Rozprawy doktorskie: „Mass and Energy spectrometry”

1

Tsutsui, Yuko. "EXPLORING FUNCTIONAL AND FOLDING ENERGY LANDSCAPES BY HYDROGEN-DEUTERIUM EXCHANGE MASS SPECTROMETRY". Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1196199391.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

2

Fu, Tingting. "3D and High Sensitivity Micrometric Mass Spectrometry Imaging". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS218/document.

Pełny tekst źródła

Streszczenie:

L'imagerie par spectrométrie de masse est d’un grand intérêt pour aborder les questions biologiques en fournissant simultanément des informations chimiques et spatiales. En particulier, la spectrométrie de masse baptisée TOF-SIMS est bien reconnue par sa haute résolution spatiale (< 1 μm), qui est essentielle pour révéler l'information chimique dans une zone submicronique. L'emploi croissant de cette technique dans la caractérisation des échantillons biologiques a bénéficié du développement de nouvelles sources d'ions d’agrégats. Cependant, les processus d'ionisation/désorption des analytes sous les impacts d’agrégats lourds sont encore mal compris. D'un autre côté, techniquement, les instruments TOF-SIMS commerciaux actuels ne peuvent pas fournir une résolution en masse suffisante ni une précision sur la détermination de la masse pour l'identification moléculaire, ce qui rend les analyses de systèmes biologiques complexes très difficiles, et nécessite le recours à la fragmentation MS/MS. Cette thèse vise à mieux comprendre la production d'ions sous l’impact d’agrégats lourds et à explorer la capacité MS/MS du spectromètre de masse par temps de vol combiné à l’imagerie ionique en utilisant le spectromètre de masse PHI nanoTOF II. Ce dernier point a été réalisé en cartographiant en haute résolution spatiale des métabolites importants de bois. Pour comprendre la production d'ions sous les impacts d’agrégats d'argon massifs, l'énergie interne des ions secondaires a été mesurée en utilisant la mesure du taux de survie d'une série d'ions benzylpyridinium. L'étude de diverses conditions d'impact (énergie, vitesse, taille des agrégats) a montré que la vitesse joue le rôle majeur dans la distribution d'énergie interne et la fragmentation moléculaire dans le régime à faible énergie par atome (E/n < 10 eV).Les capacités de la fragmentation MS/MS et d'imagerie en parallèle du spectromètre PHI nanoTOF II nouvellement conçu ont été évalués par cartographie MS/MS in situ des métabolites bioactifs rubrynolide et rubrenolide dans les espèces amazoniennes de bois Sextonia rubra, ainsi qu’une identification in situ des métabolites précurseurs. L'imagerie TOF-SIMS 2D et 3D a permis de localiser les cellules où cette biosynthèse s’effectue. Les résultats ont conduit à la proposition d'une voie possible de biosynthèse des deux métabolites. Pour étendre l'application de l'imagerie TOF-SIMS dans l'analyse chimique du bois, la distribution radiale des extraits de bois dans le duramen du bois du mélèze européen a également été étudiée
Mass spectrometry imaging has been shown of great interest in addressing biological questions by providing simultaneously chemical and spatial information. Particularly, TOF-SIMS is well recognized for its high spatial resolution (< 1 µm) which is essential in disclosing chemical information within a submicron area. The increasing use of TOF-SIMS in characterizing biological samples has greatly benefited from the introduction of new cluster ion sources. However, the ionization/desorption of the analytes under impacts of large clusters is still poorly understood. On the other hand, technically, current commercial TOF-SIMS instruments generally cannot provide sufficient mass resolution or mass accuracy for molecular identification, making analyses of complex biological systems especially challenging when no MS/MS fragmentation is available. Thus this thesis is aimed to get a better understanding of ion production under cluster impacts, to explore the MS/MS capability of the parallel imaging MS/MS Spectrometer (PHI nanoTOF II), as well as to apply TOF-SIMS to map important wood metabolites with high spatial resolution.In order to understand ion production under impacts of massive argon clusters, internal energy distributions of secondary ions were measured using survival yield method which involves the analyses of a series of benzylpyridinium ions. Investigation of various impacting conditions (energy, velocity, cluster size) suggested that velocity of the clusters play a major role in internal energy distribution and molecular fragmentation in the low energy per atom regime (E/n < 10 eV). The MS/MS fragmentation and parallel imaging capabilities of the newly designed PHI nanoTOF II spectrometer were evaluated by in situ MS/MS mapping of bioactive metabolites rubrynolide and rubrenolide in Amazonia wood species Sextonia rubra. Then this parallel imaging MS/MS technique was applied to perform in situ identification of related precursor metabolites in the same tree species. 2D and 3D TOF-SIMS imaging were carried out to target the plant cells that biosynthesize rubrynolide and rubrenolide. The results led to the proposal of a possible biosynthesis pathway of these two metabolites. In addition, to expand the application of TOF-SIMS imaging in wood chemistry analysis, radial distribution of wood extractives in the heartwood of European larch was also investigated

Style APA, Harvard, Vancouver, ISO itp.

3

Rowland, Tyson G. "Accurate ionic bond energy measurements with TCID mass spectrometry and imaging PEPICO spectroscopy". Scholarly Commons, 2012. https://scholarlycommons.pacific.edu/uop_etds/809.

Pełny tekst źródła

Streszczenie:

Two projects are presented here. In the first, metal-cyclopentadienyl bond dissociation energies (BDEs) were measured for seven metallocene ions (Cp2M+, Cp = η5-cyclopentadienyl = c-C5H5, M = Ti, V, Cr, Mn, Fe, Co, Ni) using threshold collision-induced dissociation (TCID) performed in a guided ion beam tandem mass spectrometer. For all seven room temperature metallocene ions, the dominant dissociation pathway was simple Cp loss from the metal. Traces of other fragment ions were also detected, such as C10H10+, C10H8+, C8H8+, C3H3+, H2M+, C3H3M+, C6H6M+, and C7H6M+, depending on the metal center. Statistical modeling of the Cp-loss TCID experimental data, including consideration of energy distributions, multiple collisions, and kinetic shifts, allow the extraction of 0 K [CpM+ - Cp] BDEs. These are found to be 4.95 ± 0.15, 4.02 ± 0.14, 4.22 ± 0.13, 3.51 ± 0.12, 4.26 ± 0.15, 4.57 ± 0.15, and 3.37 ± 0.12 eV for Cp2To+, Cp2V+, Cp2Cr+, Cp2Mn+, Cp2Fe+, Cp2Co+, and Cp2Ni+, respectively. The measured BDE trend is largely in line with arguments based on a simple molecular orbital picture, with the exceptions of a reversal in Cp2Mn+ and Cp2Ni+ BDEs (although within uncertainty), and the exceptional case of titanocene, most likely attributable to its bent structure. The new results presented here are compared to previous literature values and are found to provide a more complete and accurate set of thermochemical parameters. In the second project, imaging photoelectron photoion coincidence (iPEPICO) spectroscopy has been used to determine 0 K appearance energies for the unimolecular dissociation reactions of several energy selected 1-alkyl iodide cations n-CnH2n+1I+ → CnH2n+1+ + I, (n = 2-5). The 0 K appearance energies of the iodine-loss fragment ions were determined to be 9.836 ± 0.010, 9.752 ± 0.010, 9.721 ± 0.010, and 9.684 ± 0.010 eV for n-C3H7I, n-C4H9I, n-C5H11I, and n-C6H13I molecules, respectively. Isomerization of then-alkyl iodide structures into 2-iodo species adds complexity to this study. Using literature adiabatic ionization energies, ionic bond dissociation energies were calculated for the four modeled iodoalkyl cations and it was shown that as the alkyl chain length increases, the carbon-halogen bond strength decreases, supporting the suggestions set forth by inductive effects. In the modeling with statistical energy distributions and rate theory, the role of hindered rotors was also evaluated and no strong experimental evidence was found either way. The heaviest species in the series, heptyl iodide (C7H15I) was also measured via iPEPICO and showed to have a greater complexity of fragmentation than the lighter analogs. Sequential dissociation of the first fragment ion, C7H15+ leads to C4H9+, C5H11+, and C3H7+ ions in competitive dissociation processes, dominated at low energies by the C4H9+ cation.

Style APA, Harvard, Vancouver, ISO itp.

4

Begley, Ian S. "A study of isotope ratio measurement by inductively coupled plasma mass spectrometry". Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/12223.

Pełny tekst źródła

Streszczenie:

The measurement of isotopic ratios by inductively coupled plasma mass spectrometry (ICP-MS) has the benefits of ionising all metallic elements, simplifying sample preparation and reducing analysis time, when compared with thermal ionisation mass spectrometry (TIMS). However, the use of ICP-MS in isotopic ratio studies has been somewhat restricted by Its failure to offer the precision and accuracy required by a variety of applications. The precision achievable by ICPMS, typically 0.2 to 0.3 % RSD, for isotopic ratios, has generally been regarded as being primarily limited by instrumental instability. An investigation of the sources of instrumental noise in ICP-MS has been undertaken, utilising noise spectral analysis as a diagnostic md Study of parametric variation upon noise production has identified the methods by which modulation of the ion signal occurs Noise spectral analysis has allowed an understanding of the limitations imposed upon measurement precision by the various contributing noise sources to be established The key to improved measurement precision has been found to lie in the development of data acquisition methods which allow the predominant sources of instrumental noise to be effectively filtered from the ion signal The methodology developed for sequential measurement of isotopes, using a quadrupole mass analyser, to reduce the deleterious influences of instrumental noise is discussed. Results are given for isotopic ratio measurement which demonstrate that a precision of approximately 0 05 % RSD can be attained The factors which affect the accuracy of isotopic ratio measurement are shown to be many and varied and depend to a large extent on the particular Isotopes bemg studied Definition of an appropriate measurement strategy for high accuracy isotope ratio measurement involves consideration of all possible causes of bias and adoption of methods for their elimination or correction. To facilitate this process a protocol has been developed and subsequently applied to various elements and instrument systems.

