| The application of lasers in solid sample analysis could date back to 1962,its subsequent combination with mass spectrometry(MS)technology became a milestone in the history of mass spectrometry for solid sample analysis.Compared with the traditional analysis methods,laser has unique advantages,such as simple pretreatment,low sample consumption,fast analysis,and less pollution.Therefore,it has been widely used in geological archeology,food safety,life science and medicine,plant environment analysis and many other fields.In addition,the combination of laser technology and mass spectrometry has the advantages of high sensitivity,good accuracy,superior identification capability,and wide dynamic range.Based on laser solid direct analysis,this dissertation describes the studies of the effect of elemental depth fractionation produced by laser ionization,and the application of mass spectrometry technology in plant palynology.The main research contents are given as follows:The first part:Although the combination of laser technology and mass spectrometry has many advantages,there exist one unavoidable defect,namely the fractionation effect.Laser ionization time-of-flight mass spectrometer(LI-TOFMS)in which laser directly acts on the ionization of sample without the aid of other auxiliary ionization sources.Therefore,the elemental fractionation effect induced by the depth of laser ablated crater can be directly studied.The instrumentations and methods used in the current study of laser sputter ionization elemental fractionation are summarized in detail,and the background and profound of this study are introduced.The effect of nanosecond laser and femtosecond laser ionization on elemental fractionation is compared.The results show that compared with the femtosecond laser ionization,nanosecond laser ionization results in a more wider region of thermal effects on the sample,making the surface component of the sample redistribute and thus deviate from the original value.But at a certain depth of the crater,the components are close to the true value.The occurrence of this process is closely related to the physicochemical properties of the elements in the sample,and the femtosecond laser ionization can significantly reduce the effect of element depth fractionation.The second part:Our home-made laser ionization time-of-flight mass spectrometry,which its unique ion source chamber,can realize the analysis of the elements and organics of the outer wall of the Chinese selaginella megaspore by controlling the pressure of the inert gas filled in the ion source chamber.The spore wall of Chinese selaginella megasporoe is composed of the outer wall and the inner wall.The spore center is protoplasm,and the outer wall of the spore contains anti-corrosive sporopollenin.The trace elements of the whole Chinese Selaginella megaspore are detectd by inductively coupled plasma mass spectrometry(ICP-MS),including Mg,Cr,Mn,Ni,Cu,Zn,Sn,Pb.LI-TOFMS is used to analyze the outer wall of this megaspore.The results show that it contains H,C,O,Mg,Si,Cl,K,and Ca.Si is not the essential element of life,but its content is very high in the outer wall of the spores.In addition,in the process of digestion,sporopollenin is very difficult to be digested.Without adding HF,the original megaspore of Selaginella sinensis would be digested to a white hollow sphere,which is exine sporopollenin.According to the spectral analysis of this white hollow sphere,the content of Si is still very high.It is believed that the outer wall of Chinese Selaginella megaspore has a strong ability to enrich Si,and that Si may have a place in the chemical structure of sporopollenin.In the LI-TOFMS organic spectrum,there may be an organic peak of p-coumaric acid,which is an important organic monomer that makes up sporopollenin.In addition,matrix-assisted laser desorption mass spectrometry(MALDI-TOFMS)is applied to directly analyze the outer wall,inner wall and protoplasm of Chinese Selaginella megaspore,keeping the natural state of each part. |
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