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1
Costello, Kevin Francis. "Laser desorption time-of-flight mass spectrometry." Thesis, University of Edinburgh, 1991. http://hdl.handle.net/1842/13475.
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The techniques of supersonic molecular beam cooling and laser multiphoton ionisation (MPI) spectroscopy have been combined to give a potentially powerful analytical technique. Two methods of sample introduction into the molecular beam have been employed, namely resistive heating and laser desorption. The resistive heating method allowed 2-colour MPI spectra of naphthalene, anthracene and perylene to be recorded in a simple free jet apparatus. A sensitivity for anthracene of 600 ppb is estimated. A time-of-flight (TOF) mass spectrometer has been developed, incorporating both linear and reflecting-geometry (reflectron) flight tubes, to allow laser desorption MPI (LD-MPI) mass spectra to be recorded for a number of involatile and thermally unstable compounds. Mass resolutions of 300 (linear) and 850 (reflectron) have been obtained for aniline. The constraints affecting the mass resolving power of both spectrometer designs are discussed. Finally, the potential of LD-MPI mass spectrometry as a sensitive, selective analytical technique is evaluated. The mass spectra of a number of polynuclear aromatic hydrocarbons, porphyrins and amino acids are presented, along with those of a simple mixture of the three aromatic amino acids tryptophan, tyrosine and phenylalanine. A sub-nanomole detection limit is estimated for tryptophan. Means to improve the sensitivity of the technique are discussed. The wider analytical applications of LD-MPI mass spectometry are considered.
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Hsi, Kuang-Ying. "Peptide identification of tandem mass spectrometry from quadrupole time-of-flight mass spectrometers." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p1462246.
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Thesis (M.S.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed May 4, 2009). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 45-46).
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Armitage, Nolan Jennifer Claire. "Time of flight mass spectrometry of pharmaceutical systems." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/13701/.
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Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a widely used surface chemical analysis technique that is traditionally employed to characterise the first few molecular layers of a material interface. The ability of this technique to accurately reflect the surface chemistry of polymers, biomaterials and many other solid materials is well documented. However, the majority of research that utilises this technique is based upon a qualitative rather than quantitative assessment of the material under investigation. The qualitative analysis of a range of traditional tablet and bead formulations containing drug and multiple excipients was performed in order to identify key diagnostic ions for all the different components. The lateral distributions of the ions across the surfaces of these formulations were imaged. Two different methods were then used to perform a qualitative analysis of the surfaces and results from these experiments were compared to the bulk composition. The effect of surface roughness on the ability to produce reproducible quantitative analyses from ToF SIMS ion yield data was investigated. A range of samples with different topographies were studied including polytetrafluoroethylene (PTFE), glass microscope slides, gold coated abrasive papers and gold coated precision measurement samples. The surface roughness was assessed by Atomic Force Microscopy and Laser Profilometry. Samples were analysed in imaging mode and the variance in ionization across the total image was measured for each sample. Evidence is presented that there is a relationship between ion yield and surface roughness, and that the surface roughness of the analysed surfaces will effect on any quantification approach in the processing of ToF-SIMS data. In addition, the presence of any orientation/directionality in surface features also needs to be evaluated when considering use of a quantitative approach. To investigate the effect of chemical environment on the ability to derive quantitative data from ToF SIMS analysis of pharmaceutical materials, drug loaded spun cast polymer films with low surface roughness were studied. ToF SIMS data were obtained for two chemically similar drugs in two different polymer matrices. In the majority of the samples there was no quantitative relationship between drug ion intensity and nominal bulk composition. Due to the large sample set, the multivariate technique, Principal Component Analysis (PCA) was employed to look at variance in secondary ion yields from the different samples. PCA is becoming more prevalent in ToF-SIMS data interrogation as it allows for a mathematically un-biased analysis of sample variables through the identification of the ions that account for the majority of the variance in the sample set. PCA successfully highlighted the impact of the chemical environment, showing secondary ion yields of drugs can be dependent on the surrounding matrix. PCA was also used to look at variance in two of the tablet samples and was successfully able to differentiate between the tablet samples with the lowest and highest concentrations of paracetamol. This thesis has demonstrated that surface topography and surface chemical environment or matrix will have a significant impact on ion yields in the ToF-SIMS experiments. These findings suggest caution in the use of ToF-SIMS for the quantitative analysis of complex chemically heterogeneous and topographically diverse pharmaceutical formulations.
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Ding, Luyi. "Studies of electrospray/ion mobility spectrometry/time-of-flight mass spectrometry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0015/NQ48344.pdf.
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Koeniger, Stormy Lee Ann. "Multidimensional ion mobility spectrometry coupled to time-of-flight mass spectrometry." [Bloomington, Ind.] : Indiana University, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3230539.
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Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2006.Title from PDF t.p. (viewed Nov. 5, 2008). Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4395. Adviser: David E. Clemmer.
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Clipston, Nigel L. "Laser desorption/laser ionization Time-of-Flight Mass Spectrometry." Thesis, University of Salford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360476.
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Dale, Michael John. "Laser desorption laser photoionisation time-of-flight mass spectrometry." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/13547.
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The work described in this thesis is concerned with the development and application of laser desorption laser photoionisation time-of-flight mass spectrometry (L2TOFMS). This technique has been used to enable photoionisation mass spectra of a very wide variety of involatile and thermally labile molecules to be recorded. The instrument used for this work is described along with an overview of the fundamental principles behind this methodology. A number of specific classes of molecules have been studied using the L2TOFMS. These include polyaromatic hydrocarbons, porphyrins, dyestuffs and a variety of analytically important staining agents. The advantages of this approach for analysing complex mixtures, which yield relatively simple mass spectra, have been demonstrated for both environmental systems and commercially important mixtures. It has also been shown that L2TOFMS can be used for the direct interrogation of target systems adsorbed onto organic substrates. L2TOFMS has been used to probe the photophysics of both porphyrin molecules and a series of azo dyes. Ionising wavelength dependent fragmentation was observed for a number of metallotetraphenylprophyrins and metallo- octaethylporphyrins. Using 193 nm laser photoionisation, molecular dissociation, involving loss of the macrocycle side groups, was shown to be similar to that obtained by electron impact ionisation. Whereas, at 266 nm, fragmentation via a neutral intermediate state, resulting in the loss of the metal from the macrocycle, competes with further photon absorption. Characteristic azo-bond photoreductive cleavage has been observed for azo molecules when using 266 nm laser photoionisation. This behaviour is linked to the cis-trans photoiosomerisation of the azo bond.
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Torbet, Tyler S. "Analysis of Synthetic Cannabinoids by Direct Analysis in Real Time Quadrupole Time-of-Flight Mass Spectrometry and Gas Chromatography Quadrupole Time-of-Flight Mass Spectrometry." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2216.