Style APA, Harvard, Vancouver, ISO itp.

5

Sassin, Nicholas A. "Optical and collisional energy transfer processes in fluorescent dyes, quaternary alkylammonium and peptide cations". abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3307572.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

6

Smith, Lori Lyn. "Effectiveness of low energy collisional activation methods for automated peptide sequencing by tandem mass spectrometry". Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280450.

Pełny tekst źródła

Streszczenie:

The relative efficiencies of low energy (< 100 eV) collisional activation techniques were determined for peptide sequencing by tandem mass spectrometry (MS/MS). Tryptic peptides were fragmented using either collision induced dissociation (CID) or surface induced dissociation (SID) to generate spectral databases. Statistical analysis of the resulting fragment ions and success rates for automated peptide sequencing by publicly available algorithms provided a measure of the value of sequencing information content of CID and SID MS/MS spectra. Typical success rates were determined for automated sequencing by SEQUEST¹⁻³, MS-Tag⁴, Mascot's⁵ MS/MS Ion Search and Sequence Query using low energy CID spectra. The ability of an algorithm to match peptide sequences to raw MS/MS data directly depended on various factors including the mass spectrometer from which the spectra were acquired, the precursor ion charge state, and the mass accuracy and resolution available in the spectra. Statistical analysis demonstrated the presence of similar fragment ions in SID and CID spectra. A lack of long contiguous ion series in SID spectra prevented automated sequencing using conventional approaches. Thus, "patchwork peptide sequencing"⁶, an unconventional method to derive specific sequence criteria for unknown peptides from SID spectra, was performed. Submitting this information to Mascot's Sequence Query allowed database searching strategies to achieve automated peptide sequencing with SID spectra. Some aspects of gas phase ion chemistry were explored for the unexpected formation of fragment ions from cleavage C-terminal to proline residues. Semi-empirical calculations suggest the most stable structure for valineprolyl-b₂ ion is a diketopiperazine, although the MS/MS/MS fragmentation pattern for VP-b₂ is indicative of an oxazalone structure. Support for a diketopiperazine structure is provided by similar fragmentation patterns for VP-b₂ and a synthetic diketopiperazine VP, and prevention of the formation of VP-b₂ by acetylation of the free N-terminus. Substitution of N-methyl alanine for proline produces a b₂ ion that fragments by loss of a portion of the valine residue, consistent with an oxazalone structure. However, theoretical calculations suggest the N-methyl alanine-containing b₂ ion is a diketopiperazine. The differences in fragmentation patterns indicate that the gas phase ion structures for the proline- and N-methyl alanine-containing b₂ ions are different, although stability calculations suggest otherwise.

Style APA, Harvard, Vancouver, ISO itp.

7

Yau, Pui Yip. "Thresholds for production of gaseous ions in matrix-assisted laser desorption/ionisation mass spectrometry of bio-molecules". Thesis, University of Warwick, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389459.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

8

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.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

9

Bottrill, Andrew R. "High-energy collision-induced dissociation of macromolecules using tandem double-focusing/time-of-flight mass spectrometry". Thesis, University of Warwick, 2000. http://wrap.warwick.ac.uk/52318/.

Pełny tekst źródła

Streszczenie:

The first part of this study involves the adaptation of a matrix-assisted laser desorption/ionisation (MALDI) ion source for a tandem double-focusingltime-offlight instrument (MAG-TOF). Ion trajectory modelling was carried out for defining the optimum ion optical configuration for a new extraction region and associated ion optics that were designed and constructed. Installation of the new ion source resulted in increased sensitivity and no loss of resolution. The second part of this study involves the analysis of fullerenes and fullerene derivatives by high-energy collision-induced dissociation (CID). The structure of fullerenes formed by coalescence under the conditions of laser desorption were shown to be that of a single fullerene closed-cage structure. The dissociation of exohedral fullerene hydride derivatives was investigated. The third part of this study investigates the high-energy collision-induced dissociation of polyglycol polymer ions generated by MALDI. Mechanisms have been proposed for the dissociation of poly(ethylene glycol) and poly(propylene glycol). High-energy CID has been shown to be particularly useful for the determination of polymer end-group structure.

Style APA, Harvard, Vancouver, ISO itp.

10

Williams, Jonathan Paul. "Ion structure determination using novel time-of-flight techniques and mass-analysed ion kinetic energy spectrometry". Thesis, Swansea University, 2000. https://cronfa.swan.ac.uk/Record/cronfa42653.

Pełny tekst źródła

Streszczenie:

Mass spectrometry is a powerful analytical technique that possesses the capability of molecular characterisation of complex mixtures. The technique has been the method afforded in this study for the characterisation of such mixtures of industrial relevance. The last decade has seen an important revival of one area in particular, time-of-flight mass spectrometry, which has had a significant impact on the field of mass spectrometry. This has been largely due to two recently developed ionisation methods, namely electrospray and matrix-assisted laser desorption ionisation. These ionisation methods have led to the development of novel time-of-flight mass spectrometer designs by commercial manufacture's, which take advantage of the theoretically unlimited mass range and the acquisition of a full mass spectrum every injection pulse of ions. Matrix-assisted laser desorption and electrospray ionisation have been interfaced to two novel time-of-flight mass analysers, the 'Autospec' oa- ToF, a hybrid sector orthogonal-acceleration time-of-flight instrument and the 'LCT', a liquid chromatograph time-of-flight instrument, manufactured by Micromass U.K., Ltd respectively. They have been successfully used to investigate and fully characterise complex systems of industrial significance. The 'Autospec' oa-ToF was used for high-energy collision induced dissociation experiments. The high sensitivity of the time-of-flight analyser was very powerful in the detection of product ions produced from various synthetic polymer precursor ions. The detailed structural information produced will be shown to fully characterise the polystyrene samples studied. An expanding area of mass spectrometry is electrospray ionisation used with orthogonal acceleration time-of-flight. The two methods when used in reflectron mode have significantly removed early limitations on resolution that time-of-flight mass analysers initially possessed. Sampling the electrosprayed ions orthogonally results in an increased duty cycle, which can be advantageous if fast chromatography is required. Evaluation of the LCT instrument, will be shown to provide mass resolution of the order of 5000 at full-width half maximum, mass accuracies of the order of 5ppm, full scan sensitivity equal to that of a quadrupole instrument in single ion monitoring mode and the detection of singly charged ions greater than m/z 10000. The research unit at Swansea University allowed the opportunity to investigate ion structural problems on an instrument built in house of BEE geometry. The energy released upon metastable fragmentation, leading to the formation of C3H3+ ions formed in some simple organic molecules yield peak shapes of a composite nature. The selection of ions from the translational energy-release distribution produced, have been investigated by consecutive reactions and will be shown to fully characterise isomeric ion structures.

Style APA, Harvard, Vancouver, ISO itp.

11

Saraswat, Suraj. "Investigation of Energy Transfer, Quantification, and Localization of Peptides and Proteins by Fluorescence Spectroscopy and Mass Spectrometry". University of Toledo / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1341599821.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

12

Treufeld, Imre. "I. Polymer Films for High Temperature Capacitor ApplicationsII. Differential Electrochemical Mass Spectrometry". Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1465503063.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

13

Angelico, Vincent James. "The development of a mass spectrometry-based technique that uses low energy ion-surface collisions to characterize surfaces". Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280148.

