published_or_final_version / abstract / toc / Chemistry / Doctoral / Doctor of Philosophy

New approaches to the analysis of trace metal concentrations in seawater have the potential to advance the field of oceanography and provide a more comprehensive understanding of the marine biogeochemical cycles of trace metals and the processes regulating these cycles. Traditional oceanographic methods of trace metal analysis were developed several decades ago using benchtop liquid-liquid extraction (Danielson et al., 1978; Kinrade and Van Loon, 1974; Miller and Bruland, 1994; Moffett and Zika, 1987). More modern techniques utilize flow based solid phase extraction to eliminate the high ionic strength matrix to determine dissolved concentrations with great accuracy and precision but do not allow for the determination of metal speciation in solution (Wells and Bruland, 1998). The method developed here measures oceanographically relevant concentrations of copper (Cu) in seawater via chemiluminescence (Marshall et al., 2003 and Coale et al., 1992) and micro-molar levels of silver (Ag) colorimetrically after automated liquid-liquid extraction. The Zone Fluidics (Marshall et al., 2003) analyzer for trace Cu determined SAFe D2 standard seawater (www.geotraces.org) to be 1.77 nM Cu comparable to the expected consensus value. The method was used to determine dissolved Cu depth profiles for major stations along the Line P Time-series transect (48N 125W - 50N 145W) in the Pacific Ocean during February 2011. This method consumes less than 200 µL of sample and reagents and is performed in less than 3 minutes making it suitable for ship or lab based analysis. / Graduate / 0485 / 0425 / cschwang11@gmail.com

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 195-212) Also available in print.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 58-62). Also available on the World Wide Web.

Do interesse em espécies eletronicamente excitadas geradas por sistemas luminescentes químicos e biológicos, nasceu o interesse dos químicos pelos dioxetanos, seu comportamento e suas propriedades. Propostos como intermediários de tais reações, estes compostos (peróxidos cíclicos de anel tetratômico) sofrem clivagem térmica unimolecular com produção de dois fragmentos carbonílicos, um deles no estado eletronicamente excitado. Em geral, dioxetanos substituídos por grupos alquílicos e arílicos levam a altos rendimentos de estados triplete. Propôs-se, então, reinvestigar a termólise do tetrametildioxetano (TMD) em meio aquoso e utilizar esta fonte de acetona triplete como modelo químico, para o sistema enzimático de produção de acetona triplete (oxidação aeróbica do isobutanal (IBAL)/peroxidase (HRP)), em estudos de supressão e transferência de energia. O TMD tem sido preparado e cristalizado rotineiramente em nosso laboratório, pelo método de Kopecky. Os parâmetros de ativação de termólise (estabilidade térmica e rendimentos de quimiexcitação dos produtos) foram reestudados em solventes aromáticos (benzeno e tolueno), cicloalifáticos (ciclohexano e decalina), próticos (água) e apróticos (acetonitrila e CCl4).Concluiu-se que: (i) a estabilidade do TMD não é afetada pela natureza do solvente (Ea ~ 27,0 kcal mol-1); (ii) a eficiência global de transferência de energia triplete (acetona) → singlete (9,10-dibromoantraceno) nos solventes não aromáticos é praticamente constante (ΦTS ~ 10 %); (iii) em solventes aromáticos onde o doador excitado é na verdade um \"exciplex\" acetona-solvente, ΦTS ~ 30 %. A relação entre os rendimentos de quimiexcitação de triplete e singlete (3Φ /1Φ) em água foi determinada como sendo da ordem de 1x103, que concorda com valores determinados em tolueno e benzeno (7x102 e 8x102, respectivamente). Nos estudos em meio aquoso, o DBAS e o DPAS foram utilizados para monitorar a presença de acetona triplete e singlete, formada química, fotofísica ou enzimaticamente. Ambos foram sintetizados em nosso laboratório e suas propriedades fotofísicas, determinadas em água deionizada a 20°C. Através