-absorption cross-section of methanol for VUV light emitted from krypton dischage lamp was much lower than that of acetonitrile and more abundant superoxide ions O2·-formed for subsequent oxidation reactions.As the ion source pressure was elevated from 68 Pa to 800 Pa,the yields of solvent adduct and oxygen adduct increased with the increasing ion-molecule collision frequency.For the analysis of real complex sample,the experimental conditions can be chosen according to the requirements.In Chapter 4,extractive atmospheric pressure photoionization(EAPPI)mass spectrometry was combined with ultrasonic nebulization extraction and atmospheric pressure photoionization mass spectrometry,which is a new ambient ionization method.Compared with other photoionization related ambient mass spectromtries,EAPPI has three advantages:1)direct analysis of compounds in the internal parts of complex matrix;2)the direct quantitative analysis of chemicals in complex matrix with high sensitivity and good linear relationship;3)online monitoring of organic reactions.Resuts indicated that EAPPI can directly detect the chemicals not only in solid plant tissues,but also in compound amino acid in particle phase and heavy oil in viscous phase.The polycyclic aromatic hydrocarbons(PAHs)in soil can be quantified by EAPPI in a few seconds.When the ultrasonic nebulization cell was used as a reactor,EAPPI can be used to monitor oximation reaction in real time and study reaction dynamics.In Chapter 5,EAPPI mass spectrometry was used for the fast and comprehensive characterization of chemical ingredients in traditional Chinese herbal medicines.Traditional Chinese herbal medicines have been used in oriental countries for thousands of years and also the primary source of natural products.However,illegal activities such as shoddy products were inevitable in the huge international market of herbal medicines.In this part,EAPPI can characterize the ingredients including alkaloids,terpenes,polyphenols,lignans,flavonoids,amino acids,oligosaccharides and ginsenosides in herbal medicines comprehensively.The EAPPI results of two kinds of tripterygium glycosides tablet(TGT)from two manufacturers indicated the content difference of triptolide and tripterine,which can be used to interpretate the toxicological test results of these two tablets for the liver and kidney of mouse.Certainly,there are some shortcomings for the study in this dissertation.Firstly,all the work was conducted based on a VUV discharge lamp which has small size,but the photon flux was much lower than that of laser and synchrotron radiation,and the light wavelength was untunable.Thus the sensitivity can be increased by using a laser or synchrotron radiation source.Secondly,all experiments were completed on a single quadrople mass spectrometer or a single time-of-flight mass spectromter,thus the identifications of chemicals in complex matrices miss the structrue information from MS/MS spectra by tandam mass spectromter.Thirdly,in this dissertation,analytes should be gasified before they were ionized in the ionization region,thus it will be difficult for the analysis of heat-labile and non-volatile compounds,such as peptides and proteins.Maybe it will work if the sample was derivatived or using other desorption methods. |
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