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1
Wronska, Louisa Victoria May. « The factors & ; protocols that influence accuracy, precision & ; uncertainty of accurate mass measurements by Fourier transform ion cyclotron resonance mass spectrometry to validate the assignment of elemental composition ». Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/67059/.
Texte intégralRésumé :
The need for very accurate mass measurements of compounds is becoming more demanding with the expansion of the number of compounds in need of correct identification and with the limits of elemental analysis; a fast, robust analytical solution is sought. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) is a very powerful tool for undertaking accurate mass measurements because of its high resolving power and mass accuracy. The use of FT-ICR MS in a high-throughput environment is limited due to the need of operator intervention required to obtain optimum accurate mass measurements. The lowest mass measurement errors (MME) are usually obtained using internal calibration, as the sample and calibrant ions inside the ICR cell experience the same conditions. However, internal calibration requires calibrant ions to be selected according to the mass of the sample ion, which requires operator intervention. External calibration is the preferred choice when performing accurate mass measurements in a high-throughput environment, as a calibration can be acquired independently of the sample. This study aims to demonstrate the use of ion population balancing using a dual sprayer approach to reduce MME. Population balancing between sample ions and calibrant ions can reduce the MME 40-fold. Ion populations across a chromatographic run can also vary greatly. The dual sprayer can also be employed to easily control the ion populations of both sample and calibrant entering the cell and can help to reduce ion suppression. The aim of the latter part of the work was to address the uncertainty of an accurate mass measurement performed using FT-ICR MS. In order to confidently select an elemental formula following an accurate mass measurement, a ‘cut-off’ limit or tolerance has to be selected. This tolerance can be set by calculating the uncertainty of the measurement; without an uncertainty component the measurement is meaningless. The work herein demonstrates how to calculate uncertainty of an accurate mass measurement with the aim that journals will adopt a procedure of only accepting an accurate mass measurement which quotes an uncertainty.
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Martin, Riana Theresa. « Evaluation of capillary electrophoresis as an analytical technique using bulk ionic composition of fluid inclusions in quartz ». Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51751.
Texte intégralRésumé :
Thesis (MSc)--Stellenbosch University, 2000.ENGLISH ABSTRACT: This study was initialized to introduce capillary electrophoresis (CE) as a useful technique in the analysis of fluid inclusions in quartz. lts advantages are low detection limits for the dissolved ionic content of the fluid, the small amount of sample (1 g or less) for a detailed qualitative and quantitative analysis, and the short time required to obtain results (one run for either cations or anions take approximately 10 minutes). The study area from which quartz veins were selected is situated within the Neoproterozoic Saldania belt. Syn- and post-tectonic S-, 1- and A-type granitoids from the Cape Granite Suite intruded the metamorphosed Malmesbury greywacke and pelites between 550 and 510 Ma. Additional periods of tectonism and metamorphism occurred during Cape Supergroup sedimentation (480 - 400 Ma) as well as Karoo sedimentation and the simultaneous Cape Orogeny (280 -215 Ma). The quartz-biotite±chlorite vems are hosted by Cape Granite as well as Malmesbury sediments. These barren quartz veins are part of two vein sets, one dipping at an angle between 15 and 500 to the S to SE and striking W, similar to Sn-mineralized quartz veins in the SW-cape, while the other is near-vertical and striking W to NW. Except for their orientation, no differences regarding associated minerals, inclusion characteristics or fluid chemistry indicated a difference in origin. Four fluid phases within a temperature range of 160 - 390 °C were identified as being largely late-magmatic and released from the underlying Cape Granite plutons, namely an early 370- 390 °C population, followed by the 310 - 360, 230 - 300 and lastly the 160 - 200 °C populations. Initiation of this fluid system occurred from at least SlOMa, after final granite intrusion, but the age of the final stage is unknown. Renewed fluid circulation occurred during a later period of metamorphism, possibly during the Cape Orogeny. These fluids had temperatures between 240 and 360°C and are of sedimentary origin, most likely released from the Malmesbury metamorphites. The technique of capillary electrophoresis has been evaluated for its application to bulk fluid inclusion analysis, and the crush-leach fluid extraction procedure of Bottrell, et al., (1988) optimized for CE analysis. Contamination factors were identified and minimized or eliminated, where possible. Bulk fluid inclusion chemistry obtained by CE was therefore proved to provide valuable information regarding the various fluid generations as long as inclusion populations are investigated individually to explain and correlate bulk data.
AFRIKAANSE OPSOMMING: Die doel van die studie was om te toon dat die tegniek van kapillêre elektroforese bruikbaar is in die analiese van vloeistofmsluitsels in kwarts. Die voordele van hierdie tegniek is lae deteksie limiete vir die opgeloste ioon inhoud van die vloeistof, die klein monstergrootte (< 1g) wat nodig is vir 'n omvattende kwalitatiewe en kwantitatiewe analise, en die kort tydsduur waarin resultate verkry word ('n katioon of anioon analise vir een monster duur lO minute). Die studie gebied waar kwarts are gemonster is, is binne die Neoproterosoïese Saldania Gordel geleë. Sin- en laat-tektoniese S-, I- en A-tipe graniete van die Kaapse Graniet Suite het die gemetamorfiseerde Malmesbury grouwakke en peliete tussen 550 en 510 Ma binnegedring. Latere periodes van tektonisme en metamorfose het tydens deponering van die Kaap Supergroep (480 - 400 Ma), en die gelyktydige episodes van Karoo sedimentasie en Kaapse Orogenese (280 - 215 Ma) plaasgevind. Die gasheer gesteentes vir die kwarts-biotiet±chloriet are is Kaapse Graniet sowel as Malmesbury sedimente. Hierdie ongemineraliseerde are is deel van twee aarstelsels, nl. een met 'n duik hoek tussen 15 en 50° S tot SO en 'n westelike strekking, soortgelyk aan die Sn- ,.gemineraliseerde are in die SW-Kaap, terwyl die ander stel are feitlik vertikaal is en W tot NW strek. Behalwe vir die verskil in oriëntasie was daar geen aanduiding, wat betref 'n verskil in geassosieerde minerale, vloeistofinsluitsel kenmerke of vloeistof chemie, dat hierdie twee aarstelsels van verskillende oorsprong is nie. Vier vloeistof fases binne 'n temperatuur gebied van 160 - 390 °C en 'n vloeistof saliniteit van 0 - 5.7 gewig % NaC1 ekw. is geïdentifiseer, met 'n laat-magmatiese assosiasie en vrygestel deur die onderliggende Kaapse Graniete. Dit behels 'n vroeë 370 - 390 °C populasie, gevolg deur die 310 - 360, 230 - 300 en laastens die 160 - 200 °C populasies. Inisiasie van hierdie sisteem kon moontlik rondom 510 Ma gelede plaasgevind het, maar die ouderdom van die finale fase is onbekend. Hernude vloeistof sirkulasie het tydens 'n later stadium van metamorfose onstaan, moontlik tydens die Kaapse Orogenese. Hierdie vloeistowwe het temperature tussen 240 en 360 °C en is van sedimentêre oorsprong waar dit moontlik deur metamorfose van die reeds gemetamorfiseerde Malmesbury gesteentes vrygestel is. Die tegniek van kapillêre elektroforese is vir die toepassing daarvan in die analise van vloeistof insluitsels in kwarts geëvalueer, terwyl die vloeistof vrystellingsmetode van Bottrell en Yardley (1988) vir hierdie tegniek geoptimaliseer is. Kontaminasie faktore is geïdentifiseer en verminder of uitgeskakel waar moontlik. Daar is getoon dat die vloeistof chemie, wat verteenwoordigend is van al die insluitsel populasies in 'n monster, wel bruikbaar is t.o.v. afsonderlike vloeistof generasies, solank elke populasie individueel bestudeer is om die omvattende chemiese data te verduidelik en met 'n enkele populasie te korrelleer.