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The aim of this study was to investigate the utility of direct analysis in real time quadrupole time-of-flight mass spectrometry and gas chromatography quadrupole time-of-flight mass spectrometry in the analysis of 162 different synthetic cannabinoids. Direct analysis in real time quadrupole time-of-flight mass spectrometry is shown to be a rapid and accurate analytical method for synthetic cannabinoids. Spectra can be generated with less than 1.5 ng of the drug in under a minute and be successfully searched against previously generated ESI-QTOF libraries in most cases (118/130 drugs tested) as well as can also be applied to the identification of synthetic cannabinoids in a mixture. Gas chromatography quadrupole time-of-flight mass spectrometry, while requiring a much longer analysis time, is shown to accurately distinguish all but 19 compounds (140/159). These two instruments have proven to be viable alternatives in synthetic cannabinoid analysis and will greatly benefit forensic laboratories.
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Quiniou, Michel L. M. "Development and application of tandem time-of-flight mass spectrometry." Thesis, University of Edinburgh, 2001. http://hdl.handle.net/1842/12820.
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A novel tandem time-of-flight (TOF) mass spectrometer has been developed for studying the photo-induced dissociation of large molecules and elemental clusters. It consists of a linear first stage TOF analyser for primary mass separation and precursor ion selection, and a second orthogonal reflecting field TOF analyser for product ion analysis. The instrument is equipped with a large volume throughput molecular beam source chamber allowing the production of jet-cooled molecules and molecular clusters, as well as elemental clusters, using either a pulsed laser vaporisation source (LVS) or a pulsed arc cluster ion source (PACIS). A second differentially pumped chamber can be used with effusive sources, or for infrared laser desorption of large molecules, followed by laser ionisation. These primary ions can then be irradiated with a second, high energy laser to induce photodissociation. Detailed information about the fragmentation mechanisms can be deduced from the product ion mass spectra. A theoretical overview of the technique of tandem time-of-flight mass spectrometry is presented, together with a detailed description of the experimental procedures and equipment used. In order to assist with the design and optimisation of the instrument a "virtual" mass spectrometer was drawn to scale using the SIMION software program, in order to simulate ion trajectories for differing voltage, geometry's and dimensions of the ion optics. An ion gate was designed and manufactured to provide primary mass selection following the first time-of-flight mass analyser. The device consisted of four layers of interleaved wires; primary ions could be selectively transmitted by application of a fast rising high voltage pulse to the middle set of wires. The mass gate was measured to have a mass resolving power, m/Dm = 30.
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Ipsen, Andreas. "Probabilistic modelling of liquid chromatography time-of-flight mass spectrometry." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/6903.
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Liquid Chromatography Time-of-Flight Mass Spectrometry (LC-TOFMS) is an analytical platform that is widely used in the study of biological mixtures in the rapidly growing fields of proteomics and metabolomics. The development of statistical methods for the analysis of the very large data-sets that are typically produced in LC-TOFMS experiments is a very active area of research. However, the theoretical basis on which these methods are built is currently rather thin and as a result, inferences regarding the samples analysed are generally drawn in a somewhat qualitative fashion. This thesis concerns the development of a statistical formalism that can be used to describe and analyse the data produced in an LC-TOFMS experiment. This is done through the derivation of a number of probability distributions, each corresponding to a different level of approximation of the distribution of the empirically obtained data. Using such probabilistic models, statistically rigorous methods are developed and validated which are designed to address some of the central problems encountered in the practical analysis of LC-TOFMS data, most notably those related to the identification of unknown metabolites. Unlike most existing bioinformatics techniques, this work aims for rigour rather than generality. Consequently the methods developed are closely tailored to a particular type of TOF mass spectrometer, although they do carry over to other TOF instruments, albeit with important restrictions. And while the algorithms presented may constitute useful analytical tools for the mass spectrometers to which they can be applied, the broader implications of the general methodological approach that is taken are also of central importance. In particular, it is arguable that the main value of this work lies in its role as a proof-of-concept that detailed probabilistic modelling of TOFMS data is possible and can be used in practice to address important data analytical problems in a statistically rigorous manner.
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Thomas, Benjamin. "Tandem time-of-flight mass spectrometry incorporating quadratic-field technology." Thesis, University of Warwick, 2000. http://wrap.warwick.ac.uk/66998/.
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The study involved the desig~ constructio~ optimisation and utilisation of a novel tandem time-of-flight (TOF-TOF) instrument. The instrument was designed to use a laser ion source capable of laser desorption or matrix-assisted laser desorption/ionisation. The instrument used a twin ion mirror geometry in which the first ion mirror was a single-stage ion mirror, while the second ion mirror was a quadratic-field ion mirror. The instrument was designed for highenergy (>10keV) collision-induced dissociation (CID). The initial design criteria of a tandem time-of-flight spectrometer are discussed. The design and construction of the vacuum chamber and pumping system are discussed. The design and construction of the laser ion source are covered in detail. Computer simulations of typical ion trajectories were calculated using the SIMION program. The design and construction of the steering optics, single-stage ion mirror and pulsed mass gate are discussed. Computer simulations of ion trajectories were used to characterise the ion optical properties of the system. Experiments to characterise the energy focusing properties and transmission of the single-stage ion mirror were conducted. The mass resolving power of the single-stage ion mirror were characterised. The single-stage ion mirror achieved a resolution of2000 full-width half-maximum (FWHM). The design and construction of the differentially pumped collision-cell and the quadratic-field ion mirror are outlined. Experiments to demonstrate the transmission of the collision-cell and quadratic-field ion mirror are discussed. Experiments to characterise the energy focusing properties of the quadratic-field ion mirror were conducted. The full instrument achieved precursor mass resolving powers of approximately 7000 (FWHM) for laser desorbed species and 3500 (FWHM) for MALDI generated peptide species. Initial CID results are presented. The study thoroughly discusses the problems with the current instrument configuration and goes on to propose solutions to the problems encountered.
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Papanastasiou, Dimitris. "Space velocity correlation in orthogonal time-of-flight mass spectrometry." Thesis, Manchester Metropolitan University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423073.
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Selby, David Sean School of Chemical Sciences UNSW. "Matrix assisted laser desorption/ionization orthogonal acceleration time-of-flight mass spectrometry: development and characterization of a new instrument." Awarded by:University of New South Wales. School of Chemical Sciences, 2002. http://handle.unsw.edu.au/1959.4/18784.
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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 <2 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 >1 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.
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Watson, R. Craig Jr. "Laser-Ionization Time-of-Flight Mass Spectrometry of High Molecular Mass Inorganic Complexes." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35554.
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Laser-Ionization Time-of-Flight Mass Spectrometry (LI-TOF-MS) is a sophisticated tool for the molecular-weight determination and structural characterization of a variety of molecules. Advances in instrumentation and ionization methods have recently expanded its role in the analysis of high-mass analytes. Large multimetallic complexes, which are efficient solar-energy converters, rely heavily on their chemical structure for optimum operation. Molecular mass determinations of these multimetallic complexes have been problematic due to their lability and high molecular weights.
This thesis describes the characterization of a LI-TOF-MS instrument and confirmation of theoretical time-of-flight mass-separation principles. Several test cases demonstrate the instrument's proper operation and calibration for a wide mass range of analytes. Mass spectral results of three organometallic compounds: i. [Ir(dpp)2Cl2](PF6), ii. {[(bpy)2Ru(dpp)]2IrCl2}(PF6)5, and iii. {[(bpy)2Ru(dpp)]2RuCl2}(PF6)5 under a variety of laser ionization and sample preparation conditions are compared. A complete structural characterization of the monometallic complex, [Ir(dpp)2Cl2](PF6), is presented. The two trimetallic analytes fragmented easily, but significant components of the molecules are successfully identified. After optimizing the ionization and analytical procedure, LI-TOF-MS proved useful in the analysis of high molecular mass metal complexes.
