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Class of 2012 Abstract / Specific Aims: To assess the chemical stability of ampicillin for injection in normal saline at pH values ranging from 5 to 6. Methods: A stability-indicating high performance liquid chromatography (HPLC) method was developed and used to determine the stability of ampicillin for injection in normal saline following buffering with sodium acetate and acid adjustment with HCl at pH values of 5, 5.5, and 6. To confirm that the assay was stability-indicating, ampicillin trihydrate reference standard (1 mg/mL) was exposed to alkali, acid, and oxidative stress conditions and analyzed by HPLC for the presence of degradation products. Analysis was performed on a reverse-phase (C-18) column with a mobile phase consisting of water, acetonitrile, 1 M monobasic potassium phosphate, and 1 N acetic acid (909:80:10:1). Other HPLC parameters were: flow rate 1 mL/min; detection wavelength 254 nm; injection volume 20 μL; column temperature 30 ̊C. The method was evaluated for linearity, precision, and accuracy. The chemical stability of ampicillin for injection (18 mg/mL) in normal saline and sodium acetate (pH adjusted at values of 5, 5.5, and 6) was assessed at baseline (t=0), 7, 11, 17, 31, and 44 hours and compared to a control solution (no pH adjustment). Measurements at each time interval were performed in triplicate. Main Results: Ampicillin trihydrate reference standard (1 mg/mL) was adequately separated from degradation products following exposure to alkali, acid, and oxidative stress conditions. After 16 hours, a precipitate was observed in the solution at pH 6, and therefore stability is not reported. All other solutions (pH 5, pH 5.5, and control) were stable for at least 24 hours at room temperature and yielded t90 values of 110, 64.2, and 27.5 hours, respectively. Conclusions: Adjustment of intravenous ampicillin solutions to pH values of 5 or 5.5 significantly increased stability. Ampicillin appears to be most stable at a pH near its isoelectric point (pH 5).

In this thesis, we focus on the structural identification of the interface using surface enhanced Raman spectroscopy (SERS) and inelastic electron tunnelling scattering (IETS). Two different molecular junctions, namely gold/ trans-1,2-bis (4-pyridyl) ethylene/gold junction and gold/4,4'-bipyridine/gold junctions in various conditions were studied and the corresponding configurations were determined. The enhancement in SERS was also studied by employing the time-dependent density functional theory. Furthermore, we studied some properties of the interface, such as the stability of the adsorbates and charge transfer properties of molecular junctions. The decrease in the stability of molecules was found when adsorbed on metallic surface and trapped in metallic junctions. Our studies explained several puzzles and by rational design, more stable molecular devices were obtained.

Class of 2009 Abstract / OBJECTIVES: The objective of this study was to investigate the effects of temperature excursions on insulin during standard shipping from mail-order pharmacies. METHODS: Twelve vials of insulin (six of regular and six of neutral protamine hagedorn (NPH)) were sampled at baseline and then the six experimental vials (three regular and three NPH) were shipped through the mail system from a Tucson, Arizona post office to a Tucson, Arizona residence. The other six vials were used as controls and left in a refrigerator at 5°C. Samples were taken daily and then measured for degradation using high performance liquid chromatography (HPLC). Also, samples from control vials were put in a lab oven at a constant temperature of 48°C and analyzed at Day 0 and Day 2. RESULTS: Temperatures spiked daily to near or over 50°C with a peak of 51.5°C. The low temperature never dropped under 21°C. The area under the curve (AUC) for each individual sample drawn was used to calculate a percentage of its original concentration with Day 1 set as 100%. On Day 6, both experimental vials and control vials had similar results and were within 10% of the original concentrations measured. In the oven, NPH samples that were heated for two days lost about 4% of its concentration while the regular insulin sample lost 14%. Particle sizing data of regular insulin heated in the oven was consistent with this HPLC data, and showed significant shifts in peak position. CONCLUSIONS: Insulin appears to maintain its stability after being shipped through the mail and remaining in a mailbox for an additional five days at high summer temperatures in Arizona. However, when exposed to constant high temperatures in a laboratory oven, heat appears to affect its stability.

This diploma thesis is focused on determining the physico-chemical stability of toothpastes. It is divided into theoretical and practical part. The theoretical part of the work deals with toothpastes, their short history and composition. Stability studies and methods of stability analysis are described below. In the practical part were performed long-term and accelerated stability studies on anhydrous toothpastes, on water-based toothpastes and on toothpastes based on sodium bicarbonate. The physical stability of the products was evaluated by monitoring the appearance and color visually and odor sensory, the pH value using a pH meter and the viscosity with a rotational viscometer. Chemical stability was monitored by determining the free fluorine content by ion chromatography and by ion-selective electrode, total phosphates and potassium also by ion chromatography, sodium bicarbonate by titration, soluble zinc by atomic absorption spectrometry and water activity was also monitored.

A determinação da concentração de cloro residual livre nas soluções de hipoclorito de sódio é de fundamental importância para obtenção de resultados na clínica e na pesquisa. No presente estudo, foram avaliadas soluções de hipoclorito de sódio nas concentrações de 0.5%, 1%, 2.5% e 5%, preparadas a partir de outra solução concentrada. Atingidas as concentrações desejadas, ajustou-se o pH de 168 amostras em 7, 9 e 11 com ácido bórico. As amostras foram mantidas refrigeradas (5 ºC ± 1 ºC) e após 7, 14, 35, 49, 63, 91 e 120 dias avaliou-se, por meio da titulometria iodométrica, a concentração de cloro residual livre nas soluções estudadas. A análise dos resultados permitiu inferir que o pH e o tempo de armazenagem exercem influência sobre a estabilidade química das soluções de hipoclorito de sódio nas diversas concentrações estudadas e que a perda do teor de cloro é proporcional ao aumento da concentração. Em relação ao pH observou-se que, quando em pH 7, as soluções de hipoclorito de sódio em todas as concentrações avaliadas expiraram sua estabilidade química em tempo inferior a 7 dias, enquanto em pH 9, as soluções de hipoclorito de sódio em todas as concentrações avaliadas expiraram sua estabilidade química em tempo inferior a 35 dias, exceto para as soluções a 0.5% que se mantiveram estáveis durante todo o período experimental e, quando em pH 11, as soluções de hipoclorito de sódio em todas as concentrações avaliadas apresentaram estabilidade química por 120 dias, pois se mantiveram dentro dos limites estabelecidos durante todo o período experimental. Diante disso, sugere-se ao clínico a utilização de soluções de hipoclorito de sódio com valores de pH ajustados em 11 devido à sua maior estabilidade química. / The stability of sodium hypochlorite solutions is an important factor that may adversely affect the clinical and researchfull results. In this study we evaluated sodium hypochlorite solutions (0.5%, 1.0%, 2.5%, 5.0%) obtained from a concentrated solution. Once the required concentration was obtained, the pH of 168 samples was adjusted to 7.0, 9.0 e 11.0 with boric acid. The samples were stored in the refrigerator (5 °C ± 1 °C). After 7, 14, 35, 49, 63, 91 and 120 days, the concentration of free residual chlorine in the studied solutions was assessed by iodometric titration. The analysis of the results allowed to conclude that pH and storage time had an effect in the chemical stability of sodium hypochlorite solutions and the decomposition rate increases with the concentration. Considering the pH values this study showed that at pH 7.0 the chemical stability of sodium hypochlorite solutions was maintained for less than a week. At pH 9.0 all studied solutions maintained their chemical stability for less than 35 days, except the 0.5% solutions that exhibited higher available chlorine content during all experimental period. At pH 11.0 all studied solutions maintained their chemical stability during all experimental period. Hence, sodium hypochlorite solutions with pH 11.0 should be more frequently used due to their chemical stability.

Kinetics of the reactions of amoxycillin sodium and potassium clavulanate alone and in combination were investigated in the liquid and frozen states at selected pH values of 2.0, 4.6 and 7.0. A stability indicating HPLC assay was developed to perform simultaneous quantification of these compounds validated under stressed conditions.Amoxycillin and clavulanate degradation obeyed first-order kinetics under all conditions of this study. The effect of temperature, buffer, concentrations and complexation were investigated. Both compounds showed acceleration in rates due to general acid catalysis from buffer species. The buffer catalysis rate constants due to total phosphate and total acetate at 55 degrees celsius were 5.84x10(subscript)-1 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 and 1.53 X10(subscript)-1 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 for amoxycillin, 2.33 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 and 4.4x10(subscript)-1 mol dm(subscript)-3)(subscript)-1 h(subscript)-1 for clavulanate respectively. The buffer independent rate constant values were obtained and interpreted according to the available literature data. Increase in the initial concentration of amoxycillin or clavulanate did not change the first-order rate constant values of these antibiotics significantly at liquid state temperatures. However in the buffer systems, the rate of hydrolysis of amoxycillin in the combination was significantly subject to clavulanate catalysis. This novel finding was influenced by phosphate buffer concentration. A kinetic model was proposed and the second-order catalytic rate constant values at pH 7.0 and 55 degrees celsius were estimated for clavulanate catalysis of amoxycillin (k(subscript)cvc) to be k(subscript)cvc = 1.75 X10(subscript)2 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1 and for phosphate catalyzed of clavulanate catalysis of ++ / amoxycillin (k(subscript)phccv) as k(subscript)phccv = 2.87 (mol dm(subscript)-3)(subscript)-1 h(subscript)-1.The temperature dependence of the rate of amoxycillin sodium degradation over the pH range evaluated did not change significantly. However the E(subscript)a values of potassium clavulanate decreased slightly with increase in pH. Both the compounds showed similar E(subscript)a values at pH 4.6 in acetate system. Hence 71.2 kJ mol(subscript)-1 for amoxycillin and 75.1 kJ mol(subscript)-1 for clavulanate.The investigation on complexation effects by HPbetaCD on the rate of hydrolysis of amoxycillin and clavulanate indicated no significant change in the rate of reaction of amoxycillin in the acetate buffer system. But the rate of clavulanate hydrolysis in combination was decreased by approximately 10%. The rate constant within the cyclodextrin complex and the stability constant of the complex obtained for clavulanate at pH 4.6 and 55 degrees celsius were k(subscript)c = 1.54x 10(subscript)-1 h(subscript)-1 and K(subscript)c = 74.2 (mol dm(subscript)-3)(subscript)-1.Extrapolation of the rate constant values to the frozen state from the liquid state data indicated marked acceleration of the rate of amoxycillin and clavulanate in all the pH values investigated. The highest acceleration in rate recorded was 15.0 fold for clavulanate in the hydrochloric acid system and the lowest value was 4.4 fold for amoxycillin at -7.3 degrees celsius. The rate constant values obtained were interpreted in terms of the concentration model (Pincock and Kiovsky 1966), phase-temperature relationship of the solutes, buffer catalysis, pH change and polymerization reactions.In the hydrochloric acid system a kinetic model was deduced providing adequate explanation of the experimental results. The stabilizing effect of sodium chloride used for maintaining constant ionic strength (mu=0.5) was ++ / enormous in this system. The shelf-life of amoxycillin was increased from 2.2 h to 58.3 h at -7.3 degrees celsius when sodium chloride was included in the system. It also stabilized the rates of the reactions significantly in the buffer systems.The buffer systems used in this study stabilized the rates of the reaction of both the drug compounds considerably. The shelf-life of amoxycillin in phosphate buffer was 621.3 h at -13.5 degrees celsius and in acetate buffer the shelf-life of clavulanate was 71.9 h at the same temperature. These are the highest shelf-life values recorded so far in the literature for amoxycillin and clavulanate at this frozen temperature.

Anion exchange membrane fuel cells (AEMFCs) are an alternative to proton exchange membrane fuel cells (PEMFCs) with potential benefits that include low cost (i.e., platinum-free), facile electro-kinetics, low fuel crossover, and use of CO-resistant metal catalysts. Despite these advantages, AEMFCs have not been widely used because they require more highly conductive anion exchange membranes (AEMs) that do not exhibit impaired physical properties. Therefore, the issues that this research is dealing with are to maximize conductivity and to improve chemical stability. As model materials for these studies, I synthesize a series of multiblock copolymers with which polymer structures and morphologies can be easily controlled. Chapter 2 presents the synthesis and the chemical structure determination of the multiblock copolymers. With the objective of maximizing conductivity, an understanding of the impact of structural features such as organization, size, polarity and connectivity of ionic domains and channels within AEMs on ion/water transporting properties is necessary for the targeted and predictable design of an enhanced material. Chapters 3 to 5 describe three characterization techniques that reveal the role of these structural features in the transport process. Specifically, Chapter 3 demonstrates the possibility that the NMR relaxation times of water could be an indicator of the efficiency of ion channels. Low-temperature DSC measurements differentiate the state of water (i.e., bound water and free water) inside the membranes by measuring freezing temperature drop and enthalpy. Chapter 4 demonstrates that the number of water molecules in each state correlates with conductivity and suggests a major anion-conducting mechanism for the multiblock AEM systems. In Chapter 5, the measurement of the activation energy of diffusion characterizes ion transporting behavior that occurs on the sub-nanometer scale. For the characterization of the chemical stability of the AEMs under high pH conditions, I employ automated 1H NMR measurements as a function of time as well as diffusion-ordered NMR spectroscopy (DOSY) as shown in Chapter 6. Finally, I demonstrate that new multiblock copolymers are successfully utilized as an ionomer for a hybrid cell in Chapter 7. The properties of the polymer strongly influence overall cell performance. I believe that the combination of the techniques presented in this thesis will provide insight into the ion/water transporting mechanism in a polymer ion conductor and guidance for improving conductivity and the chemical stability of the AEMs.

A determinação da concentração de cloro residual livre nas soluções de hipoclorito de sódio é de fundamental importância para obtenção de resultados na clínica e na pesquisa. No presente estudo, foram avaliadas soluções de hipoclorito de sódio nas concentrações de 0.5%, 1%, 2.5% e 5%, preparadas a partir de outra solução concentrada. Atingidas as concentrações desejadas, ajustou-se o pH de 168 amostras em 7, 9 e 11 com ácido bórico. As amostras foram mantidas refrigeradas (5 ºC ± 1 ºC) e após 7, 14, 35, 49, 63, 91 e 120 dias avaliou-se, por meio da titulometria iodométrica, a concentração de cloro residual livre nas soluções estudadas. A análise dos resultados permitiu inferir que o pH e o tempo de armazenagem exercem influência sobre a estabilidade química das soluções de hipoclorito de sódio nas diversas concentrações estudadas e que a perda do teor de cloro é proporcional ao aumento da concentração. Em relação ao pH observou-se que, quando em pH 7, as soluções de hipoclorito de sódio em todas as concentrações avaliadas expiraram sua estabilidade química em tempo inferior a 7 dias, enquanto em pH 9, as soluções de hipoclorito de sódio em todas as concentrações avaliadas expiraram sua estabilidade química em tempo inferior a 35 dias, exceto para as soluções a 0.5% que se mantiveram estáveis durante todo o período experimental e, quando em pH 11, as soluções de hipoclorito de sódio em todas as concentrações avaliadas apresentaram estabilidade química por 120 dias, pois se mantiveram dentro dos limites estabelecidos durante todo o período experimental. Diante disso, sugere-se ao clínico a utilização de soluções de hipoclorito de sódio com valores de pH ajustados em 11 devido à sua maior estabilidade química. / The stability of sodium hypochlorite solutions is an important factor that may adversely affect the clinical and researchfull results. In this study we evaluated sodium hypochlorite solutions (0.5%, 1.0%, 2.5%, 5.0%) obtained from a concentrated solution. Once the required concentration was obtained, the pH of 168 samples was adjusted to 7.0, 9.0 e 11.0 with boric acid. The samples were stored in the refrigerator (5 °C ± 1 °C). After 7, 14, 35, 49, 63, 91 and 120 days, the concentration of free residual chlorine in the studied solutions was assessed by iodometric titration. The analysis of the results allowed to conclude that pH and storage time had an effect in the chemical stability of sodium hypochlorite solutions and the decomposition rate increases with the concentration. Considering the pH values this study showed that at pH 7.0 the chemical stability of sodium hypochlorite solutions was maintained for less than a week. At pH 9.0 all studied solutions maintained their chemical stability for less than 35 days, except the 0.5% solutions that exhibited higher available chlorine content during all experimental period. At pH 11.0 all studied solutions maintained their chemical stability during all experimental period. Hence, sodium hypochlorite solutions with pH 11.0 should be more frequently used due to their chemical stability.

Glassy carbon is a disordered form of carbon with very high temperature resistance, high hardness and strength and chemical stability even in extreme environments. Glassy carbon is also unaffected by nearly all acids and cannot be graphitized even at very high temperature. Because of these characteristics, there is a possibility that glassy carbon can replace copper, iron, titanium alloys and other materials employed in making canisters used in nuclear waste storage. The modification of glassy carbon due to strontium ions implantation and heat treatment is reported. Glassy carbon (GC) samples were implanted with 200 keV strontium ions to a fluence of 2×1016 ions/cm2 at room temperature. Sequential isochronal annealing was carried out on the implanted samples at temperatures ranging from 200 oC - 900 oC for one hour. The influence of ion implantation and annealing on surface topography was examined by the scanning electron microscopy (SEM), while Raman spectroscopy was used to monitor the corresponding structural changes induced in the glassy carbon. The depth profiles of the implanted strontium before and after annealing were determined using Rutherford Backscattering Spectroscopy (RBS). Compared to SRIM predictions the implanted strontium profiles was broader. After annealing at 300 oC, bulk and surface diffusion of the strontium atoms took place. Annealing at 400 oC- 700 oC not only resulted in further diffusion of strontium towards the surface, the diffusion was accompanied with segregation of strontium on the surface of the glassy carbon substrate. Evaporation of the strontium atoms was noticed when the sample was annealed at 800 oC and 900 oC respectively. These annealing temperatures are higher than the melting point of strontium (~769 oC). The Raman spectrum of the virgin glassy carbon shows the disorder (D) and graphitic (G) peaks which characterize disordered carbon materials. Merging of these two peaks was observed when the virgin sample was implanted with strontium ions. Merging of these peaks is due to damage caused by the implantation of strontium. The Raman spectrum recorded after heat treatment showed that only some of the damage due to implantation was annealed out. Annealing at 20000C for 5 hours resulted in a Raman spectrum very similar to that of virgin glassy carbon indicating that the damage due to the ion implantation was annealed out. SEM showed large differences in the surface topography of the polished glassy carbon surfaces and those of as-implanted samples. Annealing did not significantly change the surface microstructure of the implanted samples. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Physics / unrestricted