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Toida, Mieko, Hiroyuki Higashino et Yukiharu Ohsawa. « Effect of ion composition on ion acceleration by magnetosonic shock waves ». American Institite of Physics, 2008. http://hdl.handle.net/2237/12029.
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Isildak, Ibrahim. « Ion selective electrodes in ion chromatography ». Thesis, University of Newcastle Upon Tyne, 1992. http://hdl.handle.net/10443/859.
Texte intégralRésumé :
The number of applications of potentiometric detection In Ion chromatography Is Increasing In the use of ion selective electrodes for which the response Is not limited to a few number of Ions. In this research, membrane electrodes, for a number of Ions, based on PVC were prepared to examine selectivity, detection limit and reproducibility for chromatographic and flow-injection measurements via mixed solution method and flow-injection technique. The selectivity sequence of anion selective electrodes for single charged Inorganic anions was F< Cl < Br < NO 2< NO 3
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Bissonnette, Martine C. « Ion/radical and ion/molecule complexes and ion structure assignments in the gas phase ». Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7731.
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The fragmentation mechanism of ionized neopentanol, (CH$\sb3$)$\sb3$CCH$\sb2$OH$\sp{+-}$, has been studied in great detail along with other C$\sb5$H$\sb $H$\sp{+-}$ isomers. The use of $\sp $C and D labelling was found an essential tool to establish the relation between the other species involved in the dissociation of neopentanol. The involvement of (CH$\sb3$)$\sb2$C$\sp{\cdot}$CH$\sb2\sp+$(O)HCH$\sb3$, (CH$\sb3$)$\sb3$C$\sp+$(O)HCH$\sb2$ and (CH$\sb3$)$\sb2$($\sp\cdot$CH$\sb2$)CCH$\sb2\sp+$OH$\sb2$ was essential to explain the H/D label exchange occurring upon fragmentation of neopentyl alcohol. An ion-dipole complex between methanol and ionized methyl propene is proposed as the final intermediate which leads directly to the products, methanol and ionized methyl propene. The results of the investigation of C$\sb7$H$\sb5\sp+$ ions from various precursor molecules are also described. The following compounds, which all produce C$\sb7$H$\sb5\sp+$ ions, were studied: benzyl acetate, benzyl formate, benzyl alcohol, 2-bromocyclopropabenzene, 1,6-heptadiyne and 1,5-decadiyne. According to the metastable ion (MI) mass spectra and the He collision induced dissociation (CID) of m/z 89 ions, it is suggested that four structures exist. (Abstract shortened by UMI.)
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Marto, Jarrod A. « External Ion Injection and Applications of Ion Axialization in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry / ». The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487868114113087.
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Diédhiou, Malick. « Ion Chemistry of Hydrogenated PAHs ». Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40452.
Texte intégralRésumé :
Polycyclic aromatic hydrocarbons (PAHs) are a class of organic molecules suggested to constitute roughly 20% of carbon in the interstellar medium (ISM). These species exist in both neutral and ionic forms and both are potentially involved in processes such as H2 formation. Catalyzing H2 formation necessarily involves the participation of hydrogenated PAHs as reaction intermediates. Employing tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy and theory, we have explored the unimolecular reactions of five ionized hydrogenated PAHs that vary in degree and position of hydrogenation: tetralin (1,2,3,4-tetrahydronaphthalene), 9,10-dihydroanthracene (DHA+•), 1,2,3,4-tetra- and 1,2,3,4,9,10-hexa-hydrophenanthrene (THP+• and HHP+•) and 1,2,3,4,5,6,7,8-octahydroanthracene (OHA+•). The major reactions observed were the losses of the hydrocarbons CH3•, C2H4 and C3H5• together with H• atom loss. RRKM modeling of the iPEPICO data suggested that the unimolecular chemistries were based around a two-well potential energy surface in each case. Ionized tetralin can lose all four neutrals via H-shift and ring-opening reactions, or CH3• and C2H4 after interconversion to the 1-methylindane ion, a process similar to that found for ionized 1,2-dihydronaphthalene (isomerizing to form the 1-methylindene ion structure). DHA+• exhibits the same reactions previously observed for 1,2-dihydronaphthalene and 9,10-dihydrophenanthrene, namely competing loss of H• and CH3•. However, the energy required for H•-loss, as predicted by RRKM modeling of the iPEPICO results, was lower than the latter ions, presumably due to an expansion of the electron delocalization across the central ring upon dehydrogenation. OHA+• behaves similarly to ionized tetralin, displaying losses of H•, CH3•, C2H4 and C3H5• in its collision induced dissociation (CID) mass spectra, but under iPEPICO conditions CH3•-loss is not observed. THP+•
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and HHP+• have aspects of both DHA+• and OHA+• chemistries, displaying losses of H•, CH3•, C2H4 and C3H5•. Minimum energies for all observed reaction channels were thus obtained, together with selected mechanisms computationally explored at the B3-LYP/6-31+G(d,p) level of theory. The trend in reactivity in going from tetralin and DHA+• to THP+•, HHP+• and ultimately OHA+• sees decreasing abundance of H• and CH3•-loss and an increasing dominance of the formation of C2H4, C3H5• and higher hydrocarbons with degree of hydrogenation as isomerization to a methyl-substituted ion becomes less significant. As this isomerization decreases in significance, the ions become sources of small hydrocarbon molecules and not hydrogen atoms or molecules.
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Hall, Adrian Mark. « Composition and morphology of substorm-associated ion injections ». Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30662.
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This thesis describes an investigation into the composition and morphology of substorm ion injections at magnetic latitudes and L-shells away from geostationary orbit. Furthermore, the work investigates the Dst-dependent conditions that affect these compositional and spatial characteristics. Count rate and composition measurements in the energy range 80 - 400 keV/q form the basis of the analysis. Near-equatorial observations by the CRRES spacecraft during 1991 have been used to study substorm and near-Earth magnetosphere composition, injection event distribution, and the injection region morphology. Measurements made by the Polar satellite during 1996 extend the study to high magnetic latitudes (50 - 60 °) and high L-shells (7 ≤ L ≤ 22), and are used to investigate the radial morphology of the injection region. For the first time, substorm injection rate as a function of composition, Dst, and injection type has been quantified. In storm time the rate more than doubles. This appears to result from the observed increase in the azimuthal extent of the average injection region. Analysis has shown however, that substorm onset and type (single or multiple injection events) are (for the most part) not significantly composition dependent. The threefold increase in ionospheric-rich event frequency during storm time is principally a result of the increase seen in the equatorial, dusk flank event occurrence. Ion injections have been observed over a large radial extent. Furthermore, ions drift coherently over a large range of L-shells, spanning, at times, from geostationary orbit to L ≈ 18. The inward transport of these ions is not composition dependent. The injected plasma depends on the magnetospheric composition tailward of the spacecraft. This is highly spatially variable and dependent on the past, and prevailing Dst conditions with large (fourfold) enhancements in ionospheric origin material observed inside of L ≈ 7 ( i.e. below the altitude of most substorm onsets) during storm time. The storm time nightside ring current is observed to expand both earthward and tail ward. Out of the equatorial plane, the injection rate is hypothesised to artificially decrease as a result of the tapered, crescent shaped form of the injection region.