Master of Science
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Williams, C. M. "Development of an orthogonal acceleration time-of-flight mass spectrometer : structural and quantitative applications in mass spectrometry." Thesis, Swansea University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636619.
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This thesis describes the development of a prototype orthogonal acceleration time-of-flight mass spectrometer, constructed at Swansea University (2002). This instrument incorporated design features to improve the duty-cycle of the time-of-flight mass spectrometer and was designed to conduct MS and MS/MS. Ion optical interfaces for full-beam transmission and collision-induced dissociation were developed. This work characterises the transport efficiency of the interfaces with a SCIEX electrosprayer. Ion transmission was dependent on the ion optical configuration, lens voltages, orifice sizes and stagnation pressure. Due to time limitations the full instrument was not completed and experimental work finalised on a commercial time-of-flight. A study of the ion structure of C4H4+ was carried out. A new method relying on consecutive reactions for controlling the internal energy of ions was used. Collision induced dissociation spectra of C4H4+ allowed the composition of the ion beam to be monitored and the vinylacetylene and methylenecylcopropene structures dominated. An observation was made for the fragmentation C4H4+ ® C3+., C3H1+, C3H2+ and C3H3+ for C4H4+. formed in the ion source, compared to C4H4+ formed in a field-free region. Their collision-induced dissociation mass-analysed ion kinetic energy (CID-MIKE) spectra were very different, which could not be accounted for in terms of structural and possibly internal energy differences. This is a highly reproducible effect requiring further study. Matrix-assisted laser desorption/ionisation (MALDI) was used on a ‘Voyager-DE STR’ to develop a survey technique analysis of nucleotides. The matrix α-cyano-4-hydroxyxinnamic acid matrix provided good sensitivity (<10pmol). MALDI as a quantitative tool was investigated. There are major challenges to overcome before MALDI can be reliably used for quantitation of nucleotides. An experimental survey of over 900 accurate mass measurements was made on 10 compounds and showed that accurate masses could be reliably obtained for 40% of adenosine monoshosphate samples but for quanosine di- and triphosphates this fell to near zero.
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McClenathan, Denise M. "Advances in plasma source mass spectrometry with a time-of-flight mass analyzer." [Bloomington, Ind.] : Indiana University, 2005. http://wwwlib.umi.com/dissertations/fullcit/3162280.
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Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2005.Title from PDF t.p. (viewed Dec. 2, 2008). Source: Dissertation Abstracts International, Volume: 66-01, Section: B, page: 0253. Chair: Gary M. Hieftje.
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Ekroos, Kim. "Characterization of Molecular Glycerophospholipids by Quadrupole Time-of-Flight Mass Spectrometry." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2003. http://nbn-resolving.de/urn:nbn:de:swb:14-1071755489156-08653.
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The physical properties of glycerophospholipids (GPLs) are not only determined by the head group (HG), but also by their fatty acid (FA) chains, which affect their distribution and function within membranes in the cell. Understanding the microheterogenity of lipid membranes on a molecular level requires qualitative and quantitative characterization of individual lipids and identification of their FA moieties. The aim of my study was to introduce the new technology of multiple precursor ion scanning (MPIS) on a QSTAR Pulsar time-of-flight mass spectrometer (QqTOF) to analyze lipids. Detailed information on fatty acid composition of individual GPL molecules could be obtained in parallel with conventional profiling of lipid classes, and this could be done by direct analysis of total lipid extracts. This method was termed Fatty Acid Scanning (FAS) and Head Group Scanning HGS, respectively. In this way the molecular GPL composition of total lipid extracts could be charted in a single analysis accurately and rapidly at a low picomole concentration level. Furthermore, combining FAS and HGS together with ion trap MS3 analysis allowed complete charting of the molecular composition of PCs, including quantification of their positional isomers, thus providing a detailed and comprehensive characterization of molecular composition of the pool of PCs. Development of the Lipid Profiler software allowed full automation and rapid processing of complex data, including identification and quantification of molecular GPLs. This approach was evaluated by preliminary applications. First, the molecular composition of PCs of total lipid extracts of MDCK cells and of human red blood cells (RBC) could accurately be charted. Significant presence of positional isomers was observed increasing the total number of individual PC species close to one hundred. Secondly, the molecular PC and SM species distribution in detergent resistant membranes (DRMs) prepared by Triton X-100 DRMs were analyzed and were found to be enriched in distinct GPLs. The distribution in PCs and SMs of Triton X-100 DRMs of RBC were compared with those of the DRMs of MDCK cells. Finally, combining the use of a 96 well plate and a robotic system demonstrated that these analyses can be automated and analyzed with high throughput. This system we termed Shotgun Lipidomics. Taken together, this mass spectrometric methodology provides rapid and detailed insight into the distribution of the molecular GPLs of membranes and membrane sub-fractions.
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Redpath, Craig Robertson. "Applications of laser desorption laser photoionisation time-of-flight mass spectrometry." Thesis, University of Edinburgh, 1995. http://hdl.handle.net/1842/12846.
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This thesis describes the development and application of laser desorption laser photoinisation time-of-flight mass spectrometry (L2TOFMS) for the analysis of polymers and related systems. L2TOFMS has been little used in this area until now. In the past, this technique has been used extensively for the study of high mass, involatile and/or thermally labile species such as biomolecules, porphyrins and dyestuffs. The theory behind the main experimental principles is discussed and the equipment used is described in detail. The main body of the thesis is concerned with the generation of high quality polymer mass spectra. Utilising several ionisation wavelengths, the mass spectra of several aromatic polymers have been obtained for the first time. For two model polystyrene systems, polystyrene 800 and 2500, a series of intense oligomer peaks and some fragments were observed at each photoionisation wavelength employed. Fragments were shown to occur in the laser desorption event, a phenomenon previously documented. However, an intact oligomer series for these polymers had never previously been observed using this technique. The data obtained allowed a complete and unambiguous characterisation of the polystyrenes to be made. Molecular weight averages were calculated from the spectra. When 193 nm photoinisation was employed, these values compared favourably to those supplied by the manufacturer. However, photoinisation by either 248 nm or 266 nm UV radiation resulted in mass spectra which gave lower molecular weight averages. This was primarily due to oligomer fragmentation at these wavelengths. The analysis and characterisation of a fluorinated polystyrene and phenyl containing siloxane polymer was also carried out. L2TOF mass spectra were also recorded for several polymer additives in their pure form. Two compound classes of additive were studied, namely UV stabilisers and phenolic antioxidants.
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Qu, Guangzhi. "Resolution Limits of Time-of-Flight Mass Spectrometry with Pulsed Source." W&M ScholarWorks, 2016. https://scholarworks.wm.edu/etd/1477068405.