Pełny tekst źródła

Streszczenie:

Low energy (tens of eV) ion-surface collisions carried out in a tandem mass spectrometer are investigated as a tool to characterize self-assembled monolayer (SAM) films. The target films are prepared by spontaneous chemisorption of thiol-based (HS-R) compounds onto Au (111) substrates. Most of the films used as targets contain alkane or fluoro-alkane backbones, some with unique groups in the terminal position (e.g., -CD₃, -OH, -OC(O)CF₃). Pyrazine is the most frequently used probe ion, however in certain cases other small organic molecules are also used. Common interactions between the impinging ion and the target film that vary as a function of film characteristics include, but are not limited to, reactive scattering, neutralization and T → V conversion. Pyrazine ion readily reacts when colliding with hydrocarbon films at 20-eV, forming product ions that incorporate a hydrogen atom or a methyl group. Several examples of the utility of these processes to characterize film properties are presented. For hydrocarbon films, ion-surface reactions of pyrazine ion resulting in addition of a hydrogen atom or a methyl group are shown to vary with the quality, chemical composition and orientation of the target film. Experiments with isotopically labeled films show that the ion beam interacts predominantly with the end groups of the film, however interactions with underlying groups increase as the film or substrate quality decreases. The orientation difference of odd and even chain length n-alkanethiols produces a measurably different degree of hydrogen addition with the higher free energy odd chain length orientation being more reactive. The composition of mixed component films (H, D or H, F) is tracked by measuring the abundance of unique reaction products, energy transfer (translational to vibrational conversion) and charge exchange properties. When mixed films containing deuterium labeled and unlabeled n-alkanethiols are subjected to collisions of 20-eV pyrazine ion, the D-addition ion abundance increases linearly with the surface concentration of D-containing alkane chains. When mixed films containing different ratios of H and F components are the target, several processes track with the changing population of surface species. As the target films become more fluorocarbon in nature H-addition decreases, total ion current reaching the detector increases, and dissociation increases. Several properties of electron transfer from the film to the ion are examined. When the probe ion and collision energy remain consant, charge exchange is shown to be primarily governed by the work function of the film and the thickness of the adsorbed layer. Fluorocarbon films, which have a higher work function than hydrocarbon films, consistently show less charge exchange. When comparing hydrocarbon films of varying chain lengths (ranging from 15 to 18 carbons), a increase of ∼1% in total ion current measured at the detector is observed for each additional methylene in the chain.

Style APA, Harvard, Vancouver, ISO itp.

14

Al-Qahtani, Khalid Mohammad. "Developing liquid chromatography-mass spectrometry strategies for investigating energy metabolism with application to isocitrate dehydrogenase mutations in cancer : development and application of methods for qualitative and quantitative analysis of TCA cycle metabolites using liquid chromatography coupled to mass spectrometry". Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:354009b1-30a5-43a0-bbf1-5907437ea53a.

Pełny tekst źródła

Streszczenie:

Isocitrate dehydrogenases (IDHs) act in the tricarboxylic acid (TCA) cycle to catalyse the conversion of isocitrate to 2-oxoglutarate (2-OG) with concomitant production of NADH and/or NADPH. In humans, mutations causing IDH1 and IDH2 substitutions have been found during DNA sequencing of human glioblastomas. Some cancerassociated IDH mutations promote the reduction of 2-OG to give D-2-hydroxyglutarate (D-2-HG) a chiral, polar dicarboxylic acid. Investigations on the underlying links between 2-HG and cancer require sensitive methods for monitoring IDH1 and IDH2 activities. The reported LC/MS methods for the analysis of TCA cycle metabolites are limited in term of their accuracy and ability to identity isomers. Methods for the direct measurement of levels of TCA cycle and associated metabolites using mass spectrometry based metabolomics are desired. However, for the reported methods, the limits of detection are often prohibitive; they are normally suited for the investigation of known metabolites rather than for the discovery of new compounds. With some exceptions, the existing methods have not been extensively validated, e.g. with respect to limits of detection and quantification as well as precision. The main aim of the research presented in this thesis was to develop methods for TCA cycle metabolite analysis in cells and to apply these methods to investigations on variant IDH enzymes. A range of LC-MS approaches were investigated including: (1) C18 reversed phase chromatography of non-derivatised TCA cycle metabolites, (2) ion paring chromatography, and (3) mixed mode chromatography with either MS, or isotope ratio mass spectrometry detection, gas chromatography of TBDMS derivatised TCA cycle metabolites. Analysis of the elution patterns for these separation techniques enabled estimation of the retention parameters of TCA cycle metabolites and investigations on their metabolism. The most sensitive approach developed employed mixed mode chromatography coupled to isotope ratio mass spectrometry, which was optimised for the analysis of TCA cycle metabolites. This was shown to have a limit of detection two orders of magnitude lower (4μM) than more conventional mass spectrometry techniques. Using 13C-[4C]-Aspartate labelling in cell culture, a quantification protocol was developed which employed a non-labelled internal standard and selectively labelled cell culture. The method was shown to be suitable for both very accurate quantification at low concentration levels and metabolic studies. The analytical methods developed for TCA cycle metabolites analysis were successfully applied to the analysis of 2-OG and D-2-HG metabolism. The stereochemistry of 2-HG in the cell pellets as well as of the citrate/isocitrate isomers was investigated. IDH1R132H was shown to catalyse reduction of 2-OG resulting in D-2-HG. TCA cycle analysis was used in order to investigate 2-OG and 2-HG metabolism related to IDH1R132H. Using the method developed for the analysis of non-derivatised TCA cycle intermediates, the screening of potential substrates of IDH1R132H was carried out. The isotope ratio mass spectrometry protocol was applied to the study of IDH1R132H in cell culture; levels of D-2-HG were quantified. The analytical methods described complement the established metabolomics techniques. The methods developed enable the investigation into the regio- and stereo- chemistry of TCA cycle and associated metabolites and are powerful tools for investigating cancer cell metabolism.

Style APA, Harvard, Vancouver, ISO itp.

15

Yang, Xi. "Characterization of Self-Assembled Monolayers by Low Energy Reactive Ion Scattering: Influences of Terminal Group Composition and Structure on Ion-Surface Interaction". Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/195240.

Pełny tekst źródła

Streszczenie:

Low energy (tens of eV) polyatomic cations were used as probes for characterization of monolayers of spontaneously chemisorbed thiols on gold. Characteristics including chemical composition, surface order and orientation of the self-assembled monolayers (SAMs) can be derived by monitoring the products of projectile ion neutralization, surface-induced dissociation (SID), and ion-surface reactions.To study the influence of the terminal group chemical structures and orientations of the SAMs on ion-surface interactions, a series of semi-fluorinated alkane thiols with difluoromethylenes buried underneath hydrocarbon terminal groups were examined (CH3CF2CH2− and CH3CH2CF2−). Compared to terminally fluorinated SAMs, they showed more projectile ion neutralization and less internal to vibrational energy deposition into precursor ions. Projectile ion-hydrocarbon reactions decreased significantly when difluoromethylenes are one or two bonds away from the terminal group. Furthermore, ion-surface reaction results on surfaces with odd and even chain lengths suggested that they have similar terminal methyl orientations to their hydrocarbon counterparts.Mixed monolayers of CF3CF2(CH2)14SH (F-SAMs) and CH3(CH2)15SH (H-SAMs) with systematically changing electron transfer, energy deposition and ion-surface reaction were prepared using mixed thiols solution and micro-contact printing (μ-CP). The solution mixture system showed linear variations in electron transfer and energy deposition with different F-SAM surface concentrations, while non-linear changes occur for ion-surface reaction suggesting strong lateral interactions between the two components. These interactions are minimized in the μ-CP system containing domains of each thiol. Energy deposition on the patterned surfaces varies non-linearly with changing F-SAM concentration which differs from the homogenously mixed system.To explore SID with a 90 collision angle, eV SID of a series of protonated peptide ions were performed in an in-line sector Time-Of-Flight (TOF) mass spectrometer. The results were compared to keV collision-induced dissociation (CID) data collected with the same instrument. Fragmentation efficiency for SID was higher than CID for those peptides. In addition to the excellent control over laboratory collision energies with SID, different amount of energy deposition can be achieved when varying surface composition, e.g. using mixed F-SAM/H-SAM.Reactive ion scattering spectrometry (RISS) results provided more in-depth knowledge of low energy ion-surface interactions that will promote usage of RISS as a novel surface characterization technique.

Style APA, Harvard, Vancouver, ISO itp.

16

Naylor, J. C. "The study of sputtering by concentration modulated absorption spectroscopy and the study of internal energy effects on collision induced decomposition mass spectrometry". Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638299.

Pełny tekst źródła

Streszczenie:

The measurement of the absolute concentration of sputtered neutrals from a metal Li surface and polycrystalline NaC1 target has been achieved using the technique of concentration modulated absorption spectroscopy. The dependence of the amount sputtered on the target temperature, ion energy and target density has been investigated. The atomic density of the plume has been mapped in two dimensions under varying sputtering conditions. Utilising a previous theory describing a radial sputter distribution function the experiments have yielded values for the sputter yield of lithium and sodium. The profiling of sputtered neutrals across a planar glow discharge under varying cell conditions and discharge gases has been achieved using the laser spectroscopic technique. These experiments show that the sticking coefficient, α, of Li atoms on Li metal is non-unity. The experiments have been fitted using a Monte-Carlo model to generate values of α. An analytical model has also been developed to fit the experimental data. The model yields useful physical parameters concerning the plasma. This includes sticking coefficient data. The model has been compared with the computer-based method. High-energy collision induced decomposition mass spectrometry has been to investigate the possible effect of the internal energy of the precursor ion on the appearance of the spectra. Deuterated ethanol and the protonated deuterium counterpart were specifically produced in the ion source isomerically pure and to eliminate the presence of isotope scrambling. The experiments show that the spectra do vary significantly depending on the reaction conditions of temperature and pressure under which the protonated ethanol or the deuterated equivalent is produced.

Style APA, Harvard, Vancouver, ISO itp.

17

Zhang, Yifan. "Metabolic Energy Balances in Ketotic Rat Brain". Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1370371336.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

18

Mahdi, A. M. "A mass spectrometric study of translational energy release in the reactions of gas phase cations". Thesis, University of Essex, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379376.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

19

Hennemann, Bruno Luís. "Energia de interação cátion-ânion de líquidos iônicos dicatiônicos em fase gasosa". Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/11976.

