The Developments And Applications Of Some New Techniques Based On Photoionization Mass Spectrometry

A series of innovative progesses have been made in the fields of combustion and energy studies with the help of a "soft" ionization technique, i.e. synchrotron photoionization mass spectrometry (SVUV-PIMS) technique. However, poor performances (such as sensitivity, mass resolution etc.) of available mass spectrometers that can be applied for the SVUV-PIMS technique limit their applications, especially for complex research subjects, e.g. components analysis of petroleum and the pyrolysis mechanism of coal and biomass. Furthermore, very few types of mass spectrometers can be coupled to SVUV-PIMS technique. On the contrary, commercial mass spectrometers have many types with excellent performance after years of development. If the commercial mass spectrometers with mature techniques can be combined with the advanced SVUV-PI method, the advantages of both techniques will make it possible to study complex system more deeply and more widely than ever. However, it is hard to find a commercial mass spectrometer that can be installed directly into the synchrotron radiation facility due to its complexity. In this dissertation, we creatively combined the SVUV-PI technique with commercial mass spectrometers to develop two new apparatus for the anslysis of complex system, which can be named laser-induced acoustic desorption/synchrotron vacuum ultraviolet photoionization mass spectrometer (LIAD/SVUV-PIMS) and solid-pyrolysis/synchrotron vacuum ultraviolet photoionization mass spectrometer (Solid-Py/SVUV-PIMS), respectively. The processes of design, assembly and debugging of these two apparatus as well as their applications will be detailed in Chapters2and3. Morever, in order to better extend and popularize the PIMS technique in other common laboratories, the development of a discharge lamp based VUV-PIMS technique and some primary experimental results will be described in Chapter4.As described in Chapter2, LIAD/SVUV-PIMS apparatus mainly consisted of a home-made desorption/ionization chamber and a modified triple quadrupole time-of-flight mass spectrometer (QqTOF-MS). The aim of the modification is to introduce laser for samples desorption and SVUV light for ionization in QqTOF-MS. The process of the sample analysis is as follows:solid or liquid samples were firstly dissolved in appropriate solvent and the solution was deposited onto a Ti foil surface, which was introduced into the desorption/ionization-chamber by a linear driver after drying in air. Solid samples were desorpted by the infrared laser (1064nm) on the backside of Ti foil and the gaseous molecules were ionized by the SVUV light. Finally, the produced ions were analyzed by QqTOF-MS. The benefit of this technique is completely separating the laser and sample as well as the processes between desorption and ionization, so it can be qualified as "soft" desorption and "soft" ionization. In this dissertation, the LIAD/SVUV-PIMS apparatus performed well in the mass spectrometric analysis of fragile, thermal-unstable and petroleum samples.There are two types of Solid-Py/SVUV-PIMS apparatus, which can be worked at low and atmospheric pressure, respectively, which are decsribed in Chapter3. Both of them consisted of home-made pyrolysis and ionization chamber as well as QqTOF-MS. The low-pressure pyrolysis apparatus can avoid secondary reactions in the process of pyrolysis as much as possible, so it is benefit for studying pyrolysis mechanisms, while the atmospheric pyrolysis apparatus is closer to the actual pyrolysis condition. In a word, each types of apparatus has its own functions and applications. The atmospheric pyrolysis apparatus ultilized the skimmer with smaller diameter between pyrolysis and ionization chambers and added a turbo-molecular pump with the speed of100L/s compared to the low pressure one. During the experiments, gaseous species produced in the pyrolysis chamber passed through the first skimmer and entered the photoionizatin chamber and then intacted with SVUV light to generate ions, which were subsequently guided into QqTOF-MS to be analyzed. In this dissertation, the Solid-Py/SVUV-PIMS apparatus were applied for the pyrolytic study of various biomasses, such as cellulose, lignin, oak, and miscanthus. The final results indicate that Solid-Py/SVUV-PIMS are able to accomplish what other common apparatus could not achieve, for instance, controlling fragment ions, discriminating isomers, on-line detecting active speices (such as radicals) and so on.In Chapter4, we introduce a home-made radio frequency (RF) discharge lamp combining with commercial mass spectrometers as the ionization source in discharge lamp based VUV-PIMS apparatus. It is found that VUV photon flux produced by our RF discharge lamp is higher than1014photons/s regardless of which type of discharge gas was used. Therefore, we equipped the commercial QqTOF-MS and GC-MS with this VUV lamp for some testing experiments, primary results indicate that the performances of VUV lamp can meet the application requirements. However, some defects were found in the present RF VUV lamp, consequently a basic concept and plan for developing a discharge lamp based tunable VUV light source were proposed in the dissertation.Furthermore, there is a room to improve our developing apparatus and techniques, which were discussed objectively in the summary of each chapter including the future improvment methods. For the LIAD/SVUV-PIMS apparatus, the mass resolution of QqTOF-MS is still unsatisfying when we used it to characterize the components of hervy oils. Mass spectrometers with higher mass resolution are urgently needed for LIAD/SVUV-PIMS apparatus. For the Solid-Py/SVUV-PIMS apparatus, accurate quantitation and dynamic study of solid sample pyrolysis are hard to be achieved, the combination between Solid-Py/SVUV-PIMS and thermogravimity are needed in the future work. The application of discharge lamp based VUV-PIMS apparatus is limited in high divergence and broad band of VUV light. A monochromater with grating is needed for improving the performance of RF VUV lamp. In general, further improvements needs to be done in the future.