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Matrix Assisted Laser Desorption/Ionization (MALDI) is a time-of-flight mass spectrometry commonly used to detect a wide mass range of biomarkers. However, MALDI requires a high laser pulse energy to create ions with a mass higher than 50,000 Daltons. That high laser energy increases the net ion production but it also degrades the instrument's mass resolution. This project uses a Room Temperature Ionization Liquid (RTIL) as a liquid matrix with a self healing surface instead of a standard crystal matrix to increase shot to shot reproducibility, enabling a systematic study of the origin of the resolution degradation. This study shows that the main source of the resolution degradation is the ionic space charge which delays the ejection of ions into the acceleration region, essentially increasing the ionization pulse time to be as long as hundreds of nanoseconds. This study includes simulation and experimental results to document this effect.
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Lewin, Mark James Chemistry Faculty of Science UNSW. "Instrument development and computational studies of time-of-flight mass spectrometers." Awarded by:University of New South Wales, 2006. http://handle.unsw.edu.au/1959.4/39745.
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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.
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Westmacott, Garrett R. "Ion desorption, detection & dissociation in time-of-flight mass spectrometry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://hdl.handle.net/1993/1716.
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The results of everal fundamental experiments on desorption/ionization and fragmentation in time-of-flight mass spectrometry are described. The yield of desorption of secondary. molecular ions of valine was determined as a function of primary ion mass with a tandem time-of-flight mass spectrometer. The primary ions consisted of alkali metals Li$\sp+$, Na$\sp+$, K$\sp+$, Rb$\sp+$ and Cs$\sp+$ with impact energy on the valine target ranging between 3.5 and 10keV. The yield measurements for both negative and positive molecular valine ions were found to correspond to the cube of nuclear stopping power, and low mass ions, like H$\sp-$ and C$\sp-$ were found to scale linearly with the nuclear stopping power. Secondary-ion and secondary-electron emission yields from surfaces bombarded with large molecular ions were measured in a tandem time-of-flight mass spectrometer. The primary ions were produced by matrix-assisted laser desorption/ionization and ranged in mass from 6000u to 110 000u, and in energy from 5 to 25keV. The yields were measured for surfaces of stainless steel and CsI. For a given energy, the secondary electron yield decreases rapidly for increasing mass but remains greater than $\sim$10%; in contrast, the efficiency of secondary ion production remains close to unity. For high velocities, the electron yield is significantly higher for the CsI surface, but for velocities corresponding to less than $\sim$0.4eV/u, the emission is rather insensitive to the surface. An alternative method for the analysis of metastable-ions in a reflecting time-of-flight instrument is demonstrated. Post-source decay analysis usually involves collecting fragment ion spectra in segments, decreasing the mirror voltage for each segment. The present method leaves the mirror voltage fixed and increases the accelerating voltage to acquire each segment. The central advantage is that the mass calibration depends sensitively on the mirror voltage but only weakly on the accelerating voltage. The method of post source decay analysis is also demonstrated with precursor ion selection using a Bradbury-Nielsen ion gate. Finally, the forth experiment involves measuring molecular ion yields as a function of laser fluence for matrix-assisted laser desorption/ionization. This experiment was done on two different instruments. One is a linear time-of-flight mass spectrometer where both analog and pulse-counting detection methods are used and compared. The second instrument is an orthogonal-injection time-of-flight instrument with collisional cooling and pulse-counting detection. It is an improvement relative to the linear instrument because it ensures single-ion counting. The results for both instruments and detection methods were consistent. The ion yield versus laser fluence was found to have a steep slope on a log-log plot (between 6 and 9) for a range of fluence covering almost an order of magnitude. Also no evidence was observed for an ion desorption threshold at low laser fluence ($\sim$10J/m$\sp2$).
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Bowerbank, Christopher Ryan. "Comprehensive Isotachophoresis-Capillary Electrophoresis Coupled to Time-of-Flight Mass Spectrometry." BYU ScholarsArchive, 2001. https://scholarsarchive.byu.edu/etd/6084.
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Isotachophoresis (ITP) coupled to capillary zone electrophoresis (CE) in a comprehensive manner was used to separate mixture components in both insufficient and sufficient concentrations without heart-cutting or splitting. Examples of comprehensive ITP-CE involving multiple CE injections of preconcentrated ITP zones are demonstrated. In the comprehensive arrangement, all of the sample in the first dimension (ITP) is subjected to analysis in the second dimension (CE), without significant sample loss or decrease in sample detectability resulting from removal of a portion of the sample. This is especially important for analytes at low concentrations which may form a single mixed zone instead of individual ITP zones. Direct online coupling of ITP to CE in this comprehensive arrangement involved the use of columns having different diameters with one directly inserted inside the other. A counterflow was applied when the isotachophoretic sample stack reached the bifurcation point. Large volume (10 µL) injections were made using an electrically-insulated commercial polymeric rotary valve injector for increased reproducibility compared to previous comprehensive ITP-CE studies, with ITP and CE retention time RSD values ranging from 2-5%. An ultraviolet (UV) detector positioned at the bifurcation point was used to determine the beginning of CE injection. Application of a splitting voltage at the bifurcation point showed no affect on analyte transfer into the CE column. By using multiple injections of the ITP band(s), CE column overloading was not observed.
Online capillary isotachophoresis (ITP) and comprehensive isotachophoresis-capillary electrophoresis (ITP-CE) were also coupled with electrospray ionization (ESI)-orthogonal acceleration time-of-flight mass spectrometry (TOFMS). Separations were performed using 200 µm I.D. and 50 µM I.D. polyvinylalcohol (PVA)-coated fused silica capillaries for ITP and CE, respectively. Both ITP and ITP-CE were coupled to TOFMS for analysis of sufficient (10-5 M) and insufficient (10-6-10-7 M) concentrations of angiotensins in mixtures. ITP-TOFMS of a single mixed zone of five angiotensins (3 x 10-7 M) showed that ion suppression due to the co-elution of angiotensin III in the electrospray significantly reduced the ionization of other analytes. A practical solution to the detection difficulties for ITP mixed zones involved the insertion of a CE separation between the ITP and TOFMS for online preconcentration, separation, and identification in one system.
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Hankin, Steven Mark. "Laser post-ionisation time-of-flight mass spectrometry of polycyclic aromatic hydrocarbons." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/1208.
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Crecelius, Anna Christina. "Thin layer chromatography-matrix assisted laser desorption ionisation-mass spectrometry of pharmaceutical compounds." Thesis, Sheffield Hallam University, 2002. http://shura.shu.ac.uk/19512/.
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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.
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Winter, Benjamin. "Novel methods in imaging mass spectrometry and ion time-of-flight detection." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:43db5039-0490-4f97-8519-4d3ed4e30ca3.