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Pollum, Laura L. « Digital ion trap mass spectrometry for cold ion-molecule chemistry ». Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:18c6451d-d247-4384-9257-f8864e038343.
Texte intégralRésumé :
A promising new approach for studying cold ion-molecule chemical reactions is the combination of laser- or sympathetically-cooled trapped ions and slow-moving molecules from a cold molecule source, such as a quadrupole velocity selector or a Stark decelerator. Previous reaction studies using trapped atomic ions and slow molecules from a quadrupole velocity selector were able to reach average collision energies as low as 1 K. However, the guided molecules had an approximately room temperature rotational energy distribution, so the reactions studied were not truly cold. Thus, a new molecular source for producing translationally and rotationally cold molecules utilizing buffer gas cooling and quadrupole velocity selection was constructed by K. Twyman and characterized for use in cold reaction studies. This new source of cold molecules is referred to as the buffer gas guide. A new ion trap has been designed and built for use with the existing buffer gas guide. The new ion trap apparatus is compact and mechanically compatible with this new guide. It uses a linear Paul ion trap with cylindrical electrodes to trap ions. Two optical axes (one axial and one radial) enable efficient cooling of small ion crystals. A field-free time-of-flight tube and ion detection assembly are also incorporated into the apparatus. A new technique for determining the mass and quantity of trapped ions has also been developed, termed digital ion trap mass spectrometry. The new technique uses a digital RF waveform to trap ions before ejecting the ions radially from the trap using an ejection pulse applied to the trap electrodes. The ions are then detected after free flight along a time-of-flight tube. This technique was characterized by ejecting crystals of various sizes and compositions: Ca+ only, Ca+/CaF +, Ca+/CaOH +/CaOD+, and Ca+/NH +3 /NH +4 /H3O+. A linear relationship between the number of ions ejected (determined by comparing experimental and simulated crystal images) and the integral of the time-of-flight peak was observed for Ca+ and Ca+/CaF +. All mass peaks were resolved. Simulations of the trapped ions and their trajectories through the time-of-flight tube were also performed, and excellent agreement between the simulated and experimental mass resolution was observed. Progress towards combining the buffer gas guide with the previously independent ion trap is also presented. It is anticipated that the combined buffer gas guide ion trap apparatus will enable the study of ion-molecule reactions at low temperatures with translationally and rotationally cold molecules. It is anticipated that the new digital ion trap mass spectrometry technique will simplify the study of reactions when multiple product ions whose masses are separated by only 1 AMU are formed. A new ion trap has been designed and built for use with the existing buffer gas guide. The new ion trap apparatus is compact and mechanically compatible with this new guide. It uses a linear Paul ion trap with cylindrical electrodes to trap ions. Two optical axes (one axial and one radial) enable efficient cooling of small ion crystals. A field-free time-of-flight tube and ion detection assembly are also incorporated into the apparatus. A new technique for determining the mass and quantity of trapped ions has also been developed, termed digital ion trap mass spectrometry. The new technique uses a digital RF waveform to trap ions before ejecting the ions radially from the trap using an ejection pulse applied to the trap electrodes. The ions are then detected after free flight along a time-of-flight tube. This technique was characterized by ejecting crystals of various sizes and compositions: Ca+ only, Ca+/CaF+, Ca+/CaOH+/CaOD+, and Ca+/NH+3/NH+4/H3O+. A linear relationship between the number of ions ejected (determined by comparing experimental and simulated crystal images) and the integral of the time-of-flight peak was observed for Ca+ and Ca+/CaF+. All mass peaks were resolved. Simulations of the trapped ions and their trajectories through the time-of-flight tube were also performed, and excellent agreement between the simulated and experimental mass resolution was observed. Progress towards combining the buffer gas guide with the previously independent ion trap is also presented. It is anticipated that the combined buffer gas guide ion trap apparatus will enable the study of ion-molecule reactions at low temperatures with translationally and rotationally cold molecules. It is anticipated that the new digital ion trap mass spectrometry technique will simplify the study of reactions when multiple product ions whose masses are separated by only 1 AMU are formed.
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Murrell, Jason. « Some studies in ion/molecule reactions on ion trapping instruments ». Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319223.
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Pearson, C. H. G. « New ion exchange resins for ion chromatography applied to anions ». Thesis, University of Kent, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372771.
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Maxwell, Virginia Margaret. « Ion-selective electrodes ». Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329972.
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Ross, Charles William. « Gas phase ion - molecule reactions studied by Fourier transform ion cyclotron resonance mass spectrometry / ». The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487846885778077.
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Yin, Winnie Weixin. « Fourier transform ion cyclotron resonance mass spectrometric study of gas-phase ion-molecule reactions / ». The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487847309051562.
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Gill, Matthew Clive. « The ion conveyor : an ion focussing and conveying device for mass spectrometry ». Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3715/.
Texte intégralRésumé :
The advent of electrospray ionisation (ESI) has been a major factor driving the revolution which has taken place in the field of biological mass spectrometry over the past twenty years. In this thesis, efforts to improve electrospray ionisation in two respects are detailed. One is the transmission of ions from ambient pressure into the high vacuum of a mass spectrometer. The other is control and influence over making and breaking of bonds, in particular long and weak bonds, during this journey into the mass spectrometer. These improvements to electrospray ionisation have been sought through the development, theoretical analysis and application of the ion conveyor, which is an electrodynamic ion-transport device. The ion conveyor as reported here is a device consisting of stacked ring-electrodes intended for operation within the first and second differential-pumping regions of a mass spectrometer with an electrospray ionisation source. It is demonstrated how the ion conveyor achieves aspects of ion trapping and ion transport through the application of one or more radiofrequency waves to the stacked ring-electrodes. The operating principles of the device are detailed, and related technologies are described. Theoretical simulations have been used to explore for explanations for the behaviour of the device and to make predictions as to the optimum performance of the device. The first experiments with an ion conveyor and subsequent experiments with two evolved designs are described. The operation of the device has been investigated with three different types of mass spectrometer, each with its own design of electrospray ionisation source. These designs are described in detail, and the responses of the ion conveyor to various operating parameters have been characterised. A major finding was that the transmission of the ion conveyor remains significantly high in the absence of all applied potentials. This discovery reveals and emphasises the importance of mechanical forces to ion transport through the ion conveyor. A wide variety of analytes have been used in experiments to characterise the device. The mass spectra of vancomycin hydrochloride presented are of particular note, because they exhibit unusually intense peaks corresponding to the doubly charged dimer-species. The dimer of vancomycin plays the central role in long-standing theories of anti-bacterial action, but has not been observed in previous studies of vancomycin by mass spectrometry. The experimental results support the view that the ion conveyor is a useful technique for the effective transport of ions through the differential-pumping stages of an electrospray ionisation source. The results suggests that the device could be developed through appropriate manipulation of ion-neutral collisions in the higher-pressure regions to preserve and transmit delicate non-covalently bound species and facilitate their accurate measurement by means of mass spectrometry.
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Wang, Mingda. « New and improved ion traps for high resolution Fourier transform ion cyclotron resonance mass spectrometry / ». The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487681788254101.
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Chen, Ruidan. « Theory and practice of ion trap design in fourier transform ion cyclotron resonance mass spectrometry / ». The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487847309053468.
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Hannon, Michael John. « Metal ion control in oligopyridine coordination chemistry ». Thesis, University of Cambridge, 1993. https://www.repository.cam.ac.uk/handle/1810/272558.
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McKillop, Andrew G. « Ion mobilities in capillary electrophoresis ». Thesis, Loughborough University, 1996. https://dspace.lboro.ac.uk/2134/28235.