da medida de fluorescência do DBAS excitado por transferência de energia a partir de acetona triplete, determinou-se a vida média de acetona triplete em meio aquoso aerado e deaerado (τaer ~ 2 µs e τN2 ~ 10 a 20 µs). Seis classes de interceptadores de acetona triplete, gerada na termólise de TMD, foram investigadas em tampão aquoso a 35°C: dienos (ácido sórbico e acrilonitrila), pigmentos xantênicos, riboflavina, tirosina e derivados 3,5-dihalogenados, indol e derivados indólicos, e uma série de quinonas. Em geral, os valores das constantes de supressão de acetona triplete produzida diretamente no seio da solução, a partir de TMD, estão pelo menos uma ordem de grandeza abaixo dos valores correspondentes para acetona triplete produzida enzimaticamente. Estes resultados são consistentes com a hipótese de que acetona triplete gerada dentro da enzima tem vida média mais longa, pois se encontraria parcialmente \"protegida\" da ação supressora de O2. Outros argumentos podem, entretanto, ser igualmente satisfatórios. Parece claro que os supressares indólicos (IP ~ 8 eV) e ácido sórbico exercem sua ação através da formação de complexos de transferência de carga, tirosina e corantes xantênicos (IP ~ 7 eV) por um mecanismo de transferência de elétrons e riboflavina por mecanismo tipo Förster. As quinonas, cuja afinidade eletrônica é bastante alta (IP ~ 10-11 eV), suprimem acetona triplete por um mecanismo controlado por difusão; com estes compostos, o limite superior do esperado para um processo puramente colisional seria atingido (kq ~ 1 a 2x1010 M-1s- 1, em água a 35°C). De fato, derivados metilados de p-benzoquinona e naftoquinona suprimem acetona triplete com velocidade mais baixa, enquanto que em solvente mais viscoso (decalina, em relação a n-hexano), kq também é mais lenta. Por outro lado, observou-se um marcante \"efeito de átomo pesado\" na eficiência de transferência de energia triplete (acetona) → singlete (corante xantênico): ΦTS para fluoresceína, eosina e Rose Bengala na proporção 1:15:320. A oxidação da clorpromazina (CPZ) por reação com o TMD foi estudada em meio aquoso e meio tamponado e verificou-se que esta independe da formação de espécies excitadas, apesar da CPZ apresentar-se como eficiente supressor de acetona triplete. Espectros de RMN1H mostraram que a reaçao entre CPZ e TMD gera a clorpromazina-5-óxido (sulfóxido; CPZO) e o óxido de tetrametiletileno (o epóxido correspondente ao TMD). Estudos de espectroscopia U.V. e de cromatografia gasosa indicam que a estequiometria da reação TMD/CPZ é 1:1 e que a presença de competidores de supressão de acetona triplete não altera a velocidade da reação nem a estequiometria da mesma. Em vista destes resultados, reestudou-se a oxidação de CPZ pelo sistema do IBAL/HRP/O2, estudo feito inicialmente por DURÁN e colaboradores, no qual os autores propõem que a oxidação de CPZ é resultante de transferência de energia de excitação da acetona triplete gerada enzimaticarnente. Usando métodos inexplorados até então, verificamos a possibilidade de esta oxidação ocorrer por reação direta entre CPZ e os radicais de HRP formados durante a oxidação do isobutanal, sem a intervenção da acetona triplete. Outro estudo parelelo a este, foi feito visando determinar parâmetros cinéticos e termodinâmicos em dioxetanos com diferentes tipos de hidrogênios em posição γ do anel. Este estudo visava determinar de que maneira a interação oxigênio do anel-hidrogênio gama influia em tais parâmetros. Sintetizou-se uma série de 3-metil-3-alquildioxetanos (alquil = n-propil, n-butil e neopentil) e determinamos os seus parâmetros de ativação de termólise (Ea, ΔS≠, 3Φ e 1Φ). Constatamos que não há diferença significativa entre estes dioxetanos, sendo assim, a interação hidrogênio gama-oxigênio do anel é inexpressiva. Porém, quando comparados com outros dioxetanos da mesma série, onde alquil = etil, isopropil e terc-butil (estudo em conjunto com outros pesquisadores) nota-se urna expressiva mudança na Ea a medida que aumenta o número de grupos rnetila