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Imaging mass spectrometry (IMS) in microscope mode allows the spatially resolved molecular constitution of a large sample section to be analysed in a single experiment. If performed in a linear mass spectrometer, the applicability of microscope IMS is limited by a number of factors: the low mass resolving power of the employed ion optics; the time resolution afforded by the scintillator screen based particle detector and the multi-hit capability, per pixel, of the employed imaging sensor. To overcome these limitations, this thesis concerns the construction of an advanced ion optic employing a pulsed extraction method to gain a higher ToF resolution, the development of a bright scintillator screen with short emission lifetime, and the application of the Pixel Imaging Mass Spectrometry (PImMS) sensor with multi-mass imaging and time stamping capabilities. Initial experimental results employing a three electrode ion optic to spatially map ions emitted from a sample surface are presented. By applying a static electric potential a time-of-flight resolution of t/2Δt=54 and a spatial resolution of 20 μm are determined across a field-of-view of 4 mm diameter. While the moderate time-of-flight resolution only allows particles separated by a few Dalton to be distinguished, the instrument is used to demonstrate the multi-mass imaging capabilities of the PImMS sensor when being applied to image grid structures or tissue samples. An improved time-of-flight resolution is achieved by post extraction differential acceleration of a selected range of ions (up to 100 Da) using a newly developed five electrode ion optic. This modification is shown to correct the initial velocity spread of the ions coming off the sample surface, which yields an enhanced time-of-flight resolution of t/2Δt=2000 . The spatial resolution of the instrument is found to be 20 μm across a field-of-view of 4 mm. Adjusting the extraction field strength applied to the ion optic of the constructed mass spectrometer allows the optimised mass range to be tuned to any mass of interest. Ion images are recorded for various samples with comparable spatial and ToF resolution. Hence, studies on tissue sections and multi sample arrays become accessible with the improved design and operational principle of the microscope mode IMS instrument. A fast and efficient conversion of impinging ions into detectable flashes of light, which can consequently be recorded by a fast imaging sensor, is essential to maintain the achievable time-of-flight and spatial resolution of the IMS instrument constructed. In order to find a suitable fast and bright scintillator to be applied in a microchannel based particle detector, various inorganic and organic substances are characterised in terms of their emission properties following electron excitation. Poly-para-phenylene laser dye screens are found to show an outstanding performance among all substances analysed. An emission life time of below 4 ns and a brightness exceeding that of a P47 screen (industry standard) by a factor 2× is determined. No signal degradation is observed over an extended period, and the spatial resolution is found to be comparable to commercial imaging detectors. Hence, these scintillator screens are fully compatible with any ion imaging application requiring a high time resolution. In a further series of mass spectrometric experiments, ions are accelerated onto a scintillator mounted in front of a multi pixel photon counter. The charged particle impact stimulated the emission of a few photons, which are collected by the fast photon counter. Poly-para-phenylene laser dyes again show an outstanding efficiency for the conversion of ions into photons, resulting in a signal enhancement of up to 5× in comparison to previous experiments, which employed an inorganic LYSO scintillator.
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Hunsucker, Stephen Warren. "Time-of-Flight Mass Spectrometry to Characterize Inorganic Coordination Complexes and Cyanobacteria." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/27150.
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Matrix assisted laser desorption/ionization time-of flight mass spectrometry (MALDI-TOFMS) is used to study several inorganic coordination complexes and a variety of compounds from cyanobacteria. Also presented is a discussion of TOFMS instrumentation and the improvements in resolution and instrument automation that have lead to widespread and diverse applications of MALDI-TOFMS in all areas of science.
The feasibility of using direct laser desorption/ionization (LDI) TOFMS to detect trace elements in a variety of glass samples using a lithium borate fusion technique for sample preparation is investigated. The result of the fusion technique is a homogeneous incorporation of the analytical sample into a glass. The fusion technique is investigated as a way to eliminate matrix effects in direct LDI-TOFMS analysis. However, the high concentration and low ionization potential of lithium suppress ionization of the elements of interest. The detection limits of elements in glass samples were not at the trace level. Therefore the technique is not as useful as well-established analytical methods like X-ray fluorescence and inductively coupled plasma mass spectrometry.
Direct laser ablation and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of four inorganic coordination complexes are discussed. The compounds studied include [Ir(dpp)2Cl2](PF6), {[(bpy)2Ru(dpp)]2RuCl2}(PF6)4, [(tpy)Ru(tpp)Ru(tpp)RhCl3](PF6)4 and {[(bpy)2Ru(dpp)]2IrCl2}(PF6)5 (dpp = 2,3-bis-(2'-pyridyl)-pyrazine, bpy = 2,2'-bipyridine, tpy = 2,2',6',2"-terpyradine, tpp = 2,3,5,6,-tetrakis-(2'-pyridyl)-pyrazine). Spectral intensities and fragmentation patterns are compared and evaluated for several instrument parameters, matrices, and matrix-to-analyte ratios. Direct ablation and MALDI mass spectra of the monometallic complex showed the same ion peaks and differed only in the relative peak intensities. Direct ablation of the trimetallic complexes produced only low-mass fragments containing one metal atom at most. MALDI spectra of the trimetallic complexes exhibited little fragmentation in the high-mass region (>1500 Da) and less fragmentation in the low-mass region compared to direct laser ablation. Proper matrix selection for MALDI analysis was vital, as was an appropriate matrix-to-analyte ratio. The results demonstrate the applicability of MALDI-TOF mass spectrometry for the structural characterization of labile inorganic coordination complexes. A correlation is made between the gas-phase redox chemistry in the MALDI plume and the solution phase electrochemistry for this series of complexes.
MALDI-TOFMS was also used to study compounds isolated from cyanobacteria. A MALDI screening method has been developed to detect the presence of scytonemin, a UV-absorbing pigment. Detection of scytonemin is accomplished by a simple solvent extraction of cyanobacteria in the desiccated state with subsequent MALDI-TOFMS analysis. The method is rapid and semi-quantitative. Cyanobacteria is the only known organism to produce scytonemin, and it is only produced when the organism is subjected to UV stress. Laboratory-grown cultures were subjected to different amounts of UV radiation, and the screening method was used to detect the presence or absence of scytonemin. Cultures grown under ambient conditions (low UV) did not show the presence of scytonemin, while those grown under UV lamps did show the detectable scytonemin. Because scytonemin acts as a biomarker for UV stress, the MALDI screening method could find application in molecular ecology studies of cyanobacteria.
Peptide mass fingerprinting is used to monitor the isolation of the water stress protein from N. commune. The protein is produced by recombinant growth in E. coli in order to assess the role of Wsp in the desiccation tolerance of N. commune. The results show that SDS-PAGE and Western blot analysis are not sufficient to detect the presence of Wsp after purification using ion-exchange chromatography. Three E. coli proteins were identified in the same molecular weight range as Wsp and one of them cross-reacts with the series of antibodies used for the Western blot. The presence of contaminating proteins that cross-react with the immuno assay make it difficult to determine which fractions contained Wsp. Peptide mass fingerprints were obtained for a series of fractions collected after ion-exchange chromatography to pinpoint the location of Wsp. Peptide mass fingerprinting was also used to monitor the stability of the clone and results show that the clone is modified over a six month period.Ph. D.
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Sinha, Amanda E. M. "Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry with chemometric analysis /." Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/8566.
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Lloyd, Paul M. "Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of synthetic polymers." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343833.
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Galhena, Asiri S. "Implementation of an In-line Surface-induced Dissociation Device in a Quadrupole Time-of-flight Instrument and Its Performance." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195832.