Texte intégralRésumé :
The project has investigated the electrophoretic mobilities of sets of model compounds to determine the effects of size and shape on ion mobilities. Methods were developed for the analysis of compounds in order to quote accurate electrophoretic mobilities. Using the obtained electrophoretic mobilities mobility orders were correlated with structural properties.
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Ruiz-Diaz, J. E. « Fast ion transport in solids ». Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355773.
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Bates, Paul Stephen. « Enantiomer discrimination and ion receptors ». Thesis, Durham University, 1993. http://etheses.dur.ac.uk/5689/.
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Highly lipophilic α-, β- and γ- cyclodextrin derivatives were prepared in order to obtain enantiomer selective ionophores for β-aryl ammonium ions and selective ionophores for tetrahedral ammonium ions. The extent of cyclodextrin functionalisation and the homogeneity of the products was investigated by chemical depolymerisation, (^1)H and (^13)C NMR and (+)-FAB-, FD- and ES- mass spectral analysis. For each cyclodextrin, the products of alkylation were found to consist of several constitutional isomers and homologues. These highly lipophilic molecules were incorporated into solvent polymeric membranes and investigated as electrochemical sensors for chiral molecules incorporating an aryl ring. Electrodes using BBPA as the plasticizer were stable and well defined with a limit of detection for ephedrine of -log[c] = 6.5. Interference from serum levels of Na+, K+, Ca2+ and Mg2+ is minimal (-logK(^POT) = 3.9). The electrodes were highly enantioselective in binding ephedrine and closely related homologues. The mechanism of enantiomer discrimination was investigated by several multi-nuclear NMR techniques and the complexation process was investigated by ES-MS. Lipophilic per-O-octylated α-, β- and γ- cyclodextrins exhibit size selectivity and cation discrimination in the binding of +NH4, +NMe4 and +NEt4. Sensors based on per-O-octyl-β-cyclodextrin show excellent sensitivity and good selectivity for +NMe4 over metal cations and may be used for the detection of cationic surfactants. Complexation was studied in situ and competitively by ES-MS as well as by and relaxation time acquisition. The possibility of developing several chiral crown ether and cyclam based ionophores was also investigated.
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Ichsan, E. A. W. « Ion exchange on chelating fibres ». Thesis, University of Salford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353980.
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Xu, Chao. « All silicon lithium-ion batteries ». Licentiate thesis, Uppsala universitet, Strukturkemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-261626.
Texte intégralRésumé :
Lithium-ion batteries have been widely used as power supplies for portable electronic devices due to their higher gravimetric and volumetric energy densities compared to other electrochemical energy storage technologies, such as lead-acid, Ni-Cd and Ni-MH batteries. Developing a novel battery chemistry, ‘‘all silicon lithium-ion batteries’’, using lithium iron silicate as the cathode and silicon as the anode, is the primary aim of this Ph.D project. This licentiate thesis is focused on improving the performance of the silicon anode via optimization of electrolyte composition and electrode formulation. Fluoroethylene carbonate (FEC) was investigated as an electrolyte additive for silicon composite electrodes, and both the capacity retention as well as coulombic efficiency were significantly improved by introducing 10 wt% FEC into the LP40 electrolyte. This is due to the formation of a stable SEI, which mainly consisted of FEC decomposition products of LiF, -CHFOCO2-, etc. The chemical composition of the SEI was identified by synchrotron radiation based photoelectron spectroscopy. This conformal SEI prevented formation of large amounts of cracks and continues electrolyte decomposition on the silicon electrode. An alternative lithium salt, lithium 4,5-dicyano-2-trifluoromethanoimidazole (LiTDI), was studied with the silicon electrode in this thesis. The SEI formation led to a rather low 1st cycle coulombic efficiency of 44.4%, and the SEI layer was found to contain hydrocarbon, ether-type and carbonate-type species. Different to conventional composite silicon electrodes, which require heavy and expensive copper current collector, a flexible silicon electrode, consisted of only silicon nanopowder, Cladophora nanocellulose and carbon nanotube, was facilely prepared via vacuum filtration. The electrode showed good mechanical, long-term cycling as well as rate capability performance.
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Shi, Yu. « Single-ion Hydration and Ion Association in Aqueous Solutions ». University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439310243.
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Park, Sarah Sunah. « Electron- and ion-conducting metal-organic frameworks ». Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113983.
Texte intégralRésumé :
Thesis: Ph. D. in Inorganic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2017.Cataloged from PDF version of thesis. Vita.
Includes bibliographical references (pages 129-136).
This thesis focused on designing, characterizing and understanding the electronic or ionic behavior of electron- or ion-conducting metal-organic frameworks (MOFs). Chapter 1 gives a general introduction for electron- or ion-conducting MOFs, including a review of the reported materials exhibiting such behavior. Chapter 2 describes new MOFs designed using through-space charge transport strategies, as introduced in Chapter 1. Chapter 2 discusses four isostructural materials of general formula M2(TTFTB) (M = Mn, Co, Zn, and Cd), which exhibit infinite helical TTF stacks and reveal a correlation between the shortest intermolecular S ... S interaction among neighboring TTF cores and their single crystal conductivity. These results are the first demonstration of tuning intrinsic electrical conductivity of a MOF and provide a systematic blueprint for the design of throughspace charge transporting MOFs. Chapter 3 details the study of ligand-directed topologies in the material Mg₂H₆(H₃O)(TTFTB) 3 (MIT-25), obtained from H₄TTFTB, a ligand with a high propensity toward [pi]-stacking. Because understanding intermolecular [pi]-stacking interactions is important for designing through-space charge transport materials, we studied the significance of how the organic secondary building unit (SBU), which is energetically competitive with the formation of common inorganic SBUs, can also define MOF topology. Chapters 4 and 5 demonstrate examples of MOFs as ionic conductors. In Chapter 4, the proton conductivity of MIT-25 is studied. Owing to its large proton content and compositionally integral hydronium ion, MIT-25 exhibits an strongly hydrophilic environment that facilitates proton conduction. Lastly, Chapter 5 reports a Cu(II)-azolate MOF (MIT-20) with cylindrical pores, which undergoes a reversible single crystal-to-single crystal transition between neutral and anionic phases upon reaction with stoichiometric amounts of halide or pseudohalide salts. By utilizing this transformation, halide/pseudohalide anions are bound to the metal centers and become stationary, while the cations move freely within the one-dimensional pores, giving rise to single-ion Li+, Na+, or Mg²+ solid electrolytes.
by Sarah Sunah Park.
Ph. D. in Inorganic Chemistry
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You, Xingzhi. « An Advanced High Efficiency Non-Radiogenic Ion Source for Ion Mobility Spectrometry ». Diss., The University of Arizona, 2013. http://hdl.handle.net/10150/293471.
Texte intégralRésumé :
During the last decade, the Denton Research Group has made significant advancements in the field of real time direct vapor detection of low volatile explosives under ambient conditions. An ion source plays a crucial role in the sensitive detection of traces of compounds in gas phase by ion mobility spectrometry, but, all the current ionization techniques have significant drawbacks and do not fully satisfy all needs. To overcome the limitations associated with either hazards from a radiogenic ion source or poor reliability from the current non-radiogenic ion sources, the author of this dissertation has undertaken the development of an entirely new ion source based on dielectric barrier discharge technologies. This dissertation describes the development, characterization, and applications of novel dielectric barrier discharge (DBD) ion sources for ion mobility spectrometry. The sources under investigation are non-radiogenic, highly reliable, and provide a high yield of ions. The difficulty of extracting ion current from a traditional dielectric barrier discharge was solved by using an array of tiny discharges formed at the crossing points of two crossed sets of glass coated wires. The relationship of the excitation voltage, frequency, and extraction field for AC excitation on the extracted ion current were studied. The dielectric barrier discharge ion source were also excited in pulse mode by fast-rising and fast-falling high voltage pulses. A high voltage switch using serial MOSFETs was specially designed for driving the dielectric barrier discharge ion source in pulse mode. Application of this dielectric barrier discharge ion source to ion mobility spectrometry was demonstrated with the measurement of limit of detection and direct vapor detection of explosives.
