Made available in DSpace on 2018-08-01T21:58:48Z (GMT). No. of bitstreams: 1 tese_10611_Flavia Tosato.pdf: 3350639 bytes, checksum: 70973978751713caf9a8020e18b13280 (MD5) Previous issue date: 2016-12-09 / Análises rápidas, baratas e eficientes são necessárias para as rotinas laboratoriais, principalmente quando aplicada em química forense. As utilizações de fontes ambientes permitem que as análises sejam diretas e rápidas. Assim, são opções inovadoras para melhorar a sensibilidade e seletividade. Neste trabalho, foi desenvolvida uma metodologia utilizando a espectrometria de massas ambiente por paper spray ionization mass spectrometry (PS-MS) para diferentes matrizes de dados: (i) identificar e quantificar cocaína e seus adulterantes a partir da cromatografia em camada delgada acoplada ao PS-MS; (ii) realizar a discriminação ou classificação de dez marcas brasileiras de cervejas em pilsen e lager; e (iii) identificar a falsificação controlada de Uisque com cachaça visando quantificar o volume de cachaça adicionado na mistura. Na análise de cocaína e adulterantes, os padrões foram identificados na CCD e analisados por PS-MS, e uma curva de calibração foi otimizada. A cerveja foi previamente fracionada usando a metodologia de extração em fase sólida (SPE) com água/metanol e os quatro extratos foram caracterizados no modo positivo de ionização, PS(+)MS. Para ambos os casos, foram aplicados de 20 µL do analito sobre a superfície do papel do PS-MS. Na quantificação de cachaça em misturas de whisk-cachaça. Os resultados indicam que, utilização da CCD acoplado ao PS-MS possibilita a identificação de cocaína e seus adulterantes uma ótima linearidade paras as curvas foi encontrada (cocaína (R2 = 0,9989), benzocaína, (R2 = 0,9934), a cafeína (R2 = 0,9988), a fenacetina (R2 = 0,9966), e a lidocaína (R2 = 0,9987)) e LOD inferior ao da técnica de CCD. Para as amostras de cerveja os sinais de açúcares se sobressaem sobre os demais grupos, e após a extração com água/metanol foi possível distinguir os espectros das diferentes marcas de cervejas e classifica-las em pilsen e lager pela técnica de PCA. Utilizando o PS(±)-MS e PLS com seleção de variáveis foi possível estimar quantitativamente o teor de cachaça misturado ao uísque. Com isso, utilização de fontes ambientes, como PS mostra-se eficaz para identificação de diversas matrizes, facilitando as análises de rotina.

Electromagnetic shock tubes were used to generate plasmas having a number density of the order of 10¹⁷ per cm³ and an energy per particle of 1-3 ev. In the shock tubes employed, the driving current was passed via electrodes through a discharge at one end of the tube. The discharge gases that were driven down the shock tube plus the ambient gas that was picked up and heated constituted the plasma that was studied. Many workers have assumed that shock equations can describe the discontinuity at the front of the plasma. An investigation into the effects of changes in the geometry of the driver mechanism has disclosed that the luminosity structure that can be attributed to the discharge gases stays very close to the luminosity front. The amount of ambient gas that is entrained in front of the discharge gases is thus small. Therefore, some doubt exists about the applicability of the shock equations both in the present shock tube and in the electromagnetic shock tubes of other workers. The shape of the luminosity front of the plasma was found to be affected by the properties of the driving discharge, even at a time long after the driving current had ceased to flow. Instabilities of the discharge and contamination by electrode material were found to drastically affect the homogeneity of the plasma. The homogeneity and reproducibility of the plasma produced by a small-cathode driver were found to be fairly good. However, there was a large amount of contamination in the plasma. The plasma was used to investigate the electro-dynamic response of an inductive magnetohydrodynamic power generator. Expressions for the output power were derived and compared with the experimental results. The electrodynamical response of a novel electrode-type Bɵ magnetohydrodynamic power generator was calculated. In an experiment performed with this generator a magnetohydrodynamic Interaction was observed indicating that the plasma was transporting an azimuthal magnetic field. No output power was obtained. The probable cause for this was that the applied magnetic field was insufficient to break down the sheath on the electrodes. A low pressure spark gap switch suitable for use as a main switch and as a "crowbar" switch on a capacitor bank was developed. The switch was operated over a voltage range of 0.5 to 25 kV, at energies up to 4 kJ and currents up to 500 kA. Under normal operating conditions the triggering time was 40 nsec and the jitter approximately 10 nsec. The inductance of the main switch was 4 nH and the inductance of the crowbar switch was about 1 nH. Other contributions are presented on a wide-voltage-range open-air spark gap switch, high voltage trigger circuits and on the dynamics of the plasma in an electromagnetic shock tube. The latter consists of an elementary treatment of the electromagnetic acceleration processes and a proposal of a model for the decelerating plasma. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A potentiometric method which is devised to be rapid and convenient for determining ionization constants for water, weak acids (or bases), and certain solids in mixed solvents is described. The method has been applied to the determination of ionization for water, acetic acid, benzoic acid, and phenol and the solubility product constant for silver chloride in mixtures of water with methanol, ethanol, acetone, tetrahydrofuran, and p-dioxane containing from 0 to 70 mass percent organic co-solvent at several temperatures between 10 and 40°C. Results are used to study the thermodynamics of ionization in each mixture which is discussed relative to various topics of ion-ion, ion-solvent, ion-molecule, molecule-solvent, and solvent-solvent interactions on the basis of theories of electrostatics, salvation, and solvent and solution structure. A calorimetric technique applied to the investigation of dimerization of benzoic acid, m-toluic acid, and o-toluic acid in benzene and toluene at 25°C as a preliminary study of the author is briefly mentioned in Appendix E.