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The focus of this dissertation is the introduction of surface-induced dissociation (SID) into a commercially available quadrupole time-of-flight mass spectrometer as an alternative ion fragmentation method. The performance of the SID device was characterized and its applications were demonstrated by dissociating peptides, proteins, inorganic salt clusters and non-covalent protein complexes. The SID setup allowed direct comparison of SID with conventional collision-induced dissociation (CID) on the same instrument, taking advantage of the characteristics of Q-TOF instrumentation, including extended mass range, high sensitivity and resolution. With the SID setup installed, no significant reduction of the ion transmission was evident. SID fragmentation patterns of peptides are, in general, similar to CID, with slight differences in the relative intensities of immonium ions, backbone cleavage b- versus y- type ions, and y- versus y-NH3 ions. This suggests enhanced accessibility to high energy/secondary fragmentation channels with SID. SID studies on cesium iodide clusters (CsI) also revealed that SID deposits more internal energy.The utility of mass spectrometric methods to probe the gas phase cyclization process was studied with [D-Ala2]-Leucine Enkephalin amide. This peptide showed prominent formation of the [M-NH3]+ ion which is believed to be the linear b5 ion with a C-terminal oxazolone structure. Other fragments in the spectra indicate that the linear b5 ion undergoes cyclization, subsequent ring opening and further dissociation to rearranged fragments that cannot be explained by the initial sequence. The similarities between the cyclic and b5-ion from the linear peptide indicated the formation of a heterogeneous ion population and this is further supported by gas-phase H/D exchange experiments. An ion funnel interface to improve ion transmission at high pressures was tested in a custom built quadrupole-surface-quadrupole instrument. The ion transmission efficiency for selected bio-molecules such as YGGFLR, insulin chain-B, ubiquitin and cytochrome c showed to approach almost 90%, with the funnel interface installed. The ion transmission efficiency was effected by several factors including: the size of the analyte, the DC gradient, the RF frequency, and the RF amplitude. The higher fragmentation efficiencies for SID in the presence of the funnel interface indicated higher internal energy deposition for the funnel interface.
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Simpson, David C. "Combining capillary electrochromatography with ion trap accumulation and time-of-flight mass spectrometry." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/638.
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Capillary electrochromatography (CEC) is a rapidly developing liquid chromatographic technique in which electroosmotic flow (EOF) is used to propel mobile phase through the chromatographic column. The use of EOF results in reduced band dispersion when compared with pressurised flow, but narrow capillaries are required to avoid dispersion due to heating that arises from the required application of high electrical potentials. Measurement of UV absorbance in these narrow capillaries is therefore relatively insensitive, demanding improved detection methods. This work presents an alternative strategy that is based on the combination of ion trap accumulation with time-of-flight mass spectrometry. Electrospray is most often used to transfer analytes from solution to the gas phase, concomitant with ionisation, when interfacing CEC to mass spectrometry. The small volumetric flow rates encountered in CEC, however, raise the possibility of other types of interface being effective. The work presented here describes the development of a novel interface in which a pulsed IR laser is used to vaporise chromatographic eluent, followed by ionisation using a pulsed UV laser. Vaporisation and ionisation both occur within the ion trap to remove the possibility of transmission losses. Ionisation laser wavelength is varied to impart a degree of selectivity. The presence of vaporised solvent and analyte ions inside the trap offers the possibility of performing ion-molecule chemistry. In developing this instrument, the electrochromatographic column was separated from the interface by an electrically grounded junction and a transfer capillary. To preserve chromatographic efficiency, the fluid dynamics of this junction between the column and the transfer capillary were investigated both computationally and experimentally. Simulations of the fluid dynamics of the junction are presented. In order to test the interface without the intermittent, chromatographic, delivery of analyte, a continuous leak inlet was employed. The performance of the instrument was evaluated with polycyclic aromatic hydrocarbons because they are important environmental pollutants and because they are amenable to laser ionisation at 266 nm. Expressed as a number of theoretical plates per metre, an average chromatographic efficiency of 95,000 was obtained with a test mixture that consisted of acenaphthene, biphenyl, fluorene, naphthalene and phenanthrene. Furthermore, using the leak inlet, naphthalene was detected as a 100 nM solution in acetonitrile.
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Smith, Robert W. "An evaluation of miniaturised field asymmetric waveform ion mobility spectrometry hyphenated with time-of-flight mass spectrometry." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/17837.
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In this thesis, the performance of a miniaturised field asymmetric waveform ion mobility spectrometry (FAIMS) device hyphenated with time-of-flight mass spectrometry is studied and evaluated for analysis of a variety of compounds in different sample matrices. FAIMS is a selective spectrometer which is highly orthogonal to mass spectrometry and has the potential for enhancing sensitivity and improve selectivity of rapid analyses. In Chapter 2, the performance of the miniaturised FAIMS device is tested for stability and transmission under a wide range of ion source conditions. An investigation of three different systems, including pairs of isobaric, isomeric and near-mass ions shows that miniaturised FAIMS has the ability to distinguish between analytes that are challenging to separate by mass spectrometry. Chapter 3 explores the effect of changing the composition of the carrier gas by observing the effect of adding gas modifiers on the FAIMS spectra of small molecules, peptides and proteins. Chapter 4 investigates the advantages of combining a fast FAIMS separation with mass spectrometry in the analysis of nitrogen-containing pharmaceutical impurities, where FAIMS is found to offer additional selectivity. In Chapter 5, the development of a UHPLC-FAIMS-MS method for the quantitative determination of a drug metabolite in urine is reported. UHPLC-FAIMS-MS shows improvements in signal-to noise and linear dynamic range as well as a reduction in chemical noise, demonstrating the potential of combining FAIMS with mass spectrometry.
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Robins, Chad LaJuan. "Nonpolar matrices for matrix assisted laser desportion ionization - time of flight - mass spectrometry." Cincinnati, Ohio : University of Cincinnati, 2005. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1115293526.
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Thesis (Ph. D.)--University of Cincinnati, 2005.Title from electronic thesis title page (viewed May 18, 2006). Includes abstract. Keywords: Matrix Assisted Laser Desorption/Ionization Mass Spectrometry; MALDI; Nonpolar Matrices; Charge-Transfer Ionization; Crude Oil; Mass Spectrometry. Includes bibliographical references.
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Hamilton, Jacqueline Fiona. "Complex mixture analysis using time of flight mass spectrometry and comprehensive gas chromatography." Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405677.
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Ghumman, Chaudhry Amjad Ali. "Time-of-flight secondary ion mass spectrometry: new application for urinary stones analysis." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2013. http://hdl.handle.net/10362/8796.
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Karahan, Mehmet Cem. "Laser-assisted secondary ion mass spectroscopy and its applications in practical surface analysis." Thesis, Montana State University, 2004. http://etd.lib.montana.edu/etd/2004/karahan/KarahanM0805.pdf.
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Yang, Zhongyu. "Performance Advantages of Maximum Likelihood Methods in PRBS-Modulated Time-of-flight Energy Loss Spectroscopy." Fogler Library, University of Maine, 2003. http://www.library.umaine.edu/theses/pdf/YangZ2003.pdf.
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Schriemer, David Christopher. "Development and application of laser-based ionization techniques in time-of-flight mass spectrometry." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23066.pdf.