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Radioti, Aikaterini. « Energetic ion composition and acceleration mechanisms in the magnetosphere of Jupiter ». Katlenburg-Lindau Copernicus GmbH, 2006. http://www.digibib.tu-bs.de/?docid=00011594.
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Buxton, Samuel. « Parasitic nematode ion channels : improving understanding of pharmacology and genetic composition ». Thesis, Tours, 2012. http://www.theses.fr/2012TOUR4047/document.
Texte intégralRésumé :
Actuellement, les infections des humains, des plantes et des animaux par les nématodes parasites ont un impact économique majeur. En l’absence de vaccin efficace, les anthelminthiques sont les principaux agents chimiothérapeutiques utilisés pour le traitement et la prophylaxie des infections à nématodes. Cependant, la résistance est apparue pour la plupart des anthelminthiques. Par conséquent il est urgent de comprendre la génétique des récepteurs ciblés par ces anthelminthiques et de trouver des cibles alternatives afin de développer de nouveaux anthelminthiques. Nous avons démontré les effets du nouvel anthelminthique cyclooctadepsipeptide, emodepside, sur le potentiel de membrane et les courants voltagedépendants chez le parasite du porc Ascaris suum. Enfin, nous avons cloné quatre gènes codant des sous-unités du récepteur de l'acétylcholine d'un autre parasite du porc, Oesophagostomum dentatum et caractérisé dans des ovocytes de Xenopus laevis quatre sous-types de récepteurs au lévamisoleParasitic nematode infections of humans, plants and animals are of major economic impact. Anthelmintics are the main chemotherapeutic agents used for treatment and prophylaxis of nematode infections because there is presently no effective vaccine on the market. However, resistance has been reported to the mainstay anthelmintics. There is therefore the urgent need to understand the genetics of the receptors targeted by these anthelmintics and to find alternative targets for developing new anthelmintics. We have demonstrated the effects of the new novelacting cyclooctadepsipeptide anthelmintic, emodepside, on the membrane potential and voltageactivated currents in the pig parasite Ascaris suum. Finally, we show the cloning of four acetylcholine receptor subunit genes from another pig parasite, Oesophagostomum dentatum and the expression and characterization of four levamisole receptor subtypes in Xenopus laevis oocytes
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Zankov, Ivan. « Optimization of Cubesat-Compatible Plasma Ion Analyzer for Asteroid Composition Analysis ». Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-76290.
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Many space probes have conducted in situ explorations of asteroids, in recent decades, intent on identifying evidence of the solar system's earliest processes of formation within the asteroids' interiors. Several future asteroid missions are planned, among which include ESA's Hera mission to explore the Didymos binary asteroid pair. An ion mass analyzer is currently being designed at the Swedish Institute of Space Physics for use as part of the Hera mission. This thesis aims to optimize the instrument such that each of its parameters meets the requirement for performance. A computer simulation is used to calculate the trajectories of low-energy ions inside the instrument, where the electrostatic potential are imposed by grids and electrodes embedded inside the instrument. From the data analysis of the simulation results, the performance for each parameter can be derived. By changing the settings of the grids and electrodes (e.g., positions and voltages), the instrument parameters are to be optimized. Two tasks are set up in this project--- the first task is to optimize the focusing system of the incoming ions at the instrument's entrance, and the second task is to investigate the reflectron system so that the mass resolution of the instrument can be optimized via reducing the spread of the ions' time of flight spectra. The focusing system is found to already be optimized, but instead, a relation between its position of the grid at the instrument's entrance and the instrument's performance is derived. The method of and parameters for optimization within the reflectron are extensively tested individually during this project. Although several performances in each trial from the reflectron analysis cannot meet at least one of the requirements, enough scenarios are examined such that every parameter tested ends with a value suitable to be applied individually to optimize the ion mass analyzer. The findings from the individual tests done in this project can be applied to further optimization, particularly to optimize multiple parameters simultaneously in the near future.
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Swallow, Isabella Diane. « Probes for bacterial ion channels ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:d42d13dd-dd0c-451b-bd00-e06f84350335.
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Using three complementary approaches, this work sought to tackle the widespread problem of antibiotic resistance. To circumvent the resistance mechanisms developed by bacteria, it is necessary to establish drug candidates that act on novel therapeutic targets, such as the ion channels used by bacteria to modulate homeostasis. Examples include the potassium efflux channel, Kef, and the mechanosensitive channel of small conductance, MscS, which are not found in humans. How these targets function must be well understood before drug candidates can be developed, as such, their identification and investigation is often accompanied by the evolution of the analytical techniques used to study them. Membrane protein mass spectrometry is one technique showing potential in the study of ion channels. However, spectra can be clouded by the detergents used to solubilise ion channels from their native membranes. Undertaken herein was the synthesis of some fluorescent glycolipid detergents, which it was hypothesised could be encouraged to dissociate from ion channels via laser-induced excitation within the gas phase of a mass spectrometer, thereby improving the clarity with which spectra can be obtained. For Kef, an unconfirmed mechanism of action had previously been proposed. To explore the suggestion that sterically-demanding central residues are important for channel activation, solid phase peptide synthesis was used to isolate three tripeptide analogues of N-ethylsuccinimido glutathione, a known activator with a high affinity for Kef. A competition fluorescence assay suggested these tripeptides bound to Kef with an affinity lower than predicted, allowing the conclusion that a more detailed assessment of the steric bulk required for activation was necessary before a mechanism of action could be confirmed. Lysophosphatidylcholine has been shown to activate MscS, although it is not known how. Affinity chromatography between MscS and lysophosphatidylcholine was proposed as a means by which specific binding interactions could be investigated. For this technique an amino-derivative of lysophosphatidylcholine was necessary and its challenging synthesis is also detailed herein.
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Kullman, Michael John. « Computional chemistry studies of gas-phase ion structures ». Thesis, Wichita State University, 2012. http://hdl.handle.net/10057/5412.
Texte intégralRésumé :
Computational chemistry and mass spectrometry are two extremely useful tools that when used in conjunction with each other allow detailed knowledge of the gas-phase ions. To that end, computational chemistry, specifically density functional theory is used for theoretical to experimental frequency comparisons. This allows for insight into the reaction pathways and likely structures to be explored in detail.Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry
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Boldi, Robert A. (Robert Arthur). « A model of ion chemistry of electrified convection ». Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/51502.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992.Includes bibliographical references (leaves 175-182) and index.
by Robert A. Boldi.
Ph.D.
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Zhang, Mengqi. « Thermodynamically Driven Ion Exchange between MS (M= Fe Zn) and the Cu2+ Ion : Towards a Safe Oral Copper Detoxifying Drug ». Kent State University Honors College / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1400279302.
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Dick, Janice. « Analytical applications of ion selective devices ». Thesis, University of Newcastle Upon Tyne, 1991. http://hdl.handle.net/10443/834.