Pełny tekst źródła

Streszczenie:

Electrospray ionization mass spectrometry (ESI-MS) with induced collision energy was used to carry out a comprehensive study on the interaction energies between cations and anions of dicationic ionic liquids. The influence of the anion ([Br]-, [NO3]-, [BF4]-, [SCN]- and [Cl]-) and the size of alkyl chain (n = 4,6,8 and 10) in the interaction energy of ionic liquids derived from the 1, n-bis (3-methylimidazolyl-1-yl) alkane with n = 4,6,8 and 10, in the gas phase was investigated. Three experiments were carried out to determine the cation-anion interaction energy: (i) ESI-MS of binary (1:1) mixtures of ionic liquids with different anions or cations; (Ii) ESI-MS of ionic liquid individually with variation of the applied collision energy and determination of the center of mass energy (Ecm) using the relation between the intensity of the precursor ion and the sum of the ions; (iii) the rate of variation of the intensity of the precursor ion as a function of collision energy at different concentrations of all ionic liquids was obtained. From this correlation, the cation-anion dissociation constant of the dicationic ionic liquids was obtained. The results showed the appearance of mixed species (example: [Bis-C8(MIM)22XY]- and [C8(MIM)XY]-) in the binary mixtures. The application of the induced collision energy in the mixtures allowed estimating which anion interacts more effectively with the cation. Also for this experiments, the dicationic ionic liquids with the anions [Cl]-, [Br]- and [NO3]- presented higher cation-anion interaction energy. The increasing order of interaction energy was [BF4]- <[SCN]- <[NO3]- <[Br]- <[Cl]-. The Ecm values for ionic liquids with different anions did not indicate trends in the interaction energy in relation to structural factors such as ionic radius and molecular volume. Thus, for the anions, it was found that the interaction increases in the following order: [SCN]- <[Cl]- <[NO3]- <[Br]- <[BF4]-. On the other hand, increasing the size of the spacer alkyl chain caused an increase in cation-anion interaction energy. As the concentration of the ionic liquid increased, an increase in the precursor ion intensity was observed.
A espectrometria de massa com ionização por electrospray (ESI-MS) com energia de colisão induzida foi utilizada para realizar um estudo compreensivo sobre as energias de interação entre cátions e ânions de líquidos iônicos dicatiônicos. Foi avaliada a influência do ânion ([Br]-, [NO3]-, [BF4]-, [SCN]- e [Cl]-) e o tamanho da cadeia alquílica espaçadora (n=4,6,8 e 10) na energia de interação dos líquidos iônicos dicatiônicos, derivados do 1,n-bis(3-metilimidazolil-1-íneo)alcano em fase gasosa. Três experimentos foram realizados para a determinação da energia de interação cátion-ânion: (i) ESI-MS de misturas binárias (1:1) de líquidos iônicos com diferentes ânions ou cátions; (ii) ESI-MS de cada líquido iônico individualmente com variação da energia de colisão aplicada e determinação da energia de centro de massa (Ecm) usando a relação entre intensidade do íon precursor e somatório dos íons. (iii) Por fim, foi obtida a taxa de variação da intensidade do íon precursor em função energia de colisão de todos os líquidos iônicos. A partir desta correlação, foi obtida a constante de dissociação cátion-ânion dos líquidos iônicos dicatiônicos. Os resultados mostraram o aparecimento de espécies mistas (exemplo: [Bis-C8(MIM)22XY]- e [C8(MIM)XY]-) nos experimentos das misturas. A aplicação da energia de colisão induzida nas misturas também permitiu estimar qual ânion interage mais efetivamente com o cátion. Ainda para este experimentos, os líquidos iônicos dicatiônicos com os ânions [Cl]-, [Br]- e [NO3]- apresentaram maior energia de interação cátion-ânion. A escala em ordem crescente de energia de interação foi [BF4]-< [SCN]- < [NO3]- < [Br]- < [Cl]-. Os valores de Ecm para os líquidos iônicos com diferentes ânions não indicou tendências na energia de interação em relação fatores estruturais tais como raio iônico e volume molecular. Dessa forma, para os ânions, foi encontrado que a interação aumenta na seguinte ordem: [SCN]-<[Cl]-<[NO3]-<[Br]-<[BF4]-. Por outro lado, o aumento do tamanho da cadeia alquílica espaçadora causou um aumento na energia de interação cátion-ânion. Com o aumento da concentração do líquido iônico, foi observado um aumento na intensidade do íon precursor.

Style APA, Harvard, Vancouver, ISO itp.

20

Wishart, Cornelia. "Measurement of total body water (TBW) and total energy expenditure (TEE) using stable isotopes". Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/44135/1/Cornelia_Wishart_Thesis.pdf.

Pełny tekst źródła

Streszczenie:

Understanding the relationship between diet, physical activity and health in humans requires accurate measurement of body composition and daily energy expenditure. Stable isotopes provide a means of measuring total body water and daily energy expenditure under free-living conditions. While the use of isotope ratio mass spectrometry (IRMS) for the analysis of 2H (Deuterium) and 18O (Oxygen-18) is well established in the field of human energy metabolism research, numerous questions remain regarding the factors which influence analytical and measurement error using this methodology. This thesis was comprised of four studies with the following emphases. The aim of Study 1 was to determine the analytical and measurement error of the IRMS with regard to sample handling under certain conditions. Study 2 involved the comparison of TEE (Total daily energy expenditure) using two commonly employed equations. Further, saliva and urine samples, collected at different times, were used to determine if clinically significant differences would occur. Study 3 was undertaken to determine the appropriate collection times for TBW estimates and derived body composition values. Finally, Study 4, a single case study to investigate if TEE measures are affected when the human condition changes due to altered exercise and water intake. The aim of Study 1 was to validate laboratory approaches to measure isotopic enrichment to ensure accurate (to international standards), precise (reproducibility of three replicate samples) and linear (isotope ratio was constant over the expected concentration range) results. This established the machine variability for the IRMS equipment in use at Queensland University for both TBW and TEE. Using either 0.4mL or 0.5mL sample volumes for both oxygen-18 and deuterium were statistically acceptable (p>0.05) and showed a within analytical variance of 5.8 Delta VSOW units for deuterium, 0.41 Delta VSOW units for oxygen-18. This variance was used as “within analytical noise” to determine sample deviations. It was also found that there was no influence of equilibration time on oxygen-18 or deuterium values when comparing the minimum (oxygen-18: 24hr; deuterium: 3 days) and maximum (oxygen-18: and deuterium: 14 days) equilibration times. With regard to preparation using the vacuum line, any order of preparation is suitable as the TEE values fall within 8% of each other regardless of preparation order. An 8% variation is acceptable for the TEE values due to biological and technical errors (Schoeller, 1988). However, for the automated line, deuterium must be assessed first followed by oxygen-18 as the automated machine line does not evacuate tubes but merely refills them with an injection of gas for a predetermined time. Any fractionation (which may occur for both isotopes), would cause a slight elevation in the values and hence a lower TEE. The purpose of the second and third study was to investigate the use of IRMS to measure the TEE and TBW of and to validate the current IRMS practices in use with regard to sample collection times of urine and saliva, the use of two TEE equations from different research centers and the body composition values derived from these TEE and TBW values. Following the collection of a fasting baseline urine and saliva sample, 10 people (8 women, 2 men) were dosed with a doubly labeled water does comprised of 1.25g 10% oxygen-18 and 0.1 g 100% deuterium/kg body weight. The samples were collected hourly for 12 hrs on the first day and then morning, midday, and evening samples were collected for the next 14 days. The samples were analyzed using an isotope ratio mass spectrometer. For the TBW, time to equilibration was determined using three commonly employed data analysis approaches. Isotopic equilibration was reached in 90% of the sample by hour 6, and in 100% of the sample by hour 7. With regard to the TBW estimations, the optimal time for urine collection was found to be between hours 4 and 10 as to where there was no significant difference between values. In contrast, statistically significant differences in TBW estimations were found between hours 1-3 and from 11-12 when compared with hours 4-10. Most of the individuals in this study were in equilibrium after 7 hours. The TEE equations of Prof Dale Scholler (Chicago, USA, IAEA) and Prof K.Westerterp were compared with that of Prof. Andrew Coward (Dunn Nutrition Centre). When comparing values derived from samples collected in the morning and evening there was no effect of time or equation on resulting TEE values. The fourth study was a pilot study (n=1) to test the variability in TEE as a result of manipulations in fluid consumption and level of physical activity; the magnitude of change which may be expected in a sedentary adult. Physical activity levels were manipulated by increasing the number of steps per day to mimic the increases that may result when a sedentary individual commences an activity program. The study was comprised of three sub-studies completed on the same individual over a period of 8 months. There were no significant changes in TBW across all studies, even though the elimination rates changed with the supplemented water intake and additional physical activity. The extra activity may not have sufficiently strenuous enough and the water intake high enough to cause a significant change in the TBW and hence the CO2 production and TEE values. The TEE values measured show good agreement based on the estimated values calculated on an RMR of 1455 kcal/day, a DIT of 10% of TEE and activity based on measured steps. The covariance values tracked when plotting the residuals were found to be representative of “well-behaved” data and are indicative of the analytical accuracy. The ratio and product plots were found to reflect the water turnover and CO2 production and thus could, with further investigation, be employed to identify the changes in physical activity.

