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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Comparação entre analisadores com fluxo constante ou pulsado: aplicação a amostras de relevância farmacêutica, agronômica e/ou ambiental / Comparison of flow analyzers exploiting constant or pulsed flows: application to samples of pharmaceutical, agronomical and/or environmental relevance

Sasaki, Milton Katsumi 24 November 2015 (has links)
Sistemas de análises químicas em fluxo com multi-impulsão empregam bombas solenoide como unidade propulsora de fluidos, as quais proporcionam fluxos pulsados. Estes provêm um eficiente transporte radial de massas, o que garante boa homogeneização das soluções envolvidas, mesmo em situações de dispersão limitada. O objetivo principal deste trabalho foi então comparar o desempenho de metodologias envolvendo reagentes imobilizados em sistemas de análises em fluxo com fluxos constantes ou pulsados. Para isto, foram selecionadas as determinações espectrofotométricas de ácido ascórbico em produtos farmacêuticos, utilizando reator tubular de polietileno (50 cm) com MnO2(s) imobilizado, e reação com formaldoxima (0,25 mol L-1); e de carbaril em águas naturais, explorando extração líquido-líquido com xileno imobilizado em membrana de PVDF, e solução de NaOH a 0,1 mol L-1 como fluxo aceptor. Adicionalmente, compararam-se os dois tipos de fluxo em uma nova titulação em fluxo, a titulação monitorada por traçador; a determinação de acidez total em vinagres foi selecionada e utilizaram-se as titulações por injeção em fluxo e programada em triângulo, ambas empregando solução de NaOH a 0,01 mol L-1 como titulante e fenolftaleína como indicador ácido-base, com monitoramento por traçador empregando azul brilhante FCF (ca. 6 mg L-1). Na determinação de ácido ascórbico, o desempenho do sistema com fluxos pulsados foi superior àquele com fluxos constantes quanto ao limite de detecção: 0,33 contra 0,60 mg L-1 (critério 3,3 ?), e à repetibilidade: d.p.r. estimado como 2,5 contra 5,6% (n = 20); quanto à exatidão, não foi encontrada diferença estatisticamente significativa entre o método proposto e o da Farmacopeia Britânica ao nível de confiança de 95%. Na determinação de carbaril, o uso de fluxos pulsados favoreceu a extração do analito, obtendo-se uma sensibilidade 9,3% maior relativamente ao emprego de fluxos constantes, além de uma melhor linearidade da curva analítica; entretanto, o método mostrou-se susceptível a interferência de outros metilcarbamatos, o que comprometeu sua aplicação à análise de águas naturais. Na determinação de acidez total, a exploração de fluxos pulsados proporcionou menores variações da razão dos valores de absorbância relativos ao monitoramento do traçador e do indicador; não foi encontrada diferença estatística entre as titulações em fluxo propostas e o método titulométrico de referência ao nível de confiança de 95% / Multi-pumping flow systems use solenoid pumps as fluid propelling devices, which deliver pulsed flows. These flows provide an efficient radial mass transport, thus good mixing conditions even in limited sample dispersion situations. The main objective of this work was then to compare the performance of methodologies involving immobilized reagents in flow systems with constant or pulsed flows. To this end, the spectrophotometric determinations of ascorbic acid in pharmaceutical products using a 50-cm polyethylene tubular reactor with immobilized MnO2(s) with further colour-forming reaction with 0.25 mol L-1 formaldoxime; and carbaryl in natural waters exploiting liquid-liquid extraction with xylene immobilized in a PVDF membrane and a 0.1 mol L-1 ¬¬NaOH solution as acceptor stream, were selected. Moreover, constant and pulsed flows were compared in relation to a novel strategy for flow titration, named tracer-monitored titration; the determination of total acidity in vinegars was selected and flow injection and triangle-programmed titrations were applied, both using a 0.01 mol L-1 NaOH solution as titrant, phenolphtalein as acid-base indicator and ca. 6 mg L-1 brilliant blue FCF as tracer. Regarding ascorbic acid determination, the pulsed flow system was superior in relation to the constant flow system for detection limit: 0.33 against 0.60 mg L-1 (3.3 ? criterion), and for repeatability: r.s.d. estimated as 2.5 against 5.6% (n = 20); in relation to accuracy, no significant differences between the proposed method and that of the British Pharmacopoeia were found at the 95% confidence level. Regarding carbaryl determination, use of pulsed flows favored the analyte extraction, leading to a 9.3% sensitivity improvement in relation to use of constant flows; besides the attainment of better linearity of the analytical curve. The method was however susceptible to interference of other methylcarbamates, thus the application to natural water analyses was impaired. Regarding total acidity determination, pulsed flows exploitation provided lower variations in the ratio of absorbance values related to the monitoring of tracer and indicator; no significant differences between the proposed titrations and the reference method were found at the 95% confidence level
12