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Ion selective electrodes, ISEs, and ion sensitive field effect transistors, ISFETs, are small, relatively simple to operate and easily automated sensors and, therefore, have a wide range of uses e. g. for field measurements in portable detectors, for on-line measurements in industrial flow systems and in clinical work. Several flow systems were studied for use with ion selective devices. New design ISE flow cells, designed at Newcastle, were found to minimise dead space and carry-over of sample solutions, allowing more rapid sample throughput. An ISFET flow cell studied, however, was found to have serious design faults. The constant volume dilution method of calibration and selectivity determination was shown to be a simple easy-touse method but must be implemented with caution. The selectivity of sensors to the primary ion was determined, where applicable, and the optical sensitivity of ISFETs was examined. Potassium concentrations in fertilizers were determined, using ISEs, in both flow systems described above; more accurate results were obtained using the newer flow-cells. Failure of ISEs after prolonged use in fertilizer solutions is believed to be have been caused by Donnan Breakdown due to HPO 2- ions. A computer controlled titration system was developed which can be used for volumetric or coulometric titrations. Coulometry, an absolute method, is particularly suitable for titration of sub micro-litre samples and for chemically labile species as sample manipulation is minimised and avoids addition of solution reagent, obviating CO 2 contamination of hydroxide. The advantages of coulometry were exploited in work to confirm the second dissociation constant for hydrogen sulphide. Aerial oxidation and sample carbon dioxide uptake are common problems associated with sulphide solutions. Using degassed water for sample preparation, keeping all solutions under nitrogen and using a sulphide anti-oxidant buffer it was possible to reduce sulphide oxidation. Coulometry was used to generate hydrogen ions and potentiometric measurements of the pH and sulphide ion concentrations, made simultaneously, were used to calculate the pK 2d of hydrogen sulphide for a range of 50 gl sodium sulphide solutions. A non-linear least squares programme, SUPERQUAD, was used to obtain a better value for pK 2d. Though a coulometric option exists in SUPERQUAD, it is not often implemented. ISE titration results have not been used much with SUPERQUAD; this work examined the potential of expanding the application of SUPERQUAD. Values of pK 2d of 12.08 ± 1.0 and 11.83 ± 0.4 were obtained by visual inspection and SUPERQUAD refinement, respectively. These values agree well with the text-book value, of 11.96, and demonstrate the accuracy of coulometry. The auto-titration system developed has advantages in many areas, particularly in clinical chemistry where determinations of available species in sub micro-litre samples, delivered in a flow system are required.
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Byrne, Declan J. « Novel calixarene receptors for ion complexation ». Thesis, Queen's University Belfast, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287294.
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O'Neill, Karen Elizabeth. « Studies in ion trap mass spectrometry ». Thesis, University of East Anglia, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332326.
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Grey, H. « Ion-selective electrodes using biomimetic ligands ». Thesis, University of Newcastle Upon Tyne, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372565.
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Johnson, Brian W. « Ion transport through protective polymer coatings ». Thesis, University of Newcastle Upon Tyne, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293683.
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Knipe, Peter Clarke. « Chiral counter-ion controlled asymmetric electrocyclic reactions ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:c981f724-c783-4913-b224-92fcebf94d37.
Texte intégralRésumé :
The aim of this project was to develop new catalytic methods to control asymmetry in electrocyclic reactions, and to apply these methods to generate complex molecules. Initial efforts were directed towards the catalysis of anionic 8π electrocyclizations (Chapter 2 and Figure i). 8π electrocyclization was not achieved due to issues with alkene geometry and anion stability. Our efforts were then directed towards using phase-transfer catalysis to generate complex polycyclic compounds via a cascade electrocyclization-1,4-addition (Chapter 3 and Figure ii). Pyrrolidines and indolizidines were generated in excellent yield from simple starting-materials with high levels of stereocontrol. Finally, we investigated the catalysis of a 6π [1,6] electrocyclization to generate dihydroquinolones (Chapter 4 and Figure iii). A novel BINOL-derived copper(II) catalyst was developed, and afforded dihydroquinolones directly from their amine and aldehyde precursors with good yields and enantioselectivities.
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Parker, Mariah L. « The Investigation of Oxidative Addition Reactions of Metal Complexes in Cross-Coupling Catalytic Cycles Based on a Unique Methodology of Coupled Ion/Ion-Ion/Molecule Reactions ». VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5651.
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Popular catalytic cycles, such as the Heck, Suzuki, and Negishi, utilize metal centers that oscillate between two oxidation states (II/0) during the three main steps of catalysis: reductive elimination, oxidative addition, and transmetallation. There has been a push to use less toxic, cheaper metal centers in catalytic cycles, leading to interest in first-row transition metals, such as nickel and cobalt. With these metals, the cycles can potentially pass through the +1 oxidation state, which acts as reactive intermediates, undergoing oxidative additions to form products, potentially with radical characteristics. The oxidative addition steps of catalytic cycles are critical to determining overall rates and products, however in many cases, these steps have not been amenable to study, in either condensed phase or gas phase, in the past. Through the use of electron transfer dissociation (ETD) technology on a modified Thermo Electron LTQ XLTM mass spectrometer, it is possible to generate intermediates in these catalytic cycles, including those in unusual oxidation states. Using sequentially coupled ion/ion-ion/molecule reactions, the reduced, reactive intermediate can be readily generated, isolated, and studied.As a model set of reactions, the mono- and bis-phenanthroline complexes of Fe(I), Co(I), Ni(I), Cu(I), and Zn(I) were formed by reduction of the corresponding M(II) species in an ion/ion reaction with the fluoranthenyl radical anion. The chemistry of the M(I) species was probed in ion/molecule reactions with allyl iodide. In order to explore ligand effects and the scope of oxidative addition reagents further, bipyridine and terpyridine were studied with these five first-row transition metal complexes while using an acetate series and other substrates for oxidative additions. Through these studies, the roles of the metal and ligand in dictating the product distributions and reaction rates were assessed. Metal electron count, ligand flexibility, and coordination number are critical factors. The overall reactivity is in accord with density functional theory calculations and mirrors that of proposed intermediates in condensed-phase catalytic cycles. In addition, second- and third-row transition metals (Ru(I), Pd(I), and Pt(I)) were explored with bipyridine, mono- and bis-triphenylphosphine, and 1,2-bis(diphenylphosphino)benzene ligation schemes. A variety of oxidative addition reagents were surveyed to determine the scope of reactivity and preference toward metal-carbon bond formation or carbon radical formation.
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Cool, Lydia R. « Identifying and Distinguishing Isomers Using Mass Spectrometry and Ion Mobility ». University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460470683.
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Chen, Songela Wenqian. « Modeling ion mobility in solid-state polymer electrolytes ». Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122534.
Texte intégralRésumé :
Thesis: S.B., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 31-32).
We introduce a course-grained model of ion diffusion in a solid-state polymer electrolyte. Among many tunable parameters, we investigate the effect of ion concentration, ion-polymer attraction, and polymer disorder on cation diffusion. For the conditions tested, we find that ion concentration has little effect on diffusion. Polymer disorder creates local variation in behavior, which we call "trapping" (low diffusion) and "free diffusing" (high diffusion) regions. Changing ion-polymer attraction modulates the relative importance of trapping and free diffusing behavior. Using this model, we can continue to investigate how a number of factors affect cation diffusion both mechanistically and numerically, with the end goal of enabling rapid computational material design.
by Songela Wenqian Chen.
S.B.
S.B. Massachusetts Institute of Technology, Department of Chemistry
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Bright, Vivien Bianca. « Street canyon atmospheric composition : coupling dynamics and chemistry ». Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4414/.