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Sodeman, David Alan. "Characterization of ambient, automobile, and diesel aerosols utilizing aerosol time of flight mass spectrometry /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3144344.
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Raptakis, Emmanuel N. "High resolution, high sensitivity tandem mass spectrometry of macromolecules using time-of-flight techniques." Thesis, University of Warwick, 1996. http://wrap.warwick.ac.uk/110843/.
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The first of the three parts of this study involves the construction of a large scale time-of-flight mass spectrometer. A large aluminium-alloy vacuum chamber was designed and manufactured. Ion trajectory modelling was carried out for defining the optimum ion optical configuration of the matrix-assisted laser desorption/ionisation (MALDI) ion source that was designed and constructed. A floating ion detector assembly was designed and installed. MALDI mass spectrometry experiments were performed with biomolecules and polymer samples. The second part of this work involves the design and construction of a MALDI ion source in the collision cell area of a four-sector tandem mass spectrometer. The apparatus makes use of an array detector installed as the detector of the second double-focusing mass analyser of this instrument. High resolution and sensitivity mass spectra of high mass biomolecules and polymer samples were acquired. Resolution in excess of 3500 full-width at half maximum (FWHM) has been observed. The third part of this work describes the theoretical considerations, the design the construction and the performance of a prototype magnetic sector/time-of- flight tandem mass spectrometer with an ideal time-focusing ion mirror as the second mass analyser (Mag-TOF). The method followed in order to overcome the inherent incompatibilities of the two mass-analysis stages is discussed. The theoretical description of the ideal time-focusing reflectron is presented, together with analysis of the time-aberrations of the delivery ion optics and the TOF part of the instrument, and their influence to resolution and sensitivity. Initial experiments have been performed to prove the feasibility of the operational principle of this prototype instrument. High resolution (approximately 3000, FWHM) tandem mass spectra of peptides are presented. The instrument also achieved high levels of sensitivity.
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Alvarez, David A. "The development of time-of-flight mass spectrometry techniques for studying the surface of Europa for astrobiology." Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2009m/alvarez.pdf.
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Marsden, Nicholas. "The development of an aerosol time-of-flight mass spectrometer for the measurement of mineral dust." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/the-development-of-an-aerosol-timeofflight-mass-spectrometer-for-the-measurement-of-mineral-dust(907c6eee-be07-466a-b1b6-46c6ce9ab8ca).html.
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The development of new analytical techniques is one of the driving forces in the advancement of scientific understanding. The measurement of the properties of aerosol particles is an active area of research due to the impact aerosol has on atmospheric processes. Single particle size and composition are key properties that govern many atmospheric processes, but the measurement of these properties is challenging due to the large dynamic range of size and composition that exists in the environment. Mineral dust represents a significant fraction of the global aerosol mass loading and has a profound impact on the earth's radiative budget through the direct interaction with solar and terrestrial radiation, and by affecting microphysical properties of clouds. In addition, mineral dust is involved in the geochemical cycling of many compounds that are vital for the health and vitality of ecosystems. The importance of the chemical and crystallographic properties of a material, or mineral phase, has been highlighted recently. Measurements of the elemental composition of single particles is possible with off-line analysis of dust collected on filters , but mineral phase is usually obtained from X-ray diffraction of bulk samples. These techniques are labour intensive and the lack of ambient measurements is a limiting factor in the development of models that attempt to resolve the complexity of atmospheric processes. Time-of-flight mass spectrometry (TOF-MS) is well suited to on-line single particle composition measurements due its sensitivity and high temporal resolution. Single particle mass spectrometry (SPMS) is a class of TOF-MS technique that is able to identify mineral dust particles from their chemical signature in the mass spectrum. Analysis of refractory mineral dust by mass spectrometry requires laser desorption ionisation (LDI) by high energy pulsed lasers, a process that renders the composition measurement non-quantitative due to incomplete ionisation and matrix effects. Consequently, the identification of mineral phase is not possible because the reproducibility of the measurement is lower than the natural variation between common minerals. This thesis reports the development of a commercially available single particle mass spectrometer for the measurement of the physiochemical properties of mineral dust. The optical particle detection system is improved for the more efficient detection of single particles in the size range relevant to the ambient measurement of mineral dust aerosol, and a model is developed that will aid the further development of particle detection in SPMS. A novel method for the on-line differentiation of mineral phase in single particles is presented which exploits differences in ion arrival times at the TOF-MS detector of a silicate molecular ion species, that arise from the influence of mineral phase on the ion formation process during the LDI process. The efficacy of the technique is demonstrated with the differentiation of mineral phase in laboratory generated mineral dust from clay mineral standards. The deployment of the improved instrument to measure Saharan dust outflow resulted in the first ever on-line identification of the clay mineral fraction in ambient mineral dust.
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Piehowski, Paul D. Ewing Andrew Graham. "Investigating lipid heterogeneity in single cells using time-of-flight secondary ion mass spectrometry." [University Park, Pa.] : Pennsylvania State University, 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-4585/index.html.
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Toner, Stephen Mark. "Anthropogenic particulate source characterization and source apportionment using aerosol time-of-flight mass spectrometry." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3283574.
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Thesis (Ph. D.)--University of California, San Diego, 2007.Title from first page of PDF file (viewed November 21, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Fong, C. W. Van (Chun Wan Van) 1973. "Phase space dynamics in a linear RFQ trap for time-of-flight mass spectrometry." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36924.
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A new Linear RFQ Ion Trap/Axial Time-of-Flight mass spectrometer was developed and tested. A segmented quadrupole rod system was used to create a static axially confining field that could trap and cool an ion cloud from a DC ion source. In addition, an adjustable extraction field was applied, after sufficient ion collection, by pulsing the trapping rod segments to send the cooled ion cloud into a collinear Time-of-Flight spectrometer. Two chevron stacked multichannel plates, with a measured charge amplification of 3.75 x 107, were used as a detector at the end of the flight tube.The purpose of this work was to investigate ion dynamics in the linear trap (LTRAP) so as to determine the suitability of this system as a source for TOFMS. The trap was therefore designed to be relatively weak so that the ion collection volume would be large enough to obtain a detailed picture of the cloud. The system was tested using a Cs+ (m/ z =133) ion source. Optimal parameters were found to be an applied well depth of -5V to -15V with a q value between 0.3 and 0.6 in a buffer gas environment of N2 at pressures of 10 -4 Torr or greater. Under these conditions and a cooling/collection time of 50ms the trap was observed to contain about 2500 ions. This translated to a detection efficiency of about 26.7% of the ions entering LTRAP.
Computer simulations based on a thermodynamic model were created to analyze the experimental data. The ion ensemble was found to reach an equilibrium temperature of 0.0353 +/- 0.0025eV in less than 10ms. Another computer program was used to reconstruct the phase space density of the LTRAP collection from the detector signals. The results of this reconstruction agreed with the results obtained from the model fitting procedure thereby confirming the thermodynamic model.
The phase space density distribution in LTRAP showed that with a time-focusing reflectron even this weak trap would have a m/Delta m = 250. This has led to guidelines for the construction of a high-resolution hybrid mass spectrometer using a linear ion trap. Based on these current results, a mass resolution of almost 10,000 is predicted as an upper limit of this type of mass spectrometer.