Style APA, Harvard, Vancouver, ISO itp.

21

Solders, Andreas. "Precision mass measurements : Final limit of SMILETRAP I and the developments of SMILETRAP II". Doctoral thesis, Stockholms universitet, Fysikum, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-56777.

Pełny tekst źródła

Streszczenie:

The subject of this thesis is high-precision mass-measurements performed with Penning trap mass spectrometers (PTMS). In particular it describes the SMILETRAP I PTMS and the final results obtained with it, the masses of 40Ca and that of the proton. The mass of 40Ca is an indispensible input in the evaluation of measurements of the bound electron g-factor, used to test quantum electrodynamical calculations in strong fields. The value obtained agrees with available literature values but has a ten times higher precision. The measurement of the proton mass, considered a fundamental physical constant, was performed with the aim of validating other Penning trap results and to test the limit of SMILETRAP I. It was also anticipated that a measurement at a relative precision close to 10-10 would give insight in how to treat certain systematic uncertainties. The result is a value of the proton mass in agreement with earlier measurements and with an unprecedented precision of 1.8×10-10. Vital for the achieved precision of the proton mass measurement was the use of the Ramsey excitation technique. This technique, how it was implemented at SMILETRAP I and the benefits from it is discussed in the thesis and in one of the included papers. The second part of the thesis describes the improved SMILETRAP II setup at the S-EBIT laboratory, AlbaNova. All major changes and upgrades compared to SMILETRAP I are discussed. This includes, apart from the Ramsey excitation technique, higher ionic charge states, improved temperature stabilization, longer run times, different reference ions, stronger and more stable magnetic field and a more efficient ion detection. Altogether these changes should reduce the uncertainty in future mass determinations by an order of magnitude, possibly down to 10-11.
At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 9: Accepted.

Style APA, Harvard, Vancouver, ISO itp.

22

Al, Mahmoud Alsheikh Amer. "Modelování chemických procesů". Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2015. http://www.nusl.cz/ntk/nusl-233403.

Pełny tekst źródła

Streszczenie:

V této práci je prezentována studie fragmentačního procesu zvolené molekuly a jeho vztah ke složení fragmentačních produktů. Práce je zaměřená na výpočet fragmentační energie molekuly pomocí ab initio kvantově chemických metod, metodou „density functional theory (DFT)“ a také srovnáním s experimentem. Je prezentován vliv výpočetní metody, bázového setu, a geometrie molekuly na simulaci. Byla porovnána fragmentace methylfenylsilanu (MPS), dimethylfenylsilanu (DMPS), a trimetylfenylsilanu (TMPS). Fragmentace byla iniciována monochromatickým elektronovým svazkem (EII). Hmotnostní spektrometrie byla využita ke studiu složení fragmentačních produktů MPS a TMPS. Fragmentační produkty MPS a TMPS měřené v rámci této práce byly doplněny o experimentální studii DMPS, která byla prezentována v literatuře. Takto byla získána řada molekul, které jsou strukturně podobné, ale mají výrazně rozdílné chování během fragmentace. Pomocí měření účinného průřezu byly měřeny disociační energie vazeb a tyto disociační energie byly vypočteny pomocí metody DFT. Kombinací teoretického výpočtu metodou DFT a experimentálního měření jsme poukázali na společné rysy a na rozdíly ve fragmentačním schématu všech tří molekul. Navrhli jsme odštěpení dvou vodíkových atomů během plazmově indukovaného fragmentačního procesu. Vodíky mohou být odštěpeny pomocí dvou mechanismů: i. odštěpení dvou vodíků jeden po druhém a ii. odštěpení molekuly H2 v jednom kroku. Z profilů energie dokážeme určit, který mechanismus bude v tom konkrétním případě pravděpodobnější. Předpokládaný mechanismus je v korelaci s experimentálními výsledky fragmentace zjištěnými z hmotnostních spekter.

Style APA, Harvard, Vancouver, ISO itp.

23

Steichen, Valentin. "Développement d’un analyseur en énergie pour la caractérisation des hautes atmosphères neutres et ionisées terrestre et planétaires". Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS635.

Pełny tekst źródła

Streszczenie:

L'étude de la dynamique des particules dans la thermosphère - ionosphère et dans l'exosphère des corps du système solaire permet d'approfondir notre compréhension de ces régions critiques qui sont l’interface entre une planète et l'espace. Le but de ma thèse était de développer, construire et tester un analyseur en énergie pour l'étude des hautes atmosphères planétaires : INEA (Ion and Neutral Energy Analyser). L'instrument vise à mesurer la structure énergétique des constituants neutres et ioniques présents dans cette région. Pour réaliser cette tâche difficile, INEA s'appuie sur deux concepts : une source d'ions innovante, basée sur l’utilisation de nanotubes de carbone comme émetteur d'électrons et un analyseur en énergie électrostatique, capable d'imager directement la distribution en énergie des particules. Au cours de ces trois années de thèse, un modèle numérique de INEA a été développé afin de répondre aux objectifs instrumentaux imposés par les mesures nécessaires à la caractérisation des hautes atmosphères. Parallèlement, j'ai travaillé au développement d'une source d'ionisation, également nécessaire au fonctionnement optimal de INEA, basée sur l'utilisation de nanotubes de carbone comme émetteurs d'électrons. Le développement du détecteur, une autre partie importante de l'instrument, a également été réalisé. Suite à la modélisation numérique et aux travaux réalisés sur les différentes parties de l'instrument, un premier prototype d’INEA a été conçu et assemblé, ce prototype étant actuellement testé. Avec le travail réalisé au cours de cette thèse, nous avons pu proposer deux instruments pour de futures missions spatiales : M-INEA sur la mission M-MATISSE proposé pour l'appel à projet M7 de l'ESA, récemment sélectionnée pour une phase A jusqu’en 2026, et PSEE, un émetteur d'électrons dédié au contrôle de PRELUDE SAT ; un CubeSat de 6U développé par deux universités japonaises devant être lancé mi-2025
Studying the dynamic of particles in the thermosphere – ionosphere and in the exosphere of bodies in the Solar System allows to deepen our understanding of these critical regions that are the bridge between a planet and space. The aim of my thesis was to develop, build and test a neutral particles energy analyser for studying the upper planetary atmospheres: INEA (Ion and Neutral Energy Analyser). The instrument aims to measure the energy structure of the neutral and ion constituents present in the upper atmosphere. To achieve this challenging task, INEA relies on two concepts: an innovative ion source that is based on a carbon nanotube array as an electron emitter and an electrostatic energy analyser which is able to image directly the energy distribution of the particles. During these three years of thesis, a numerical model of INEA was developed in order to meet the instrumental objectives imposed by the measurements needed to characterize the upper atmospheres. At the same time, I have been working on the development of an ion source, also necessary for the optimal operation of INEA, based on the use of carbon nanotubes as electron emitters. The development of the detector, another important part of the instrument has also been conducted. Following the numerical modelling and the work achieved on the different parts of the instrument, a first prototype of INEA has been designed and assembled. This prototype being currently tested. With the work achieved during this thesis, we have been able to propose two instruments for future space missions: M-INEA on the M-MATISSE mission proposed for the ESA M7 call for project, recently selected for a phase A study up to mid-2026, and PSEE, an electron emitter dedicated to the control of PRELUDE SAT, a 6U CubeSat developed by two Japanese universities scheduled to be launched mid-2025

Style APA, Harvard, Vancouver, ISO itp.

24

Launay, Kévin. "Synthèse de nouveaux espaceurs alcoxyamine pour la préparation de polymères encodés". Electronic Thesis or Diss., Aix-Marseille, 2020. http://www.theses.fr/2020AIXM0487.