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A new model for the simulation of street canyon atmospheric chemical processing has been developed, by integrating an existing Large-Eddy Simulation (LES) dynamical model of canyon atmospheric motion with a detailed chemical reaction mechanism, the Reduced Chemical Scheme (RCS), comprising 51 chemical species and 136 reactions, based upon a subset of the Master Chemical Mechanism (MCM). The combined LES-RCS model is used to investigate both the effects of mixing and chemical processing upon air quality within an idealised street canyon. The effect of the combination of dynamical (segregation) and chemical effects is determined by comparing the outputs of the full LES-RCS canyon model with those obtained when representing the canyon as a zero-dimensional box model (i.e. assuming mixing is complete and instantaneous). The LES-RCS approach predicts lower (canyon-averaged) levels of NOX, OH and HO2, but higher levels of O3, compared with the box model run under identical chemical and emission conditions. Chemical processing of emissions within the canyon leads to a significant increase in the Ox flux from the canyon into the overlying boundary layer, relative to primary emissions, for the idealised case and a number of pollution scenarios considered. These results demonstrate that within-canyon atmospheric chemical processing can substantially alter the concentrations of pollutants injected into the urban canopy layer, compared with the raw emission rates within the street canyon and that such variations have a considerable effect on average within canyon concentrations and the flux of pollutants out of the canyon into the urban background environment.
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Du, Chen. « Architectural Characterization of Polyhedral Oligomeric Silsesquioxanes by Ion Mobility Mass Spectrometry ». University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525355186538632.
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Wade, David Christopher. « Investigating palaeoatmospheric composition-climate interactions ». Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/282998.
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The composition of the atmosphere has changed substantially over Earth's history, with important implications for past climate. A number of case studies will be presented which employ coupled climate model simulations to assess the strength of these chemical feedbacks on the climate. The eruption of Mount Samalas in 1257 led to the largest stratospheric volcanic injection of aerosol precursor gases in the Common Era, however climate model simulations of the last millennium typically overestimate the resulting climatic cooling when compared with tree-ring proxy records. A novel configuration of the Met Office UM-UKCA climate model is presented which couples an atmosphere-ocean general circulation model to a rigorous treatment of the relevant atmospheric chemistry and microphysical aerosol processes. This permits the climate response to a particular stratospheric injection of reactive volatile gases to be quantified and for the first time to date applied to a historical volcanic eruption. This model configuration compares favourably to observational data for simulations of the 1991Mount Pinatubo eruption. Results from an ensemble of model simulations are presented, with different assumptions about the sulfur dioxide and halogen loadings based on a recent geochemical reconstruction. These show a muted climate response, in reasonable agreement with tree ring records. Emissions of halogenated compounds lead to an increase in the sulfur dioxide lifetime, widespread ozone depletion and a prolonged climatic cooling. Strong increases in incident ultraviolet radiation at Earth's surface also occur. Oxygen levels may have varied fromas little as 10% to as high as 35% in the Phanerozoic (541Ma - Present). An increase in atmospheric oxygen increases atmospheric mass which leads to a reduction in incident shortwave radiation at Earth's surface due to Rayleigh scattering. However, this is offset by an increase in the pressure broadening of greenhouse gas absorption lines. Dynamical feedbacks also lead to increased meridional heat transport, warming polar regions and cooling tropical regions. An increase in oxygen content using the HadCM3-BL and HadGEM3-AO climate models leads to a global mean surface air temperature increase for a pre-industrial Holocene base case, in agreement with idealised 1D and 2D modeling studies. Case studies from past climates are investigated using HadCM3-BL which show that in the warmest climates, increasing oxygen may lead to a temperature decrease, as the equilibrium climate sensitivity is lower. For the Maastrichtian (72.1 - 66.0Ma), increasing oxygen content leads to a better agreement with proxy reconstructions of surface temperature at that time irrespective of the carbon dioxide content. There is considerable uncertainty in the timing of the rise in atmospheric oxygen content from values around 1% in the Neoproterozoic (1000 Ma - 541 Ma) to the 10- 35% values inferred in the Phanerozoic with respect to two global glaciation episodes (717-635Ma). Results of simulations with HadCM3-BL which investigate the impact of oxygen content on the Neoproterozoic Snowball Earth glaciations are presented. These demonstrate that a smaller reduction in carbon dioxide content is required to initiate a Snowball Earth at low oxygen content. Geological evidence suggests the presence of a basaltic large igneous province before the Sturtian Snowball Earth episode. This could have caused episodes of paced explosive volcanism, injecting sulfate aerosol precursors into the stratosphere. Results of simulations to investigate the impact of different volcanic aerosol emission scenarios are presented. 500 Tg SO2 is investigated with a range of aerosol sizes. For aerosol size distributions consistent with the aerosol evolution in the aftermath of the Mount Pinatubo eruption, the Earth enters a Snowball Earth in between 30 and 80 years. Using a larger size of aerosols, consistent with a larger eruption, does not lead to a Snowball Earth. These simulations show that changes to the chemical composition of the atmosphere, whether reactive gases or bulk chemical composition may have played an important role in the past climate of Earth.
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Van, Orden Steven Lee. « Mechanistic investigations of gas phase ion-molecule reactions using Fourier transform ion cyclotron resonance mass spectrometry ». Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186137.
Texte intégralRésumé :
Studies of the mechanisms and energetics of a variety ion-molecule reactions involving organometallic and organic ions, have been performed using Fourier transform ion cyclotron resonance mass spectrometry (FTMS). The bond activation processes of V⁺, VO⁺, VOH⁺, and VOCH₃⁺ with water and methanol were investigated in detail. All ions are observed to preferentially activate the C-O bond in methanol, however C-H and O-H bond cleavage are also observed. The addition of the oxo, hydroxo, and methoxo ligands is found to significantly effect the intrinsic reactivity of the ions, relative to V⁺. The reactions of V(CO)₅⁻ with a wide variety of molecules have revealed mechanistic details of the oxidative addition and ligand switching reactions. Steric effects are proposed to account for the selective reactivity of V(CO)₅⁻ with alcohols and amines. Studies of ligand substitution reactions support an electron transfer initiated mechanism, implying that V(CO)₅⁻ has a triplet ground state and a trigonal bipyramidal structure. The chlorine atom transfer reactions of V(CO)₅⁻ with chloromethanes display a correlation with C-CI bond strength, suggesting the mechanism is initiated by oxidative addition of the C-C1 bond or involves a direct chlorine atom transfer. The decomposition of metallocarboxylate anions ([M(CO)ₓ₋₁CO₂]⁻) was studied in an effort to understand the production of CO₂ by metal carbonyl compounds, proposed as intermediates in the Water-Gas shift reaction. The nascent [M(CO)ₓ₋₁C0₂]⁻*, formed by nucleophilic addition of 0⁻ to M(CO)ₓ (M=Pe, Cr, V), is observed to undergo exclusive loss of CO₂ without subsequent decomposition of the product metal carbonyl anion (M(CO)ₓ₋₁⁻) The reaction of P AHs with O⁻ and O₂⁻ were studied, to investigate the potential of isomer differentiation by chemical ionization. These reactions are characterized by a number of reactive pathways, demonstrating the ability to distinguish isomers which cannot be differentiated by other ionization techniques. Kinetic energy release measurements of the S(N)2 reactions of F⁻ with CH3CI, C₆H₅CI, and CH₃COCl have been made using KEICR. The F⁻/CH₃Cl reaction results in a non-statistical energy disposal. The reaction is proposed to proceed by a direct mechanism.