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Mowat, Ian A. "Synthetic polymer analysis using matrix assisted laser desorption/ionization time-of-flight mass spectrometry." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/12128.
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The aim of the work described in this thesis was to assess 'Matrix Assisted Laser Desorption/Ionization' (MALDI) Time-of-Flight mass spectrometry as a possible technique for the analysis of synthetic polymers. A compact home-built time-of-flight mass spectrometer of cylindrically symmetrical geometry was used to carry out all the mass spectrometry detailed described in this thesis. A survey of the literature describing the development of matrix assisted laser desorption/ionization spectrometry and also the previous analysis of polymers by laser mass spectrometry was carried out. Experiments comparing the performance of the apparatus with published data on peptides and proteins were carried out, followed by experiments to assess the possibility of analyzing synthetic polymers. Initially polar polymers were investigated, since they could be anlayzed using sample preparations very similar to those developed for peptide and protein analysis. Later investigations were carried out on non-polar polymers such as polystyrene. The attachment of a range of transition metals to a low mass polystyrene was investigated using laser desorption/ionization time-of-flight mass spectrometry, without the use of matrices to increase the ion yield. Systematic investigations into the effects of sample spot composition, i.e. the amounts of matrix, polymer and salt present, were carried out, and used to suggest possible models for the processes leading to the generations of large gas phase ions. The effects of sample spot composition on the size and shape of the polymer molecular weight distributions obtained was also investigated. Liquid polymers such as polysiloxanes and perfluorinated polyethers were investigated using laser desorption/ionization and matrix assisted laser desorption/ionization. Carbon cluster generation from such polymers was investigated, and fullerene and polycyclic aromatic hydrocarbon analysis was also briefly studied. Novel new molecules such as aryl ester dendrimers were investigated, since they could not be successfully analyzed by other mass spectrometric techniques. Single molecular ions were obtained, helping to confirm the expected masses of these molecules. Novel new polymers such as hyperbranched aromatic polyesters were also analyzed, and molecular weight distributions were successfully obtained for a number of samples, showing the utility of MALDI for the analysis of new materials.
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Li, Yun [Verfasser]. "Atmospheric Trace Gas Measurements Using Chemical Ionisation Time-of-Flight Mass Spectrometry / Yun Li." Wuppertal : Universitätsbibliothek Wuppertal, 2021. http://d-nb.info/1234170744/34.
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Samiveloo, Silverraji Chemistry Faculty of Science UNSW. "High speed comprehensive two-dimenstional gas chromatography/mass spectrometry." Awarded by:University of New South Wales, 2005. http://handle.unsw.edu.au/1959.4/39732.
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The use of short columns, higher carrier gas velocity and fast temperature programs in Comprehensive Two-Dimensional Gas Chromatography coupled to Time-of- Flight Mass Spectrometry (GC x GC/TOFMS) technique is expected to increase the speed of analysis up to several orders of magnitude when compared to conventional gas chromatography (GC) or gas chromatography/mass spectrometry (GC/MS). A systematic evaluation of the GC x GC/TOFMS configuration for high-speed applications has received little attention in the literature. The feasibility of High Speed Comprehensive Two-Dimensional Gas Chromatography coupled to Mass Spectrometry (High speed GC x GC/MS) for complex mixtures has been investigated in this thesis. A particular focus was placed on comparing conventional scanning quadrupole mass spectrometry (qMS) with a newly available non-scanning time-of-flight instruments (TOFMS). Experiments were carried out using GC/qMS, GC x GC/qMS, GC/TOFMS and GC x GC/TOFMS both in normal (slow) and fast temperature rates coupled with high frequency modulation in GC x GC. Initially a complex mixture consists of 24 semivolatile compounds was used as the analyte for the above purpose. In the initial experiments parameters like acquisition rate and duty cycle for qMS were determined to evaluate the effectiveness of the instrument for fast analysis. The practical duty cycle value obtained for the qMS was only about 18 % for single ion and one compound at a dwell time of 10 ms in SIM mode. In both high-speed GC/qMS and high-speed GC x GC/qMS techniques only about 40 % of the components in the complex mixture were found to be well separated. The acquisition rate of scanning instruments like qMS is incompatible for fast eluting peaks in high speed GC. TOFMS that has an acquisition rate of several hundred spectra per second offer the potential to define the fast GC peaks accurately. The high quality spectra from TOFMS also enable deconvolution of coeluting peaks in the complex mixtures. The advantage of the automated spectral deconvolution is demonstrated for the identification of the coeluting peaks in the complex mixtures. Coelution of peaks is also observed with highspeed GC/TOFMS technique. The high-speed GC x GC/TOFMS was also tested with two different analyte system ??? A pesticide mixture and platformate (an aromatic mixture) to evaluate the suitability for high-speed analysis of complex mixtures. A poor resolution was observed for the pesticide mixture in the two-dimensional plane and it appeared, as there was nearly no orthogonal separation in the second dimension. The platformate mixture displayed a better two-dimensional separation. Chromatographic peak resolution is not really a primary requirement for locating and identifying the coeluting compounds in high-speed GC x GC/TOFMS technique. However, it was observed that the high-speed GC x GC/TOFMS too faced problem to unscramble the mass spectra of those compounds with similar structure and sharing the same unique masses.
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Tian, Ming, and 田鸣. "Catalytic methane dehydroaromatization and polycyclic aromatic hydrocarbons formation on grain surface reaction studies using time of flight mass spectrometry." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/196032.
Full textAbstract:
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
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Middaugh, Joshua E. (Joshua Eugene). "The study of bimolecular radical reactions using a novel time-resolved photoionization time-of-flight mass spectrometry and laser absorption spectrometry apparatus." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87531.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
This thesis discusses my work to design, build, troubleshoot, and utilize a novel experimental apparatus that is capable of quantitatively measuring the concentrations of reacting gas-phase species and their reactive intermediates with sufficient time-resolution and sensitivity to determine both the kinetics and the product distributions of these systems. The apparatus uses laser absorption spectrometry to probe a radical of interest and thus measure its transient concentration quasi-continuously to precisely determine the kinetics of the reaction. At the same time, the apparatus samples the reactive mixture at various reaction times after the start of reaction to determine the time-resolved product distribution of the chemical system. This combination of techniques was used to study the reactions of vinyl radicals with alkenes, which are important reactions in incipient soot formation in combustion systems. Revised chemical kinetic rate coefficients and, for the first time, temperature- and pressure-dependent product branching fractions were experimentally measured for these reactions. In addition, a new potential energy surface for the vinyl + ethene reaction was calculated using state-of-the-art F12 quantum chemistry calculations, and the master equation for this reactive system was solved using various methods to determine the temperature- and pressure-dependent rate coefficients and product branching fractions.
by Joshua E. Middaugh.
Ph. D.
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Erb, William Joseph Owens Kevin G. "Exploration of the fundamentals of matrix assisted laser desorption/ionization time-of- flight mass spectrometry /." Philadelphia, Pa. : Drexel University, 2007. http://hdl.handle.net/1860/1765.
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