Much important work has been done to understand reaction pathways and identify products, yields, and reaction rates for atmospheric oxidation processes. Non-methane hydrocarbons (NMHCs) are the most significant of the organic compounds present in the atmosphere from a chemical perspective and are released into the atmosphere from both natural and anthropogenic sources. The oxidation of these hydrocarbons by hydroxyl radical HO generates products that may themselves be toxic, that play a major role in the formation of photochemical smog, and that to a lesser extent contribute to the formation of acid precipitation. NMHCs have chemical reactivities many times that of methane, the most abundant HC in the atmosphere. However, the atmospheric oxidation processes of less than 50% of atmospheric NMHCs are known. A new experimental technique is needed that can provide insight into atmospheric oxidation products, reaction intermediates, and the relative importance of secondary reaction pathways that follow the initial attack of HO upon a hydrocarbon. The technique should operate at atmospheric pressure to better represent natural reaction processes and conditions, and provide a rapid and direct measure of product identities and yields. In this study we will describe the development and application of a technique that we believe meets these requirements, a technique we call High Resolution Kinetic Atmospheric Pressure Ionization Mass Spectrometry (HRKAPIMS). We begin with the use of atmospheric pressure ionization mass spectrometry in studies of atmospheric oxidation processes. We first describe a potential pitfall in the use of APIMS for the analysis of smog chamber experiments, a common APIMS application, discussing methods to eliminate interference reactions that would otherwise make interpretation difficult. A new experimental approach to the use of APIMS for the analysis of oxidation processes is next described and its use demonstrated. The oxidation of toluene by API source-generated HO produces oxidation products that are protonated and detected by the mass spectrometer. With this approach, we observe all the products found in a variety of previous studies employing a large array of experimental setups and analytical instrumentation. This is significant because our experiments are carried out in a far simpler experimental environment. Toluene is chosen for these experiments because it is an important constituent in polluted urban atmospheres with a complex oxidation mechanism that remains poorly understood. We describe the development of HRKAPIMS, a powerful new approach that allows the simultaneous detection of stable products along with free radical intermediates. The use of nitric oxide to affect product yields is demonstrated, giving valuable insights into reaction kinetics and mechanisms. We also address the theoretical aspects of HRKAPIMS, describing semiempirical calculations to estimate gas-phase basicities for a wide variety of compounds and discuss the errors implicit in this approach. The use of gas-phase basicities is discussed in terms of mass spectrometric analysis and analyte response. Kinetic and thermodynamic modeling is used to address the issues of APIMS and HRKAPIMS sensitivity and response and gain insights into the conditions necessary for linear response and quantitative detection of analytes.

No description available.

Part A of two Project Reports; Part B can be found at: http://hdl.handle.net/11375/17692 / <p> A number of recently published papers have been critical of the values of CE and Cλ by the ICRU as absorbed dose conversion factors for ionization chambers used in electron or photon beams.</p> <p> This report examines the subject in light of these recent works. Presented is a review of both theoretical and experimental results published to date along with the results of experimental work carried out at this facility. The present study concentrated on the measurement of the absorbed dose conversion factors for electrons and 25 NW photons. It also attempted to determine how the conversion factors might be influenced by such factors as chamber design buildup cap thickness and composition, and phantom composition.</p> <p> Measurements were made using electrons with 10 to 32 MeV initial energy and a 25 MeV photon beam, all produced by a Sagittaire Model Therac 40 linear accelerator. Checks on the stability of the measurement system were made using a 60Co source. Fricke ferrous sulfate dosimetry was used for absorbed dose measurement in the determination of CE.</p> <p> The results of the study would indicate that there is little or no effect on the measured values of CE or Cλ introduced by either the sleeves or phantoms for the radiation qualities studied. The results of the absorbed dose conversion factor study would indicate that the values recommended by the ICRU are sufficiently accurate for use in most instances. The data would tend to support the arguement that if there is an error in one of the ICRU derivations, the error in theory lies in the CE determination rather than that for Cλ.</p> / Thesis / Master of Engineering (MEngr)

No description available.