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Carey, Kieran A. « New chemistry of bis-trityl dications ». Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311995.
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Myung, Sunnie. « Developing ion mobility methods for studying structure and assembly of biomolecules ». [Bloomington, Ind.] : Indiana University, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3238509.
Texte intégralRésumé :
Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2006."Title from dissertation home page (viewed July 16, 2007)." Source: Dissertation Abstracts International, Volume: 67-10, Section: B, page: 5718. Adviser: David E. Clemmer.
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Willemse, Abraham Cilliers. « Electrospinning bicomponent nanofibres for platinum ion extraction from acidic solutions ». Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80028.
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Thesis (MSc)--Stellenbosch University, 2013.ENGLISH ABSTRACT: Trace amounts of soluble Pt(II/IV) ions are not recovered using current refining processes. There are both economic and environmental incentives to recover these Pt(II/IV) ions from effluent. The work presented in this dissertation was aimed at producing functionalised electrospun nanofibre webs for the extraction of trace amounts of Pt(II/IV) ions in the form of [PtCl6]2- from acidic solutions. An insoluble, low molecular weight oligomeric compound, poly(N-terephthaloylthiourea)-N’,N’-piperazine, was synthesised from relatively inexpensive starting reagents using a “one-pot” two step synthesis procedure. Interest in this compound lies in its ability to extract Pt(II/IV) ions from acidic, chloride-rich solutions, as may be encountered in real process solutions in platinum group metal refineries. The product was isolated and characterised with an array of techniques, including GPC, elemental analysis, 1H and 13C NMR, as well as FTIR, and it was found to be a mixture of various molecular weight fractions with a degree of chemical variance between oligomer chains. The poly(N-terephthaloylthiourea)-N’,N’-piperazine was blended with polyacrylonitrile (PAN) and electrospun using both the classical single needle approach as well as a high throughput free-surface electrospinning process, called ball electrospinning. The nanofibres consisted of the oligomer which provided the affinity for [PtCl6]2- while PAN provided sufficient polymer chain entanglement which allowed the formation of fibrous structures. Two different solutions were found to produce nanofibres with the desired dimensions, namely: 6 wt% and 8 wt% PAN solution, both having a PAN to oligomer ratio of 7:3. The fibres produced by needle electrospinning and ball electrospinning had average fibre diameters of 172 ± 35 nm and 210 ± 49 nm, respectively. The ball electrospinning process had 86 times greater fibre production rates compared to needle electrospinning. The effects of three experimental conditions on the recovery of Pt(II/IV) ions by the poly(N-terephthaloylthiourea)-N’,N’-piperazine-containing nanofibres were determined. The conditions were: (i) the effects of specific surface area and available coordination sites over time, (ii) the effect of extraction temperature, and (iii) the effect of hydrochloric acid (HCl) concentration on [PtCl6]2- extraction. Increased availability of coordination sites caused an increase in Pt ion extraction. The Pt ion extraction also increased from 0.007 g to 0.023 g for each gram of nanofibres used as the temperature was increased from 20 °C to 60 °C when using a 114 mg/L Pt stock solution. The HCl concentration had no effect on Pt ion extraction when varied between 1.0 x 10-3 M to 1 M, while increased extraction as well as fibre damage was caused at HCl concentrations greater than 1 M. Nanofibres containing an oligomeric compound with affinity for [PtCl6]2- in acidic solutions were successfully synthesised and used to extract trace amounts of Pt(II/IV) ions from solutions under various conditions.
AFRIKAANSE OPSOMMING: In huidige verfynings prosesse word spoorelemente van oplosbare Pt(II/IV) nie herwin nie. Daar is beide ekonomiese en omgewings insentiewe om hierdie Pt(II/IV) ione te verhaal uit die afval oplossings. Hierdie tesis was gemik daarop om funksionele elektrospinde nanovesel webbe te produseer vir die herwinning van Pt(II/IV) ioon spoorelemente in die vorm van [PtCl6]2- uit aangesuurde oplossings. ‘n Onoplosbare oligomeriese verbinding met ‘n lae molukulêre gewig, poly(N-terephthaloylthiourea)-N’,N’-piperazine, was uit relatief goedkoop begin reagense gesintetiseer deur gebruik te maak van ‘n “een-pot” twee stap prosedure. Die belangrikheid van die verbinding lê in sy vermoë om Pt(II/IV) ione uit aangesuurde, chloried-ryke oplossing te onttrek, soos wat in alledaagse afval oplossings van platinum-groep metalurgiese raffinaderye ondervind kan word. Die sintese produk was geisoleer en gekarakariseer deur gebruik te maak van ‘n verskeidenheid tegnieke, waaronder GPC, elementêre analise, 1H en 13C NMR sowel as FTIR, en daar was bepaal dat die produk bestaan uit ‘n mengsel van verskeie molukulêre gewig kettings met ‘n mate van chemiese variansie tussen hulle. Die gesintetiseerde oligometriese verbinding was gemeng met poliakrielonitriel (PAN) en elektrospin deur gebruik te maak van beide die klasieke naald spin proses, sowel as ‘n hoë-produksie vrye oppervlak spin proses, genaamd die bal elektrospin proses. Die nanovesels bestaan uit die oligomeer wat die affiniteit vir die [PtCl6]2- voorsien terwyl die PAN genoegsame polimeer ketting verstrengeling veroorsaak het om die veselagtige struktuur te vorm. Nanovesels met die gewensde dimensies was gevorm deur die elektrospin proses toe te pas op twee verskillende oplossings, naamlik: ‘n 6 massa persent PAN en ‘n 8 massa persent PAN oplossing, beide met ‘n PAN tot oligomeer verhouding van 7:3. Die vesels geproduseer deur die naald en bal elektrospin prosesse het ‘n gemiddelde vesel deursneë gehad van 172 ± 35 nm en 210 ± 49 nm, onderskeidelik. Die bal spin proses het egter ‘n 86 keer groter produksie kapasiteit van vesels gehad in vergelyking met die naald spin proses. Die effek van drie verskillende toestande op die effektiwiteit van die nanovesels, wat poly(N-terephthaloylthiourea)-N’,N’-piperazine bevat, om Pt(II/IV) ione te onttrek uit die oplossings was ondersoek. Die toestande was: (i) die effekte van spesifieke oppervlak area asook beskikbare ontginnings setels oor tyd, (ii) die effek van die ontginnings temperatuur, en (iii) die effek van die soutsuur (HCl) konsentrasie op die Pt ioon ontginning. ‘n Toename in die beskikbaarheid van die ontginnings setels het gelei tot ‘n toename in die Pt ioon ontginning. Die Pt ioon ontginning het toegeneem van 0.007 g tot 0.023 g vir elke gram van nanovesels gebruik soos die temperatuur verhoog was van 20 °C tot 60 °C wanneer ‘n 114 ppm (m/v) Pt ioon oplossing gebruik was. Daar was geen effek op die Pt ioon ontginning toe die HCl konsentrasie tussen 1.0 x 10-3 M en 1 M HCl varieer was nie, alhoewel daar by konsentrasies hoër as 1M ‘n verhoogde ontginning sowel as vesel skade was. Nanovesels wat ‘n oligemetriese verbinding bevat met ‘n affiniteit vir [PtCl6]2- in ‘n aangesuurde oplossing, was suksesvol gesintetiseerd en gebruik om spoorelemente van Pt(II/IV) te onttrek onder verskillende omstandighede.
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Cullen, Thomas Donovan. « Hydroxyl radical reaction and lanthanide ion complexation kinetics of DTPA ». Thesis, California State University, Long Beach, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1524188.
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