Pełny tekst źródła

Streszczenie:

Le monde numérique est en croissance permanente, ce qui nécessite de plus en plus d’espace de stockage. Cependant, les données numériques sont stockées sur des supports dont la durée de vie n’excède généralement pas quelques dizaines d’années. Ainsi, certaines entreprises leaders du monde numérique comme Microsoft, ont engagé des efforts dans la production de systèmes de stockage basés sur de l’ADN. Ce polymère souffre cependant d’un désavantage majeur : sa structure est fixée par la biologie. A l’inverse, la structure de polymères synthétiques peut être choisie et ajustée en fonction des besoins de l’utilisateur en termes d’écriture et de lecture. Cette thèse s’inscrit dans un projet de stockage d’informations digitales sur des poly(phosphodiester)s qui ont démontré leur capacité à produire des chaînes de taille comparable à celle de brins d’ADN synthétiques. Ces polymères sont séquencés en spectrométrie de masse par la dissociation des liaisons phosphodiester entre les bits dans des expériences de MS/MS. Afin de faciliter le séquençage des plus longues chaînes, elles ont été segmentées par l’ajout d’espaceurs de faible énergie de dissociation : les alcoxyamines. Les sous-segments sont séparés en MS/MS puis séquencés en pseudo-MS puissance 3. La lecture ne pouvait cependant être automatisée à cause de pics parasites provenant de réactions induites par le radical carboné issu de la rupture de la liaison alcoxyamine. Deux stratégies ont été suivies pour empêcher ces réactions : diminuer la réactivité du radical et rigidifier l’espaceur. La première s’est avérée insuffisante, mais la seconde a permis une couverture complète et automatisée de la séquence en quelques millisecondes
The constant growth of the digital world requires more and more storage space. Data is however stored on devices whose life-times are counted in decades at best. Therefore, leading companies of the digital world like Microsoft have engaged efforts to produce DNA-based storage systems. This polymer however suffers from a major disadvantage: its structure is fixed by biology. Conversely, the structure of synthetic polymers can be chosen and adjusted to fit the user’s requirements in terms of writing and reading. This thesis is included in a project involving digital storage of information on poly(phosphodiester)s which proved able to produce polymer chains of size comparable to man-made DNA strands. These polymers are sequenced in mass spectrometry by dissociation of the phosphodiester bonds between the bits in MS/MS experiments. In order to facilitate their sequencing, the longest chains were separated into sub-segments through the inclusion of spacers with a low bond dissociation energy: alkoxyamines. Sub-segments were separated in MS/MS and sequenced in pseudo-MSpower3 experiments. However, the reading could not be automatized because of several undesired peaks. Indeed, the flexibility of the chain was so that the highly reactive carbon-radical issued from alkoxyamine fragmentation induced several undesired dissociation pathways leading to their emergence. Two strategies were pursued in this thesis to prevent these side reactions: reducing the radical reactivity and increasing the stiffness of the backbone structure. The first one proved insufficient but the second one allowed complete, automated millisecond sequencing

Style APA, Harvard, Vancouver, ISO itp.

25

Manea, Vladimir. "Penning-trap mass measurements of exotic rubidium and gold isotopes for a mean-field study of pairing and quadrupole correlations". Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112246/document.

Pełny tekst źródła

Streszczenie:

Les noyaux les plus complexes sont situés entre les nombres magiques et les médianes des espaces de valence, dans des régions connues pour les changements abrupts des observables nucléaires. Dans ces régions appelées de transition de forme, le paradigme nucléaire change entre la goutte liquide vibrationnelle et le rotor statique. Sauf quelques exceptions, les noyaux de ces régions sont radioactifs, avec des demi-vies qui chutent dans les millisecondes. Complémentaires aux propriétés des états excités à basse énergie, les énergies de liaison et les rayons de charge nucléaires sont parmi les observables les plus sensibles à ces changements de structure nucléaire. Dans ce travail, une étude du phénomène de transition de forme est effectuée, par des mesures de nucléides radioactifs produits dans le laboratoire ISOLDE au CERN. Les masses des isotopes de rubidium riches en neutrons 98-100Rb et des isotopes d’or riches en protons 180,185,188,190,191Au sont mesurées avec le spectromètre de masse de type Penning ISOLTRAP. La masse de 100Rb est déterminée pour la première fois. Des déviations significatives par rapport à la littérature sont trouvées pour les isotopes 188,190Au. Une nouvelle méthode expérimentale est présentée, utilisant un spectromètre de masse à multi-réflexion comme analyseur de faisceau pour la spectroscopie laser d’ionisation résonante. La nouvelle méthode donne la possibilité d’effectuer des études de structure hyperfine atomique avec ISOLTRAP, dont on peut extraire les rayons de charge et les moments électromagnétiques nucléaires
The most complex nuclei are situated between the magic and the mid-shell ones, in regions known for sudden changes of the trends of nuclear observables. These are the so-called shape-transition regions, where the nuclear paradigm changes from the vibrational liquid drop to the static rotor. With few exceptions, nuclei in these regions are radioactive, with half-lives dropping into the millisecond range.Complementing the information obtained from the low-lying excitation spectrum, nuclear binding energies and mean-square charge radii are among the observables most sensitive to these changes of nuclear structure. In the present work, a study of the shape-transition phenomenon is performed by measurements of radioactive nuclides produced by the ISOLDE facility at CERN. The masses of the neutron-rich rubidium isotopes 98−100Rb and of the neutron-deficient gold isotopes 180,185,188,190,191Au are determined using the Penning-trap mass spectrometer ISOLTRAP. The mass of 100Rb is determined for the first time. Significant deviations from the literature values are found for the isotopes 188,190Au. A new experimental method is presented, using a recently developed multi-reflection time-of-flight mass spectrometer as a beam-analysis tool for resonance-ionization laser spectroscopy. The new method opens the path to measurements of atomic hyperfine spectra with ISOLTRAP, from which charge radii and electromagnetic moments of radioactive nuclides can be extracted. The properties of the studied nuclides map the borders of two prominent regions of quadrupole deformation, which constrain the fine balance between pairing and quadrupole correlations in the nuclear ground states. This balance is studied by the Hartree-Fock- Bogoliubov (HFB) approach. The sensitivity of the shape-transition phenomenon to the strength of pairing correlations is demonstrated. In particular, the strong odd-even staggering of charge radii in the mercury isotopic chain is shown to result in the HFB approach from the fine interplay between pairing, quadrupole correlations and quasi-particle blocking

Style APA, Harvard, Vancouver, ISO itp.

26

Lemire, Sharon Warford. "Rigorous analytical applications of liquid secondary ion mass spectrometry/mass spectrometry". Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/30026.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

27

Dabney, David E. "Analysis of Synthetic Polymers by Mass Spectrometry and Tandem Mass Spectrometry". University of Akron / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=akron1259021862.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

28

Staněk, Jan. "Kvantitativní analýza matricových prvků metodami SIMS a LEIS". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-402575.

Pełny tekst źródła

Streszczenie:

This thesis studies comparison and connection of two spectrometric methods – low energy ion scattering spektrometry (LEIS) and secondary ion mass spectrometry (SIMS). SIMS method, despite its many positive qualities, suffers of so called matrix effect, which makes quantifiaction of data very difficult. LEIS method on the other hand is immune to this effect and so it’s suitable completion of SIMS method. As a convenient sample have been chosen AlGaN samples with various concentration of gallium and aluminium. In the first part of thesis is introduced physical essence of SIMS and LEIS method, experimental details and studied samples. In second part of the thesis there’s a description of measurements and comparison of data gained by each method.

Style APA, Harvard, Vancouver, ISO itp.

29

Goodwin, Lee. "Capillary electrophoresis-mass spectrometry and tandem mass spectrometry studies of ionic agrochemicals". Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398906.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

30

Shliaha, Pavel Vyacheslavovich. "Investigation of protein abundance and localization by mass spectrometry and ion-mobility spectrometry-mass spectrometry methods". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708661.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

31

Yuen, Wei Hao. "Ion imaging mass spectrometry". Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.564395.

Pełny tekst źródła

Streszczenie:

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.

Style APA, Harvard, Vancouver, ISO itp.

32

Berezovskaya, Yana. "Investigation of protein-ion interactions by mass spectrometry and ion mobility mass spectrometry". Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/7747.

Pełny tekst źródła

Streszczenie:

Protein‐ion interactions play an important role in biological systems. A considerable number of elements (estimated 25 – 30) are essential in higher life forms such as animals and humans, where they are integral part of enzymes involved in plethora of cellular processes. It is difficult to overestimate the importance of thorough understanding of how protein‐ion interplay affects living cell in order to be able to address therapeutic challenges facing humanity. Presented to the reader’s attention is a gas‐phase biophysical analysis of peptides’ and proteins’ interactions with biologically relevant ions (Zn2+ and I–). This investigation provides an insight into conformational changes of peptides and proteins triggered by ions. Mass spectrometry and ion mobility mass spectrometry are used in this work to probe peptide and protein affinities for a range of ions, along with conformational changes that take place as a result of binding. Observation of peptide and protein behaviour in the gas phase can inform the investigator about their behaviour in solution prior to ionisation and transfer from the former into the latter phase. Wherever relevant, the gas‐phase studies are complemented by molecular dynamics simulations and the results are compared to solution phase findings (spectroscopy). Two case studies of protein‐ion interactions are presented in this thesis. Firstly, sequence‐to‐structure relationships in proteins are considered via protein design approach using two synthetic peptide‐based systems. The first system is a synthetic consensus zinc finger sequence (vCP1) that is responsive to zinc: it adopts a zinc finger fold in the presence of Zn2+ by coordinating the metal ion by two cysteines and two histidines. This peptide has been selected as a reference for the zinc‐bound state and a simple model to refine the characterisation method in preparation for analysis of a more sophisticated second system – dual conformational switch. This second system (ZiCop) is designed to adopt either of the two conformations in response to a stimulus: zinc finger or coiled coil. The reversible switch between the two conformational states is controlled by the binding of zinc ion to the peptide. Interactions of both peptide systems with a number of other divalent metal cations (Co2+, Ca2+ and Cu2+) are considered also, and the differences in binding and switching behaviour are discussed. Secondly, protein‐salt interactions are investigated using three proteins (lysozyme, cytochrome c and BPTI) using variable temperature ion mobility mass spectrometry. Ion mobility measurements were carried out on these proteins with helium as the buffer gas at three different drift cell temperatures – ‘ambient’ (300 K), ‘cold’ (260 K) and ‘hot’ (360 K), and their conformational preferences in response to HI binding and temperature are discussed.