Sensitivity Sⁱ_p is defined as the ratio of the fractional change of gas ionization current to the fractional change of gas pressure. A maximum obtainable sensitivity was calculated, Sⁱ_p]_max = -0.309 A/B V, where A, B are constants for a given gas within a particular range of field-to-pressure ratio. Experiments were conducted to investigate the sensitivity of air and krypton under different combinations of voltage, electrode separation and primary electron source strength. A curie of tritium placed on the central portion of either electrode produced a constant initial emission current and a high sensitivity. Sensitivity could be increased by using a stronger current source, higher voltage and a larger electrode separation. Observed values of Sⁱ_p for high voltage at larger separation are greater than those expected even when breakdown occurs at a (pd) quite larger than the one for Sⁱ_p]_max. The fractional pressure change, Δp/p, is independent of the initial pressure, p, and is greater for a heavier gas subject to the same acceleration, a fact which suggests the use of a heavier gas to obtain a higher fractional current change for the same sensitivity. Krypton behaves in a similar way as air in the system. Operating current level may be higher than 10⁻⁵ ampere if stronger source is used. There is a limit in the separation for a given source configuration. Further increase in Sⁱ_p and current level may be achieved through better design of the configuration and location of the current source between the electrodes. The fractional current change, Δi/i, depends more on Δp rather than on the initial operating pressure, p. From the experiment performed, it appears that a gas system will perform satisfactorily as a transient velocity gauge. / M.S.

Incident 0.5 to 2.5 MeV charged particle beams were used to ionize the inner-shells of selected targets and study their subsequent emission of characteristic x-rays. ⁹Be⁺ ions were used to examine K-shell x-ray production from thin F, Na, Al, Si, P, Cl, and K targets, L-shell x-ray production from thin Cu, An, Ge, Br, Zr and Ag targets, and M-shell x-ray production from thin Pr, Nd, Eu, Dy, Ho, Hf, W, Au, Pb and Bi targets. L-shell x-ray production cross sections were also measured for ²⁷Al⁺ ions incident upon Ni, Cu, Zn, As, Zr, and Pd targets. M-shell x-ray production cross sections were measure for ²⁷Al⁺ and ⁴⁰Ar⁺ ions incident upon Pr, Nd, Gd, Dy, Lu, Hf, Au, Pb, Bi, and U targets. These measurements were performed using the 2.5 MV Van de Graaff accelerator at North Texas State University. The x-rays were detected with a Si(Li) detector whose efficiency was determined by fitting a theoretical photon absorption curve to experimentally measure values. The x-ray yields were normalized to the simultaneously measured Rutherford backscattered (RBS) yields which resulted in an x-ray production cross section per incident ion. The RBS spectrum was obtained using a standard surface barrier detector calibrated for to account for the "pulse height defect." The experimental results are compared to the predictions of both the first Born and ECPSSR theories; each of which is composed of two parts, the direct ionization (DI) of the target electron to the continuum and the capture (EC) of the target electron to the projectile. The first Born describes DI by the Plane-Wave-Born-Approximation (PWBA) and EC by the Oppenheimer-Brinkman-Kramers treatment of Nikolaev (OBKN). ECPSSR expands upon the first Born by using perturbed (PSS) and relativistic (R) target electron wave functions in addition to considering the energy loss (E) of the projectile in the target and its deviation from straight line trajectory (Coulomb deflection (C)). The measurements presented show that the first Born theories overestimate the measured results rather significantly for all experiments using the ⁹Be beams to examine the inner shell x-rays, while the ECPSSR predictions fir the measured data much better. For incident ²⁷Al and ⁴⁰Ar ions, the measured results are not predicted by the theories. The first Born generally over-predicts the data for low target atomic numbers while under-predicting at high atomic numbers. The ECPSSR theory greatly under-predicts the results (factors of 10³ to 10²⁰). Reasons for this behavior are discussed as well as suggestions for future experiments.

The K-shell x-ray and ionization cross sections are measured for protons on Ag, Cd, Sn, Sb, Te, Ba, and La over the ion energy range of 0.6 to 2.0 MeV. The data are compared to the predictions of the PWBA, the PWBA with corrections for binding energy and/or Coulomb deflection, the BEA, and the constrained BEA predictions. In general, the non-relativistic PWBA with binding energy correction gives the best overall agreement with the measurements of proton-induced x-ray processes for the K-shell of the elements studied in this work. The data further suggest the need for relativistic PWBA treatment of the interactions in the K-shell for the range of binding energies represented by the elements investigated in this work.