A procedure for evaluating the precision of atomic absorption measurements is presented and applied to 21 elements under varying instrumental conditions. The experimental relative standard deviations (RSD's) in absorbance obtained from repetitive measurements made with a high resolution voltmeter and on-line computer, are compared to those predicted by a recently proposed theoretical equation. Good agreement between theory and experiment is obtained which indicates the usefulness of the theoretical equation and evaluation procedure. The study reveals that, under the conditions used for atomic absorption measurements for the 21 elements, the noise associated with the lamp (i.e., signal shot noise and source flicker noise) and with the flame (i.e., flame transmission flicker noise) limit the precision at small absorbances (i.e., A < 0.1 ). Flame transmission flicker noise generally increases with the flame absorbance. Over most of the analytically useful range of absorbances (i.e., 0.1 > A > 1.0-1.5) analyte absorption flicker limits the precision to a value near 1% RSD for one second integration periods. The precision can be improved by a factor of two to three for any absorbance region with ten second integration periods, although not much better than this with any longer integration periods. Precision at high absorbances (i.e., A > 1.0-1.5) is limited by emission noises (analyte and background). For longer wavelengths, the analyte emission noises become more significant. The limiting noises' frequency dependence is obtained with noise power spectra and analyte absorption, emission, and fluorescence flicker are shown to all have a similar 1/f (inverse frequency) character, as well as a value of about 1% for the RSD for Cu. Abbreviated procedures for evaluation of noise in atomic emission (AE) and atomic fluorescence measurements are presented. Other studies into the source of analyte absorption noise are presented, and the conclusion is drawn that this flicker noise is probably due to nebulization fluctuations, non-fundamental in nature. The study of these various noise sources' dependence on the instrumental parameters (e.g. burner position, slit height and width, flame type and stoichiometry, and lamp current) suggest how to optimize conditions or concentrations so that an analysis can be carried out with maximum precision. / Graduation date: 1978

Graduation date: 1996

Graduation date: 1995

Thesis (M.S.)--Brigham Young University. Dept. of Physics and Astronomy, 2006. / Includes bibliographical references (p. 93-95).

Thesis (Ph. D.)--University of Washington, 1983. / Vita. Bibliography: leaves [115]-123.

Ce travail de thèse est consacré à la réalisation et à la prédiction des données d’adsorption physique sous pression sur différents adsorbants carbonés poreux comme les charbons actifs ou les tamis moléculaires carbonés. Le choix de ces adsorbants tient compte de la nécessité de disposer d’échantilons microporeux suffisamment différenciés. Ce travail a été réalisé dans le but d’apporter une contribution à la compréhension des mécanismes d’adsorption en corps pur et en mélanges dans des conditions hautement non- idéales et pour des matériaux hétérogènes en prenant essentiellement en compte les paramètres de la texture poreuse et les paramètres del’adsorbat en phase gazeuse et en phase adsorbée. Cette démarche nous permet en suite d’étudier le degré del’hétérogénéité structurale des adsorbants carbonés. Un appareillage volumétrique en mode statique a été mis au point dans le but de collecter des mesuresd’adsorptionencorps purs. Une étude rigoureuse des incertitudes sur cet appareillage a permis la quantification des erreurs sur chaque paramètre expérimental afin d’estimer l’erreur totale sur la masse adsorbée. Une étude comparative avec un autre appareillage gravimétrique en mode statique a permis de mettre en évidence les performances de nos outils de mesure dans ce travail. Les isothermes d’adsorption de l’azote,de l’argon, du méthane et del’oxygène à haute pression ont été obtenues sur cinq différents adsorbants carbonés. Les isothermes ont été collectées à différentes températures permettant la détermination des chaleurs isostériques par application de l’équationde Clausius-Clapeyron. Les résultats obtenus sont en parfait accord avec les résultats de caractérisation. Nous avons ensuite proposé de confronterl’ensemble de ces mesures à notre modèle de thermodynamique statistique basé sur la notion d’équation intégrale d’adsorption. Nous avons proposé d’étudier l’influence du choix du potentiel d’énergie d’adsorption sur les performances du modèle en corps pur. Cette confrontation expérience théorie a permis d’extraire les paramètres de la fonction de distribution du volume des pores de chaque adsorbant ainsi que les paramètres relatifs au comportement de l’adsorbat en phase adsorbée. Nous proposons l’extension directe du modèle à l’étude des équilibres en mélanges sans détermination de paramètre supplémentaire. Enfin des mesures en mélanges binaires sur un appareillage en mode statique, couplant volumétrie et chromatographie, ont été réalisées pour étudier les performances de notre modèle. Nous proposons par analogie à l’étude des corps purs une analyse rigoureuse des incertitudes sur cet appareillage. L’ensemble de ce travaila permis de mettre en évidence les performances de notre modèle basé sur les caractéristiques structurales des adsorbants pour étudier les équilibres en corps purs et en mélanges, et cela dans de larges gammes de conditions non-idéales qui sont les conditions requises dans la plupart des applications industrielles (procèdes de séparation (PSA), stockage en phase adsorbée à haute pre sion du gaz naturel et de l’hydrogène,etc

Heparin, a highly sulfated and acidic glycosaminoglycan, has been clinically used in parenteral formulations to prevent and/or treat thromboembolic disorders for more than 90 years. Actions of heparin are not limited to anticoagulation and antithrombosis. Rather heparin has several other important actions which include fat clearing, antitumor and anti-inflammatory effects. However, use of heparin for such applications has been limited by its route of administration.<p> Historically, it has been believed that heparin is not absorbed following oral administration and therefore is only available for clinical use by parenteral administration. This belief has been challenged several times by our laboratory and other researchers showing heparin binding to endothelium following oral administration as well as prevention of thrombosis and lowering blood pressure, etc. However, the site of oral heparin absorption and the mechanism responsible for absorption have not been investigated. This in vitro study was designed to address these important questions.<p> We mounted pieces of rat gastrointestinal mucosa in a vertical diffusion Ussing chamber with both sides of the mucosal membrane exposed to Krebs bicarbonate buffer solution containing mannitol on the mucosal side (lumen) and glucose on the serosal side. Electrical properties across the membrane including potential difference (PD), resistance (R), and short circuit current (Isc) were recorded following heparin addition to the mucosal buffer under different mucosal buffer pH conditions. Mucosal and serosal buffer and tissue were collected and extracted for heparin and heparin recovery was performed by gel electrophoresis and anticoagulation tests. The first chapter (chapter 4) was designed to investigate if stomach mucosal tissue is a site for unfractionated heparin (UFH) absorption when mounted in the Ussing chamber. We found that stomach mucosa is able to transport UFH in an intact form when both mucosal and serosal buffers are at neutral pH of 7.4. When the mucosal buffer pH is made more acidic, at pH 4, transport is facilitated.<p> The second study (chapter 5) was designed to investigate if stomach mucosal tissue is also capable of transporting low molecular weight heparins (LMWHs). We showed that LMWHS were transported across stomach mucosa. However, the rate of transport was faster at mucosal buffer pH of 7.4 compared to pH 4.<p> The third study (chapter 6) investigated the effect of molecular weight on rate of heparin transport across stomach mucosal tissue since pH dependency of this transport was evident from both previous studies. This study suggested that decreasing the molecular weight increases the rate of heparin transport across stomach tissue under neutral pH but not acidic pH conditions. The fourth study (chapter 7) investigated how UFH is transported across the ileal mucosa and if Peyers patches contribute to this transport. It was shown that UFH is transported across ileal mucosa containing Peyers patches at a rate faster than ileal mucosa without Peyers patches. Making the mucosal buffer pH acidic facilitated UFH transport in the absence of Peyers patches but not when ileal mucosa contained Peyers patches.<p> The final study (chapter 8) investigated the mechanism of UFH transport across stomach mucosa mounted in the Ussing chamber using pharmacological inhibitors sodium fluoride, colchicine, and amiloride. Results showed that UFH is transported across the stomach mucosa at physiological acidic pH by an active transport mechanism using metabolic energy, cytoplasmic tubule formation, and sodium-coupled systems. From this, we conclude that oral heparins are absorbed across the gastrointestinal tract. The acidic environment of the stomach is a better absorption site for UFH. On the other hand, the more basic environment of the intestine is a better site for absorption of LMWHs. UFH is mainly absorbed across the stomach mucosa by an active transport mechanism using metabolic energy, cytoplasmic tubule formation, and sodium-coupled systems. Considering the very much larger surface area of the intestine than the stomach and that intestine, especially the ileum, contains many Peyers patches where UFH transport is not pH-dependent, larger amounts of UFH may be transported across the intestinal tissue compared to the stomach.