Comparação entre analisadores com fluxo constante ou pulsado: aplicação a amostras de relevância farmacêutica, agronômica e/ou ambiental / Comparison of flow analyzers exploiting constant or pulsed flows: application to samples of pharmaceutical, agronomical and/or environmental relevance

Milton Katsumi Sasaki 24 November 2015 (has links)
Sistemas de análises químicas em fluxo com multi-impulsão empregam bombas solenoide como unidade propulsora de fluidos, as quais proporcionam fluxos pulsados. Estes provêm um eficiente transporte radial de massas, o que garante boa homogeneização das soluções envolvidas, mesmo em situações de dispersão limitada. O objetivo principal deste trabalho foi então comparar o desempenho de metodologias envolvendo reagentes imobilizados em sistemas de análises em fluxo com fluxos constantes ou pulsados. Para isto, foram selecionadas as determinações espectrofotométricas de ácido ascórbico em produtos farmacêuticos, utilizando reator tubular de polietileno (50 cm) com MnO2(s) imobilizado, e reação com formaldoxima (0,25 mol L-1); e de carbaril em águas naturais, explorando extração líquido-líquido com xileno imobilizado em membrana de PVDF, e solução de NaOH a 0,1 mol L-1 como fluxo aceptor. Adicionalmente, compararam-se os dois tipos de fluxo em uma nova titulação em fluxo, a titulação monitorada por traçador; a determinação de acidez total em vinagres foi selecionada e utilizaram-se as titulações por injeção em fluxo e programada em triângulo, ambas empregando solução de NaOH a 0,01 mol L-1 como titulante e fenolftaleína como indicador ácido-base, com monitoramento por traçador empregando azul brilhante FCF (ca. 6 mg L-1). Na determinação de ácido ascórbico, o desempenho do sistema com fluxos pulsados foi superior àquele com fluxos constantes quanto ao limite de detecção: 0,33 contra 0,60 mg L-1 (critério 3,3 ?), e à repetibilidade: d.p.r. estimado como 2,5 contra 5,6% (n = 20); quanto à exatidão, não foi encontrada diferença estatisticamente significativa entre o método proposto e o da Farmacopeia Britânica ao nível de confiança de 95%. Na determinação de carbaril, o uso de fluxos pulsados favoreceu a extração do analito, obtendo-se uma sensibilidade 9,3% maior relativamente ao emprego de fluxos constantes, além de uma melhor linearidade da curva analítica; entretanto, o método mostrou-se susceptível a interferência de outros metilcarbamatos, o que comprometeu sua aplicação à análise de águas naturais. Na determinação de acidez total, a exploração de fluxos pulsados proporcionou menores variações da razão dos valores de absorbância relativos ao monitoramento do traçador e do indicador; não foi encontrada diferença estatística entre as titulações em fluxo propostas e o método titulométrico de referência ao nível de confiança de 95% / Multi-pumping flow systems use solenoid pumps as fluid propelling devices, which deliver pulsed flows. These flows provide an efficient radial mass transport, thus good mixing conditions even in limited sample dispersion situations. The main objective of this work was then to compare the performance of methodologies involving immobilized reagents in flow systems with constant or pulsed flows. To this end, the spectrophotometric determinations of ascorbic acid in pharmaceutical products using a 50-cm polyethylene tubular reactor with immobilized MnO2(s) with further colour-forming reaction with 0.25 mol L-1 formaldoxime; and carbaryl in natural waters exploiting liquid-liquid extraction with xylene immobilized in a PVDF membrane and a 0.1 mol L-1 ¬¬NaOH solution as acceptor stream, were selected. Moreover, constant and pulsed flows were compared in relation to a novel strategy for flow titration, named tracer-monitored titration; the determination of total acidity in vinegars was selected and flow injection and triangle-programmed titrations were applied, both using a 0.01 mol L-1 NaOH solution as titrant, phenolphtalein as acid-base indicator and ca. 6 mg L-1 brilliant blue FCF as tracer. Regarding ascorbic acid determination, the pulsed flow system was superior in relation to the constant flow system for detection limit: 0.33 against 0.60 mg L-1 (3.3 ? criterion), and for repeatability: r.s.d. estimated as 2.5 against 5.6% (n = 20); in relation to accuracy, no significant differences between the proposed method and that of the British Pharmacopoeia were found at the 95% confidence level. Regarding carbaryl determination, use of pulsed flows favored the analyte extraction, leading to a 9.3% sensitivity improvement in relation to use of constant flows; besides the attainment of better linearity of the analytical curve. The method was however susceptible to interference of other methylcarbamates, thus the application to natural water analyses was impaired. Regarding total acidity determination, pulsed flows exploitation provided lower variations in the ratio of absorbance values related to the monitoring of tracer and indicator; no significant differences between the proposed titrations and the reference method were found at the 95% confidence level
13

Etude thermodynamique de la sorption de l'uranyle sur la monazite et la magnétite / Thermodynamic study of uranyl sorption onto lanthanum monophosphate (LaPO4) and magnetite (Fe3O4)

Felix, Olivia 10 July 2012 (has links)
Les phénomènes d’adsorption interviennent dans les processus géochimiques gouvernant ainsi le transport des contaminants. Par ailleurs, les variations de température sont susceptibles d’influencer significativement leur comportement vis-à-vis de la surface des minéraux. Aussi, l'influence de la température sur la sorption doit être étudiée afin de mieux appréhender le devenir des éléments dans l'environnement. Dans cette optique, l'interaction entre un ion modèle, l'uranyle et deux minéraux a été étudiée. Dans un premier temps, un composé méthodologique, la monazite, a été choisi afin de déterminer la démarche à suivre pour étudier l'influence de la température sur la sorption de l'uranyle dans trois milieux plus ou moins complexants. Puis, des tests préliminaires ont été réalisés pour étudier la sorption de l'uranyle sur un composé d'intérêt industriel, la magnétite, en appliquant la démarche mise en place. Le solide a d'abord été caractérisé d'un point de vue massif puis les caractéristiques acido-basiques de sa mise en suspension dans les trois électrolytes (NaClO4, NaNO3 et Na2SO4) ont été étudiées en fonction de la température. Les constantes d'équilibre associées aux réactions de déprotonation des sites de surface ont été déterminées entre 25°C et 95°C par modélisation de courbes de titrages potentiométriques. Les simulations ont été effectuées en limitant au maximum le nombre de degrés de liberté du système. Le modèle 1-pK a donc été préféré au modèle 2-pK en raison du nombre de paramètres ajustables plus limité dans ce modèle. Des contraintes expérimentales telles que le pH de point de charge nulle ou les enthalpies déterminées par mesure directe des chaleurs associées par microcalorimétrie de mélange ont été imposées pour déterminer les constantes d'équilibre acido-basiques. La sorption de l'uranyle en fonction du pH sur le même intervalle de température a été étudiée en alliant l'acquisition de données macroscopiques telles que les sauts de sorption et la spéciation en solution à une étude structurale menée par analyse par spectrofluorimétrie laser permettant l'identification des espèces sorbées. La simulation des sauts de sorption permettant d'accéder aux constantes associées aux réactions de sorption a été réalisée en imposant les caractéristiques acido-basiques préalablement déterminées. Des mesures directes, par microcalorimétrie de mélange, des chaleurs mises en jeu lors de la sorption de l'uranyle ont permis de tester la validité de la loi de Van't Hoff sur ce phénomène. La même démarche a été suivie pour étudier l'influence de la température sur la sorption de l'uranyle sur la magnétite en milieu NaClO4 et NaNO3. Cependant, l'étude structurale par spectrofluorimétrie laser n'a pu être réalisée en raison de la couloration noire de la magnétite. / The migration of radiotoxic elements in the geosphere is mainly regulated by chemical parameters which control the partitioning of the elements between mineral phases and aqueous solutions. Variation in temperature may affect the retention properties of a mineral surface and requires a careful investigation in order to understand the radionuclides behavior in the geosphere. In this way, the interaction mechanisms between uranium(VI) and two minerals (LaPO4 and Fe3O4) have been studied. In a first step, the monazite (LaPO4) has been chosen as methodological solid in order to clearly define all the different stages needed to completely characterize the influence of temperature on the sorption phenomena. To reach that goal, three media, more or less complexants towards aqueous uranyl and the mineral surface, have been considered. Physico-chemical as well as surface acid-base properties of the solid surface have been studied by considering three electrolytes (NaClO4, NaNO3 and Na2SO4) and temperatures ranged from 25°C to 95°C. The point of zero charge has been found to be identical for perchlorate and nitrate media (pHPZC=2.1) but it was found to be one pK unit higher for the sulfate medium indicating a sorption of the background electrolyte ions. The reaction heats associated to the hydration of the solid have been measured by using microcalorimetry and the nature of the reactive surface sites has been determined by carrying out Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS). On the basis of these experimental constraints, the titration curves obtained for the monazite suspensions were fitted by using the Constant Capacitance Model and the 1-pK model was preferred to characterize the surface charge evolution, due to the limited number of adjustable parameters. The surface protonation constants being determined, the behavior of U(VI) towards the monazite surface in the three electrolytes has been investigated. On the basis of both U(VI) speciation in solution and the results of a structural study carrying out by using TRLFS together with calorimetric measurements, the sorption edges have been modeled and the corresponding sorption constants determined. Since these values take into account a wide number of experimental results (both structural and thermodynamical ones) they appear to be accurate and could be extrapolated more confidently to other physico-chemical conditions. The experimental approach being validated with the methodological solid, preliminary tests have been carried out to study uranyl sorption onto a second substrate, the magnetite, more relevant than monazite in the field of radionuclides migration in the geosphere.

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