基質輔助鐳射解吸電離飛行時間質譜儀是一種重要的儀器被用來對生物樣品做結構分析，通過諸如源後裂解和碰撞誘導裂解兩種方式實現。然而同碰撞誘導裂解比較，源後裂解具有較低的裂解效率。 / 本課題的目的就是提升我們原有的基質輔助鐳射解吸電離飛行時間質譜儀在結構分析方面的能力。對儀器的改造包括(a)將原有的兩級反射器替換為曲線場反射器(b)安裝一個高壓浮地的碰撞室(c)安裝一個同軸的粒子探測器。曲線場反射器和同軸粒子探測器可以實現母離子跟碎片離子的同時監測，碰撞室可以實現母離子的碰撞裂解。在儀器的性能評估實驗中，母離子和所有的源後裂解的碎片離子同時被探測器記錄。在碰撞誘導裂解實驗中，母離子與碰撞氣體分子發生高能碰撞後大多生成了小質量數的碎片離子，實驗中還發現將碰撞室浮地後，碎片離子的質量解析度和信號強度都有了顯著改進。 / 通過比較曲線場反射器和兩級反射器的性能，我們提出了一種雜化反射器設計，這種反射器在第二片和最後一片電極片上都有可調電壓。第二片和最後一片電極片之間的電場遵循曲線場分佈。這種反射器有兩種操作模式：MS 和MS/MS 模式。類比實驗和分析計算的結果顯示在MS 模式裡，通過調整兩個可調電壓u1 和u2，不同質量離子在反射器裡的反轉點可以被設置在一個最優的位置從而得到最優的質量解析度。在MS/MS 模式裡，一個全質量範圍的譜圖和若干個較窄質量範圍的譜圖可以通過改變兩個可調電壓獲得，其中較窄質量範圍的譜圖具有更高的質量解析度用來分析某個質量範圍內的碎片離子的細節資訊。這些結果表明這種雜化反射器兼具曲線場反射器和兩級反射器的優點。 / Matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-TOFMS) is an important instrument for structural analysis of biological samples through such as post-source-decay (PSD) or collision-induced dissociation (CID) analysis. However, PSD analysis is a relatively low-efficiency method compared with CID analysis. / This project aims to upgrade the TOF instrument to a high performance TOF/TOF instrument. The modification involves (a) the replacement of the two-stage reflectron with a home-built curved-field reflectron (CFR); (b) the fabrication of a high voltage floated collision cell; and (c) the installation of a coaxial microchannel plate (MCP) detector. The CFR and coaxial detector allow simultaneous reflection of precursor ions and all fragment ions. The collision cell provides an effective means of ion activation (CID). In the performance test, precursor ions with almost all the fragment ions were recorded simultaneously in PSD analysis. In CID experiments, the precursor ions were found to undergo fragmentation due to high energy collision with the target gas and by floating the collision cell to high potential (several kV), the mass resolution and signal intensities of low mass fragment ions were improved substantially. / By comparing the performance of curved-field and two-stage reflectron, a hybrid reflectron was proposed, which has adjustable high voltages U1 and U2 on the second and last electrode element, respectively. The electrostatic potential between the second and last electrode element follows curved-field distribution. There are two operation modes for this reflectron: MS and MS/MS mode. Results from theoretical investigation and experiments showed that in MS mode, optimal energy compensation could be achieved through tuning the values of U1 and U2; in MS/MS mode, a full mass scale spectrum as well as spectra segments with high mass resolution within a narrower mass range could be obtained by setting U1 and U2 with appropriate values. These results indicated that the hybrid reflectron had the advantages both of curved-field reflectron and two-stage reflectron. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Li, Gang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 131-137). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese. / TABLE OF CONTENTS / LIST OF FIGURES / LIST OF TABLES / ABBREVIATIONS / Chapter Chapter One --- Background Introduction / Chapter 1.1 --- Matrix-assisted laser desorption/ionization (MALDI) --- p.2 / Chapter 1.1.1 --- Laser desorption --- p.2 / Chapter 1.1.2 --- Matrix-assisted laser desorption/Ionization --- p.3 / Chapter 1.2 --- Time-of-flight mass spectrometry --- p.8 / Chapter 1.2.1 --- Linear time-of-flight mass spectrometer --- p.8 / Chapter 1.2.2 --- Reflectron time-of-flight mass spectrometer --- p.9 / Chapter 1.2.2.1 --- Linear-field reflectron --- p.11 / Chapter 1.2.2.2 --- Nonlinear-field reflectron --- p.14 / Chapter 1.3 --- Structural analysis using time-of-flight mass spectrometer --- p.17 / Chapter 1.3.1 --- Post-source decay (PSD) analysis --- p.17 / Chapter 1.3.2 --- Collision-induced dissociation (CID) analysis --- p.20 / Chapter 1.4 --- Project introduction --- p.26 / Chapter Chapter Two --- Instrumentation / Chapter 2.1 --- Instrumentation --- p.28 / Chapter 2.1.1 --- Laser system --- p.28 / Chapter 2.1.2 --- Flight tube and vacuum system --- p.28 / Chapter 2.1.3 --- Ion source --- p.32 / Chapter 2.1.4 --- Deflector and time ion selector --- p.36 / Chapter 2.1.5 --- Two-stage gridless reflectron --- p.39 / Chapter 2.1.6 --- Detectors, digitizer and computer system --- p.42 / Chapter Chapter Three --- Fabrication of the Modified Tandem Time-of-flight Mass Spectrometer / Chapter 3.1 --- Introduction --- p.48 / Chapter 3.2 --- Implementation of a coaxial MCP detector --- p.51 / Chapter 3.3 --- Design, fabrication and implementation of a curved-field reflectron --- p.57 / Chapter 3.4 --- Design, fabrication and implementation of a floated collision cell --- p.61 / Chapter 3.5 --- Summary --- p.66 / Chapter Chapter Four --- Performance Evaluation of the Modified Instrument / Chapter 4.1 --- MS analysis by using the modified instrument --- p.68 / Chapter 4.2 --- MS/MS analysis by using the modified instrument --- p.73 / Chapter 4.2.1 --- Post-source-decay (PSD) analysis --- p.73 / Chapter 4.2.2 --- Collision-induced-dissociation analysis --- p.75 / Chapter 4.3 --- Mass calibration for the modified instrument --- p.84 / Chapter Chapter Five --- A Design of Hybrid Reflectron / Chapter 5.1 --- Introduction of the hybrid reflectron --- p.90 / Chapter 5.2 --- Characterization of the hybrid reflectron --- p.93 / Chapter 5.2.1 --- Calculations using analytical equations --- p.93 / Chapter 5.2.1.1 --- Analytical calculations for MS operation mode --- p.93 / Chapter 5.2.1.2 --- Analytical calculations for MS/MS operation mode --- p.99 / Chapter 5.2.2 --- Simulation experiments by SIMION --- p.106 / Chapter 5.3 --- Calibration of the instrument using the hybrid reflectron --- p.112 / Chapter 5.4 --- Summary --- p.115 / Chapter Chapter Six --- Fabrication and Performance Evaluation of the Hybrid Reflectron / Chapter 6.1 --- Hardware fabrication of the hybrid reflectron --- p.117 / Chapter 6.2 --- Performance evaluation of the hybrid reflectron --- p.121 / Chapter Chapter Seven --- Concluding Remarks --- p.128 / References --- p.131 / Appendix --- p.138 / Chapter Appendix 1 --- Mathematica program for analytical calculations / Chapter Appendix 2 --- Geometry file used in SIMION simulation experiment / Chapter Appendix 3 --- User program for controlling reflectron high voltage

Thesis (Ph. D.)--Oregon State University, 2001. / Typescript (photocopy). Includes bibliographical references (leaves 56-58). Also available online.

Thesis (Ph. D.)--University of New South Wales, 2002. / Also available online.

Thin-layer chromatography (TLC) is of great importance for the pharmaceutical industry as a simple, quick, and low cost analytical method. Considerable effort has been made over the past decades to combine the simplicity of TLC with the selectivity and sensitivity of mass spectrometry (MS) detection. In the pharmaceutical industry sensitivity is an especially important factor, since the allowed impurity level of most drugs is under 0.1%.The aim of the present thesis was to develop methods for the direct examination of pharmaceutical compounds from TLC plates by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI TOF MS). The study was started by comparing several approaches for the application of the matrix for direct TLC-MALDI including a newly developed electrospray matrix deposition method. This new method was found to be superior to the other techniques studied. It produced a stable signal, minimised analyte spreading, and hence allowed the scanning of a TLC plate to obtain chromatographic as well as mass spectral data. The plotted mass chromatograms assisted in spot location, and allowed the calculation of Rf-values. These showed good agreement with the Rf -values determined by UV detection. The decrease in mass resolution and mass accuracy commonly observed in TLC-MALDI TOF MS due to the uneven nature of the silica gel layer was corrected by internal recalibration on selected matrix ions during the scanning of the TLC plate. To enhance the signals recorded directly from a TLC plate the use of an extraction solvent prior the matrix application was explored. Further improvements in sensitivity were obtained by modifying a robotic x-y-z axis motion system to act as an electrospray deposition device and by use of special Si 60 F[254] HPTLC-MALDI targets. Using both approaches sensitivities in the high fmol range were obtained. To minimise matrix interference, which can suppress analyte signals, the application of suspensions of particles of different materials and sizes (Co-UFP, TiN, TiO[2], graphite and silicon) onto eluted TLC plates were investigated. The structural analysis of pharmaceutical compounds was achieved by post-source decay - matrix-assisted laser desorption/ionisation (PSD-MALDI) mass spectrometry performed directly on the separated spots. TLC-MALDI MS is not only applicable to the qualitative analysis of pharmaceutical compounds. The generation of quantitative data by using a structural analogue as an internal standard is also described. Different approaches to the incorporation of the internal standard into the TLC plate were tested. The most successful approach was to develop the TLC plate in the mobile phase to which the internal standard was added. Good accuracy, precision, linearity and sensitivity was obtained using this approach.

The performance of a linear matrix assisted laser desorption/ionization mass spectrometer (MALDI-oa-TOFMS) was improved with more reproducible sample preparation methods, a higher rate digitiser for integrating signals and customisable computer control, data acquisition and analysis in the LabVIEW?programming environment. This resulted in a ~20% improvement in resolution (up to 4,400) and enabled measurement of desorption velocities of 1,000 - 1,800 ms-1 for analytes with m/z 615 ?1,350 Da, with matrix ion velocities being 4,000 ?4,800 ms?. Detector limitations and restrictions on source axis energy (and hence velocity) required for the analysis of ions prevented detection of other species with this instrument. A 20 kV reflecting geometry MALDI-oa-TOFMS was constructed to overcome these limitations and extend the mass range. This mass spectrometer was able to analyse ions desorbed with a wide range of energies (32 ?197 eV). The resolution was found to be 8,000 -10,000. Best mass accuracy was 15-80 ppm (internal standards ). External calibration gave larger mass errors, mostly due to timing jitter, but the mass axis was stable for &lt2 weeks. Mass accuracy was independent of the analyte and matrix used. Ions with m/z of ~10,000 - 20,000 Da were observable with the use of a pulsed lens in the target region. This lens increased signal approximately 20 times, but degraded resolution. The detection limit of the instrument (sample consumed) was estimated to vary from 10 ?90 fmol, by extrapolation, with more moles required at higher m/z. The microsphere plate (MSP) electron multiplier used in the reflecting instrument was found to have a temporal response of &gt1 ns FWHM, but with a low secondary electron conversion efficiency, making it unsuitable for high m/z species. Experiments were also performed with a novel rectangular mesh grid, which (in correct orientation) provided similar resolution to conventional square mesh grids, but with significantly improved transmission and hence sensitivity.

In spite of their importance in many systems, liquid surfaces have been explored at the microscopic level to a much lesser extent than solids. Most surface analysis must take place in vacuum, a major drawback for liquids. The technique of time-of-flight scattering and recoil spectrometry (TOF-SARS) has been applied to molecular liquid surfaces for the first time. The apparatus borrows key elements from previous TOF-SARS experiments on solids and from molecular beam scattering (MBS) and features excellent surface specificity and the ability to detect all elements. A high-vacuum time-of-flight spectrometer was developed for the purpose of measuring the surface atomic concentration of atoms in low-vapor pressure liquid samples, and hence to infer preferred surface orientations. The TOF-SARS experiment involves surface bombardment with inert gas ions in the 1-3 keV energy range. During the interaction surface atoms may either (a) induce scattering of primary ions or (b) recoil from the surface. A binary collision model describes the kinematics and dynamics of the interactions well, allowing prediction of velocities and probabilities of particles leaving the surface. Particles that reach a detector along a ~1.1 m flight path are separated by velocity, and signals are collected as a histogram, revealing relative measured intensities that are converted to ratios of accessible surface atoms. Comparing the measured atomic ratios with computer-simulated accessible atomic ratios for various possible orientations gives insight into preferred surface orientation. A number of systems were explored m this work: liquids including a complementary pair of molecules having distinct 'head-tails' structures; glycerol as a highly H-bonded system, and a room-temperature molten salt. Preliminary results reveal that surface molecules appear in most cases to adopt some preferred orientation at the interface. The TOF-SARS technique was able to distinguish 'head' from 'tail' in molecules exhibiting that structure, suggesting only part of the head was accessible. In glycerol, all but two possible orientations were ruled out but the symmetrical nature of the molecule prohibits definitive assignment. The ionic liquid was found to have the cation and anion sharing the surface population roughly equally, and a preferred orientation for the substituted aromatic anion was discovered. / Graduation date: 2000

This thesis reports studies of methane dehydro-aromatization (MDA) over Zn-based/HZSM-5 catalysts and the catalytic conversion of acetylene gas (C2H2) on grain surface reactions using time-of-flight mass spectrometry (TOF-MS). Both catalytic reactions generate polycyclic aromatic hydrocarbons (PAHs) as their final products. For the MDA reaction, the performance of Zn-based/HZSM-5 catalysts prepared by wet impregnation method was investigated under the conditions of atmospheric pressure and supersonic jet expansion (SJE). The experimental results revealed that, under the SJE condition, the Zn/HZSM-5 catalysts exhibited high catalytic activity. It was also found that because of the rapid migration of H+ ions on the catalyst, the activation of CH4 at active sites of nano-ZnO is facile. A new reaction mechanism involving an active “ZnO-CH3+...-H-ZnO” intermediate formed as a result of synergetic action between ZnO and HZSM-5 has been proposed for the dissociation of methane and dehydrogenation. However, under atmospheric pressure, the catalytic activity of the Zn/HZSM-5 catalysts was low. The physical properties of the catalyst were characterized by Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), temperature-programmed reduction of H2 (H2-TPR), temperature -programmed desorption of NH3 (NH3-TPD), X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermogravimetric (TG/ DTG), and high-resolution transmission electron microscopy (HRTEM) techniques. For the catalytic conversion reaction of acetylene gas to form PAHs, the grains used were olivine and pyroxene-type silicates as well as alumina. Gas-phase PAHs were produced by the catalytic reaction of acetylene over crystalline silicates and alumina in a pulsed jet expansion condition and the gaseous products detected using time-of-flight mass-spectrometry (TOF-MS). In a separate experiment, further confirmation of the catalytic conversion of PAHs was obtained with the acetylene gas at atmospheric pressure flowing continuously through a fixed-bed reactor. The gas effluent and carbonaceous compounds deposited on the catalysts were dissolved separately in dichloromethane and analyzed using gas-chromatography-mass spectrometry (GC-MS). Amongst the samples studied, alumina showed higher activity than the olivine and pyroxene-type silicates grains. A mechanism for PAH formation is proposed in which the Mg2+ in silicates and Al3+ ions in Al2O3 act as Lewis acid sites for the acetylene reactions. Experimental investigation indicated that these silicates and Al2O3 particles are capable of providing catalytic centers for adsorption and activation of acetylene molecules that are present in the circumstellar environments of mass-losing carbon stars. The structure and physical properties of the particles were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and high-resolution transmission electron microscopy (HRTEM) techniques. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

No description available.

No description available.

Thesis (M.S.)--Rutgers University, 2007. / "Graduate Program in Biomedical Engineering." Includes bibliographical references (p. 23-24).