No description available.

Heparin, a highly sulfated and acidic glycosaminoglycan, has been clinically used in parenteral formulations to prevent and/or treat thromboembolic disorders for more than 90 years. Actions of heparin are not limited to anticoagulation and antithrombosis. Rather heparin has several other important actions which include fat clearing, antitumor and anti-inflammatory effects. However, use of heparin for such applications has been limited by its route of administration.<p> Historically, it has been believed that heparin is not absorbed following oral administration and therefore is only available for clinical use by parenteral administration. This belief has been challenged several times by our laboratory and other researchers showing heparin binding to endothelium following oral administration as well as prevention of thrombosis and lowering blood pressure, etc. However, the site of oral heparin absorption and the mechanism responsible for absorption have not been investigated. This in vitro study was designed to address these important questions.<p> We mounted pieces of rat gastrointestinal mucosa in a vertical diffusion Ussing chamber with both sides of the mucosal membrane exposed to Krebs bicarbonate buffer solution containing mannitol on the mucosal side (lumen) and glucose on the serosal side. Electrical properties across the membrane including potential difference (PD), resistance (R), and short circuit current (Isc) were recorded following heparin addition to the mucosal buffer under different mucosal buffer pH conditions. Mucosal and serosal buffer and tissue were collected and extracted for heparin and heparin recovery was performed by gel electrophoresis and anticoagulation tests. The first chapter (chapter 4) was designed to investigate if stomach mucosal tissue is a site for unfractionated heparin (UFH) absorption when mounted in the Ussing chamber. We found that stomach mucosa is able to transport UFH in an intact form when both mucosal and serosal buffers are at neutral pH of 7.4. When the mucosal buffer pH is made more acidic, at pH 4, transport is facilitated.<p> The second study (chapter 5) was designed to investigate if stomach mucosal tissue is also capable of transporting low molecular weight heparins (LMWHs). We showed that LMWHS were transported across stomach mucosa. However, the rate of transport was faster at mucosal buffer pH of 7.4 compared to pH 4.<p> The third study (chapter 6) investigated the effect of molecular weight on rate of heparin transport across stomach mucosal tissue since pH dependency of this transport was evident from both previous studies. This study suggested that decreasing the molecular weight increases the rate of heparin transport across stomach tissue under neutral pH but not acidic pH conditions. The fourth study (chapter 7) investigated how UFH is transported across the ileal mucosa and if Peyers patches contribute to this transport. It was shown that UFH is transported across ileal mucosa containing Peyers patches at a rate faster than ileal mucosa without Peyers patches. Making the mucosal buffer pH acidic facilitated UFH transport in the absence of Peyers patches but not when ileal mucosa contained Peyers patches.<p> The final study (chapter 8) investigated the mechanism of UFH transport across stomach mucosa mounted in the Ussing chamber using pharmacological inhibitors sodium fluoride, colchicine, and amiloride. Results showed that UFH is transported across the stomach mucosa at physiological acidic pH by an active transport mechanism using metabolic energy, cytoplasmic tubule formation, and sodium-coupled systems. From this, we conclude that oral heparins are absorbed across the gastrointestinal tract. The acidic environment of the stomach is a better absorption site for UFH. On the other hand, the more basic environment of the intestine is a better site for absorption of LMWHs. UFH is mainly absorbed across the stomach mucosa by an active transport mechanism using metabolic energy, cytoplasmic tubule formation, and sodium-coupled systems. Considering the very much larger surface area of the intestine than the stomach and that intestine, especially the ileum, contains many Peyers patches where UFH transport is not pH-dependent, larger amounts of UFH may be transported across the intestinal tissue compared to the stomach.

No description available.