Style APA, Harvard, Vancouver, ISO itp.

33

Liu, Xiumin. "Mass Spectrometry and Tandem Mass Spectrometry Analysis of Polymers and Polymer-Protein Interactions". University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1406838246.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

34

Kaleta, Erin. "Applications of mass spectrometry to bacterial diagnostics: Affinity capture matrix assisted laser desorption/ionization mass spectrometry and polymerase chain reaction mass spectrometry". Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/305352.

Pełny tekst źródła

Streszczenie:

This dissertation presents the application of mass spectrometry to the detection and characterization of microorganisms based on biomarker identification and DNA analysis. Two major topics are covered: affinity capture mass spectrometry using immunoassay methods and methods involving insertion of membrane receptors into polymerized planar supported lipid bilayers; and the application of mass spectrometry for use in clinical microbiology for the identification of microorganisms causing bloodstream infections. Affinity capture mass spectrometry on immunoassay-based platforms studied the capture of Protein A from Staphylococcus aureus , demonstrating capture that is both selective and sensitive. Experiments illustrated successful capture from a purified source and cell lysates. Affinity capture using receptors inserted into polymerized lipid bilayers was also performed using GM1 and cholera toxin subunit B, demonstrating the enhanced stability offered by polymerizing the lipid bilayers such that direct ionization could be performed. Detection of protein binding was achieved with mass spectrometry at low molar ratios of receptor, and enzymatic digestion experiments on the protein retained at the surface illustrated the ability to characterize the protein ligand bound, lending support to using this technique for reverse pharmacological applications. Lastly, experiments demonstrated that affinity capture of surface-bound proteins can also be used to extract cells from complex mixture prior to the polymerase chain reaction, illustrating utility as a pre-treatment for detecting microorganisms in blood samples. Mass spectrometry was applied to detection of microorganisms from blood culture bottles collected from patients with bloodstream infections. Polymerase chain reaction electrospray ionization and whole cell matrix-assisted laser desorption/ionization mass spectrometry were used to characterize hematopathogens. High diagnostic accuracy was demonstrated with respect to culture-based testing and these two platforms were compared considering accuracy in identification, time to result, and cost benefit analysis. The experiments presented here cover a broad range of detection strategies for identifying proteins and microorganisms. The affinity capture techniques describe the first application of peptide capture and polymerized bilayers for mass spectrometric analysis, and the clinical mass spectrometry work demonstrates validation of two emerging techniques and the first comparative study on both platforms simultaneously. All research presented here demonstrates promise for application of mass spectrometry in diagnostic biology.

Style APA, Harvard, Vancouver, ISO itp.

35

Sun, Xiaobo. "Forensic Applications of Gas Chromatography/Mass Spectrometry, High Performance Liquid Chromatography--Mass Spectrometry and Desorption Electrospray Ionization Mass Spectrometry with Chemometric Analysis". Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1329517616.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

36

Woods, Lucy Ann. "Characterising amyloid assembly using ion mobility spectrometry-mass spectrometry". Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.590277.

Pełny tekst źródła

Streszczenie:

From small molecules to macromolecules, mass spectrometry has evolved significantly over the past decade, progressing from a tool to identify chemical elements to a powerful technique able to elucidate structural information for large protein complexes. With the interfacing of ion mobility spectrometry to mass spectrometry (IMS-MS), mass spectrometric analyses now occupy an extra dimension, providing unrivalled separation and structural characterisation of lowly-populated species in heterogeneous mixtures. One biological system that has benefitted enormously from such advances is the study of in vitro amyloid formation. The ability of amyloidogenic proteins to assemble into insoluble fibrils is associated with over twenty-five different disease states. Beta-2 microglobulin (β2m) is one such protein able to assemble into amyloid fibrils in vitro, although assembly can only be initiated upon destabilisation of the native structure. Identifying which states initiate fibril formation is challenging. as few techniques are able to separate and characterise such transient species. In addition, recent research has identified a number of small molecule inhibitors of fibrillation and understanding their mechanism of action is a topic of current interest. Here, the power of IMS-MS has been harnessed to achieve the separation and characterisation of monomeric and oligomeric precursors of amyloid fibril formation of the protein β2m. Analysis of oligomeric species populated during fibril formation, in addition to the effects of small molecule inhibitors on oligomer population, has led to the identification of oligomeric species on-pathway to fibril formation. Further investigation into fibrils of different morphologies has also been conducted using IMS and limited proteolysis, Differences in oligomeric populations have been revealed, together with differences in fibril structure. Each of these results highlights how MS can be used to give insights into the mechanism of amyloid formation and highlight the potentials of this approach for screening for potential inhibitors of any assembly reaction.

Style APA, Harvard, Vancouver, ISO itp.

37

Zhou, Yi. "Microfluidics interfacing to mass spectrometry". College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7402.

Pełny tekst źródła

Streszczenie:

Thesis (Ph. D.) -- University of Maryland, College Park, 2007.
Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Style APA, Harvard, Vancouver, ISO itp.

38

Testino, Samuel A. Jr. "Optimization strategies in mass spectrometry". Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/26972.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

39

Rostom, Adam A. "Mass spectrometry of protein interactions". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312385.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

40

Winter, David. "Drug analysis by mass spectrometry". Thesis, University of Canterbury. Chemistry, 1986. http://hdl.handle.net/10092/6560.

Pełny tekst źródła

Streszczenie:

1. The pharmacokinetics of morphine have been measured in four patients with renal failure and three healthy volunteers following intramuscular administration of papaveretum. Morphine blood levels were determined using GCMS with specific ion monitoring. The significantly shorter drug elimination half-life found for the patients suggests that renal failure does not impair the elimination of morphine. 2. A CI GCMS assay with specific ion monitoring has been developed for measuring the anti parkinsonian drug benztropine in post-mortem specimens. The assay is potentially more sensitive than a similar assay using electron impact ionisation. 3. The level of atropine in an aqueous extract of Datura stramonium has been measured by GCMS with selected ion monitoring. The results show that such an extract will contain most of the atropine present in the plant material. The levels are such that several medium sized glassfuls will contain sufficient atropine to constitute a dangerous drug dose. 4. A Hewlett-Packard 5982A GCMS has been successfully modified to allow it to be used to record in-beam mass spectra with a commercially available DCI probe. The effectiveness of these modifications is discussed and in-beam mass spectra of some physiologically active compounds are presented.

Style APA, Harvard, Vancouver, ISO itp.

41

Perkins, John Robert. "Supercritical fluid chromatography/mass spectrometry". Thesis, Cardiff University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375969.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

42

Smith, Derek John. "Femtosecond Laser Mass Spectrometry (FLMS)". Thesis, University of Glasgow, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264149.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

43

Sweet, Steve M. M. "Phosphoprotein analysis by mass spectrometry". Thesis, University of Manchester, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538385.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

44

Cobice, Diego Federico. "Mass spectrometry imaging of steroids". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/21032.

Pełny tekst źródła

Streszczenie:

Glucocorticoids are steroid hormones involved in the stress response, with a well-established role in promoting cardiovascular risk factors including obesity and diabetes. The focus of glucocorticoid research has shifted from understanding control of blood levels, to understanding the factors that control tissue steroid concentrations available for receptor activation; it is disruption of these tissue-specific factors that has emerged as underpinning pathophysiological mechanisms in cardiovascular risk, and revealed potential therapeutic targets. However, the field is hampered by the inability at present to measure concentrations of steroid within individual tissues and indeed within component cell types. This research project explores the potential for steroid measurements using mass spectrometry-based tissue imaging techniques combining matrix assisted laser desorption ionization with on-tissue derivatisation with Girard T and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (OTCD-MALDIFTICRMS). A mass spectrometry imaging (MSI) platform was developed and validated to quantify inert substrate and active product (11-dehydrocorticosterone (11DHC), corticosterone (CORT) respectively) of the glucocorticoid-amplifying enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in rodent tissues. A novel approach to derivatising keto-steroids in tissue sections using Girard T reagent was developed and validated. Signals were boosted (10⁴ fold) by formation of GirT hydrazones compared to non-derivatised neutral steroids. Active and inert glucocorticoids were detected in a variety of tissues, including adrenal gland and brain; in the latter, highest abundance was found in the cortex and hippocampus. The MSI platform was also applied to human biopsies and murine tissues for the analysis of other ketosterols such as androgens and oxysterols. Proof-of-principle validation that the MSI platform could be used to quantify differences in enzyme activity was carried out by following in vivo manipulation of 11β-HSD1. Regional steroid distribution of both substrate and product were imaged at 150-200μm resolution in mouse brain sections, and the identification confirmed by collision induced dissociation/liquid extraction surface analysis (CID-LESA). To validate the technique, the CORT/11DHC ratios (active/inert) were determined in 11β- HSD1 deficient mice and found to be reduced (KO vs WT; cortex (49 %*); hippocampus (46 %*); amygdala (57 %)). Following pharmacological inhibition by administration of UE2316, drug levels peaked at 1 h in tissue and at this time point, a reduction in CORT/11DHC ratios were also determined, although to a lesser degree than in KO mice, cortex (22%), hippocampus (25 %) and amygdala (33 %). The changes in ratios appeared driven by accumulation of DHC, the enzyme substrate. In brains of mice with 11β-HSD1 deficiency or inhibition, decreases in sub-regional CORT/11DHC ratio were quantified, as well as accumulation of an alternative 11β- HSD1 substrate, 7-ketocholesterol. MSI data correlated well with the standard liquid chromatography tandem mass spectrometry (LC-MS/MS) in whole brain homogenates. Subsequently, the MSI platform was also applied to measure the dynamic turnover of glucocorticoids by 11β-HSD1 in metabolic tissues using stable isotope tracers (Cortisol-D4 (9,11,12,12-D4) (D4F). D4F was detected in plasma, liver and brain after 6 h infusion and after 48 h in adipose. D3F generation was detected at 6 h in plasma and liver; at 24 h in brain specifically in cortex, hippocampus and amygdala; and at 48 h in adipose. The spatial distribution of d3F generation in brain by MSI closely matched enzyme localisation. In liver, an 11β-HSD1-riched tissue, substantial generation of d3F was detected, with a difference in d4F/d3F ratios compared with plasma (ᴧTTRᴧ 0.18± 0.03 (6 h), 0.27± 0.05 (24 h) and 0.38±0.04 (48 h)). A smaller difference in TTR was also detected between plasma and brain (ᴧTTR 0.09 ± 0.03 (24 h), 0.13±0.04 (48 h)), with no detectable regeneration in adipose. After genetic disruption of 11β-HSD1, d3F generation was not detected in plasma or any tissues, suggesting that 11β-HSD1 is the only enzyme carrying out this reaction. After pharmacological inhibition, a similar pattern was seen. The circulating concentration of drug peaked at 2 h and declined towards 4 h, with same pattern in liver and brain. The ᴧTTR ratios 2HPD between plasma and liver (0.27±0.08vs. 0.45± 0.04) and brain (0.11±0.2 vs. 0.19± 0.04) were smaller following drug administration than vehicle, indicating less d3F generation. Extent of enzyme inhibition in liver responded quickly to the declining drug, with ᴧTTR returning to normal by 4 h (0.38± 0.06). ᴧTTR had not normalised 4HPD in brain (0.12±0.02, suggesting buffering of this pool. In adipose, UE2316 was not detected and nor were rates of d3F altered by the drug. Two possible phase I CYP450 metabolites were identified in the brain differing in spatial distribution. In conclusion, MSI with on-tissue derivatisation is a powerful new tool to study the regional variation in abundance of steroids within tissues. We have demonstrated that keto-steroids can be studied by MALDI-MSI by using the chemical derivatisation method developed here and exemplified its utility for measuring pharmacodynamic effects of small molecule inhibitors of 11β-HSD1. This approach offers the prospect of many novel insights into tissue-specific steroid and sterol biology.

Style APA, Harvard, Vancouver, ISO itp.

45

Salter, Tara La Roche. "Metrology for ambient mass spectrometry". Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/28748/.

Pełny tekst źródła

Streszczenie:

Ambient mass spectrometry (AMS) is a new and versatile method for analysing a multitude of different sample types with the benefit of analysis at ambient pressure and the many other advantages that this entails. However, as these techniques are still in their infancy, metrological development of the techniques is essential. This is a critical step before AMS can be used reliably in the application areas in which it has shown great promise. The research in this thesis addresses the development of AMS sources, in particular plasma-assisted desorption-ionisation, PADI. Optimisation and characterisation is fundamental to understanding and developing the technique. Optimisation of PADI is addressed; this includes understanding the effects of different parameters to maximise signal intensities. The power, and temperature, of the plasma is shown to have a significant effect on the fragmentation observed in the mass spectra. This is an important result that is further explored with the use of thermal desorption to aid the analysis of low volatility molecules. The form of the analyte is also an important consideration for analysis by PADI; characteristic ions from powders are easily detected, whereas for thin film samples an analyte vapour pressure of greater than 10-4 Pa is needed. This result provides an indication of the limitations of PADI and what classes of analyte it will be successful at analysing. It is also shown that we can improve signal intensities using a heated sample stage allowing the analytes to be thermally desorbed before being ionised by the plasma. This is an important result for future work, where ambient plasma sources can be implemented as an ionisation source in conjunction with another mechanism, such as thermal or laser desorption, to generate gas-phase ions. A comparison of different ambient methods for personal care products shows the usefulness and also complementarities of PADI with desorption electrospray ionisation, DESI, one of the most established AMS techniques which utilises a different mechanism for desorption and ionisation. This also demonstrates the chemical information that can quickly be gained from these techniques, with minimal sample preparation. DESI is also compared to secondary ion mass spectrometry, SIMS. Vacuum-based techniques such as SIMS are much more established than ambient techniques; it is insightful to understand the advantages that each source can offer, for the analysis of different types of molecule as well as the mass spectral information that can be gained from SIMS and DESI.

Style APA, Harvard, Vancouver, ISO itp.

46

McClure, Thomas Dale. "Biomedical applications of mass spectrometry". Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185490.

Pełny tekst źródła

Streszczenie:

The application of mass spectrometry to verification of the structure of 3-methyluridine (m³U) isolated by HPLC from normal human urine is described. m³U has been used as an internal standard for studies of urinary nucleosides, a practice that is discouraged with the confirmation of m³U as a naturally occurring compound. Mass spectrometry has been used for the identification of 5'-deoxyxanthosine (5'-dX) a novel nucleoside in normal human urine. Initial concern over availability of a reference sample of 5'-dX prompted investigations of the structure/fragmentation relationships of the TMS deratives of 2'-, 3'-, and 5'-deoxynucleosides toward differentiation between the three deoxynucleosides. Results are presented which allow discrimination between the model compounds, deoxyanalogs of adenosine. Subsequent to the deoxynucleoside fragmentation studies, a biosynthetically produced reference sample of 5'-dX became available for direct comparison of mass spectra and chromatographic retention times which, when combined with observations from the deoxynucleoside studies established the structure of 5'-dX. In response to the large number of mass spectra produced from the GC-MS analysis of a TMS derivatized urine sample, computer software has been written to aid in spectral analysis. Examples are shown in which the software uses established fragmentation rules to assign structure to ions in the mass spectrum and suggest modifications in the sugar portion of two urinary nucleosides. The structure/fragmentation relationships of the unique antitumor drug taxol has been studied by EI, CI and FAB mass spectrometry. Information is presented showing characteristic fragmentation of the side-chain and verification of functional groups attached to the taxane ring. Studies have been conducted to determine the relationship between target temperature and matrix and sample lifetime in the source of the mass spectrometer. Results are presented showing that cooling the target permits the use of matrix materials that are too volatile at ambient temperatures thus extending the range of compounds that can be studied by mass spectrometry. A recently constructed four-sector mass spectrometer is described with a detailed discussion of instrumental capabilities. Results of experiments designed to apply these capabilities to the structural analysis of TMS nucleosides using FAB ionization are discussed with an emphasis on the fragmentation unique to 4-sector daughter ion experiments compared with conventional studies and 2-sector daughter ion results.

Style APA, Harvard, Vancouver, ISO itp.

47

Offei, Felix. "Denoising Tandem Mass Spectrometry Data". Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/etd/3218.

Pełny tekst źródła

Streszczenie:

Protein identification using tandem mass spectrometry (MS/MS) has proven to be an effective way to identify proteins in a biological sample. An observed spectrum is constructed from the data produced by the tandem mass spectrometer. A protein can be identified if the observed spectrum aligns with the theoretical spectrum. However, data generated by the tandem mass spectrometer are affected by errors thus making protein identification challenging in the field of proteomics. Some of these errors include wrong calibration of the instrument, instrument distortion and noise. In this thesis, we present a pre-processing method, which focuses on the removal of noisy data with the hope of aiding in better identification of proteins. We employ the method of binning to reduce the number of noise peaks in the data without sacrificing the alignment of the observed spectrum with the theoretical spectrum. In some cases, the alignment of the two spectra improved.

Style APA, Harvard, Vancouver, ISO itp.

48

SPEZZANO, ROBERTO. "Lipids and Mass Spectrometry Application". Doctoral thesis, Università degli Studi di Milano, 2019. http://hdl.handle.net/2434/647470.

Pełny tekst źródła

Streszczenie:

During my PhD courses I focused attention on the applications of mass spectrometry in lipidomic studies. I applied mass spectrometry in several experimental models to try to observe differences in selected metabolites affected by a particular pathology. The first project performed in experimental model of impaird lipogenesis highlighted a cross talk between altered fatty acid synthesis and neuroactive steroid levels. The second project, mass spectrometry application allows to understand he effect of short-term diabetes on cholesterol metabolism. In the last project lipidomic pattern was investigated in experimental model of SCA38. Results obtained highlighted as elovl5 mutation affect phospholipids profile.

Style APA, Harvard, Vancouver, ISO itp.

49

Mohan, Krishnan R. "Fast atom bombardment mass spectrometry and tandem mass spectrometry : conditions for measurement of reproducible spectra". Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/27159.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

50

Catron, Brittany Lyn. "Analysis of Protein:RNA Cross-links by Inductively Coupled Plasma Mass Spectrometry and Tandem Mass Spectrometry". University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1337885809.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

Rozprawy doktorskie na temat „Mass and Energy spectrometry”

Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych