This thesis describes a study of the technique and development of a system known as ASIA (Atomiser, Source, Inductively Coupled Plasmas (ICPs) in Atomic fluorescence spectrometry). Copper, nickel and lead boosted-discharge hollow-cathode lamps (BDHCLs), have been compared with the ICP, as excitation sources. A detailed study of the spectra of nickel and lead was performed. No evidence was found for the differences in the radiances between the two sources when the copper lamp was overrun. Although the lamps gave rise to lower blank standard deviation values, the detection limits were worse with the lamp source compared to ICP source. The modified Optica CF4 monochromator originally used, has been replaced by a Bentham Instruments computer controlled monochromator with better light gathering power. The optical arrangement for gathering the fluorescent radiation has also been re-designed. The performance of the modified system has been studied, based on detection limits (DLs), for a number of elements. In general, an improvement of 2 to 3 times in DLs is achieved. Further, improvements in the detection limits for molybdenum and tungsten have been achieved with the development of an on-line preconcentration procedure using a miniature column of Amberlite (IRA-93) anion-exchange resin. A heated spray chamber desolvation system has been evaluated as a sample introduction device for atomiser and source plasmas but, unfortunately the results obtained with the device were unsatisfactory. Problems included periodic instability of the plasmas and salt deposition on the inner walls of the spray chamber when high concentration solutions were aspirated. Also, a brief study of the feasibility of an aerosol modulation device has been performed. Finally, an interference study has been made to investigate the interference effects of high concentrations of interferent elements on a number of analyte elements. Spectral scans were obtained to visualise any possible interference effect. No spectral interference effect was observed on any of the analyte elements due to the interferent elements studied.

This work investigates the applicability of fast detectors to the technique of microscope-mode imaging mass spectrometry. By ionising analyte from a large area of the sample, and projecting the desorbed ions by the use of ion optics through a time-of-flight mass spectrometer onto a two- dimensional detector, time- (and hence mass-) dependent distributions of ions may be imaged. To date, this method of imaging mass spectrometry has been limited by the ability to image only one mass window of interest per experimental cycle, limiting throughput and processing speed. Thus, the alternative microprobe-mode imaging mass spectrometry is currently the dominant method of analysis, with its superior mass resolution. The application of fast detectors to microscope-mode imaging lifts the restriction of the detection of a single mass window per experimental cycle, potentially decreasing acquisition time by a factor of the number of mass peaks of interest. Additional advantages include the reduction of sample damage by laser ablation, and the potential identification of coincident eo-fragments of different masses originating from the same parent molecule. Theoretical calculations and simulations have been performed confirming the suitability of conventional time-of-flight velocity-mapped ion imaging apparatus for imaging mass spectrometry. Only small modifications to the repeller plate and laser beam path, together with the adjustment of the accelerating potential field, were required to convert the apparatus to a wide (7 mm diameter) field-of-view ion microscope. Factors affecting the mass and spatial resolution were investigated with these theoretical calculations, with theoretical calculations predicting a spatial resolution of about 26μm and m/m of 93. Typical experimental data collected from velocity-mapped ion imaging experiments were collected, and characterised in order to provide specifications for a novel time-stamping detector, the Pixel Imaging Mass Spectrometry detector. From these data, the suitability of thresholding and centroiding on the new detector was determined. Initial experiments using desorptionjionisation on silicon and conventional charge-coupled device cameras confirmed the correct spatial-mapping of the apparatus. Matrix-assisted laser desorptionjionisation techniques (MALDI) were used in experiments to determine the spatial and mass resolutions attainable with the apparatus. Experimental spatial resolutions of 14.4 μm and m/m of 60 were found. The better experimental spatial resolution indicates a higher di- rectionality of initial velocities from MALDI desorption than used in the theoretical predictions, while the poorer mass resolution could be attributed to limitations imposed by the use of the phosphor screen. Proof-of-concept experiments using fast-framing cameras and the new time-stamping detectors confirmed the feasibility of multiple mass acquisition in time-of-flight microscope mode ion imaging. Mass-dependent distributions were acquired of different pigment distributions in each experimental cycle. Finally, spatial-mapped images of coronal mouse brain sections were acquired using both conventional and fast detectors. The apparatus was demonstrated to provide accurate spatial distributions with a wide field-of-view, and multiple mass distributions were acquired with each experimental cycle using the new time-stamping detector.

Call number: LD2668 .T4 1958 C35 / Master of Science

Yeung, Hoi Sze. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 120-134). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

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

1 / Brittany K Casey

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A computer program to simulate peak shapes from time-of-flight (TOF) mass spectrometers has been developed and significantly improved from a previous, unpublished version. This program can accurately simulate both TOF and orthogonal acceleration TOF mass analyser peak shapes, with contributions from initial ion properties, instrument geometry, and other factors including high voltage ripple and detector response. Grid effects have also been included, and simulations for two mass spectrometers are compared to actual recorded spectra. The dispersive effect on ion trajectories of parallel wires and grids has been computationally studied and a model derived for each case. The model is based on the effect wire geometry has on the intrinsic focussing effect of the grid. The models for parallel wires and rectangular grids have been coded into the simulation program described above, and the effect of grids on peak shapes in TOF mass spectrometers has been studied. Good correlation between simulated and actual peak shapes for rectangular grids was obtained for grids in different rotational orientations. A pulsed lens has been developed to reduce the velocity spread of ions in matrix assisted laser desorption/ionisation (MALDI) ion sources, with the aim to increase sensitivity in orthogonal acceleration TOF mass analysers. The system gave an increase in sensitivity of approximately five times over a range of masses, however instrument resolving power was reduced. A rotating sample stage was developed for MALDI mass spectrometers which offers the potential of high sample density, high positional accuracy and repeatability, and low seek times. The system involves reading the position of a disk mounted with MALDI sample spots and timing the laser pulse to coincide with spot availability at an aperture. The system was successfully used to perform mass calibration by using a calibrant sample located on a separate spot to the analyte. Mass resolved disk imaging was also performed over a disk radius using inks. The mass resolved image compared well to the optical image.