na posição α, indicando um efeito estérico do tipo 3,3. / The interest in eletronically excited species generated by chemical and biological systems give rise to at interest in dioxetanes, their behavior and their properties. These coumpounds (cyclic four-membered ring), which have been proposed as intermediates in such reactions, undergo unimolecular thermal cleavage yielding two carbonyl fragments, one of which is tipically formed electronically excited. In general, alkyl and aryl substitued dioxetanes give high yields of triplet states. In the present work, the thermolyses of tetramethyldioxetane (TMD) was reinvestigated in agueous medium. This source of triplet acetone was then employed in quenching and energy transfer studies as a chemical model for the enzymatic systems which produces triplet acetone I aerobic oxidations of isobutanal (IBAL) catalysed by horseradish peroxidase (HRP) I. TMD was prepared and crystalised normally in our laboratory using Kopecky\'s method. Thermal activation parameters (thermal stability and chemiexcitation quantum yields) have been determined in several types of solvents, including aromatics (benzene and toluene), cycloaliphatics (cyclohexene and decalin), protic (water) and aprotic (acetonitrile and carbon tetrachloride) .We conclude that: (i) TMD stability is not affected by the nature of the solvente (Ea ~ 27,0 kcal/mol), (ii) the overall energy transfer efficiency 3Ac* → 1DBAS* is practically constant (ΦTS ~ 10%) in non-aromatic solventsi (iii) in aromatic solvents, where the excited donor is an acetone-solvent \"exciplex\", ΦTS ~ 30%. The ratio of triplet and singlet chemiexcitation yields (3Φ /1Φ) in water was deterrnined to be 1x103. This value is in good agreement with these determined in toluene and benzene (7x102 and 8x102, respectivelly). In studies in aqueous medium, DBAS and DPAS were used as probes to monitor the production of triplet and singlet acetone formed chemically, photophysically or enzymatically. Both probes were prepared in our laboratory and their photophysical properties deterrnined in deionized water at 20°C. The lifetime of triplet acetone in aerated and deaerated aqueous media was deterrnined on the basis of the cherniluminescence intensity of DBAS excited by energy transfer (τaer ~ 2 µs e τN2 ~ 10 a 20 µs). Six classes of quenchers were investigated in aqueous buffer at 35°C: dienes (sorbic acid and acrylonitrile), xanthene dyes, tyrosine and its 3,5-dihalogenoderivatives, indole and indolic derivatives, riboflavin and a serie of quinones. In general, rate constants for quenching of triplet acetone produced free in solution via TMD thermolyses are one order of magnitude lower than those for quenching of enzymatically generated triplet acetone. These results are in line with the hypothesis of a longer lifetime of the triplet acetone generated within the enzyme due a parcial \"protection\" for O2 quenching. It seerns clear that the indolic coumpounds (IP ~ 8 eV) and sorbic acid quench triplet acetone through the forrnation of a charge-transfer complex, tyrosine ans xanthene dyes (IP ~ 7 eV) by an electron-transfer mechanism and riboflavin by a Förster type mechanism. The quinones, which have high electronic affinities (IP ~ 10- 11 eV) , quench triplet acetone by a diffusion controlled process (kq ˜ 1 to 2x1010 M-1s-1 in water at 35°C). Methyl derivatives of p-benzoquinone and naphtoquinone quench triplet acetone at a slower rate; kq is also lower in a more viscous solvent (decalin versus n-hexane). On the other hand, the results indicate a strong \"heavy atom effect\" on the energy transfer efficiency from triplet acetone to singlet xanthene dye: ΦTS for fluorescein, eosin and Rose Bengal in the ratio 1:15:320. The chlorpromazine (CPZ) oxidation by reaction with TMD was studied in aqueous and buffered media. This reaction does not depend on the production of excited species, even though CPZ proved to be an efficient trip1et acetone quencher. The NMR1H spectra showed that chlorpromazine-5-oxide and tetrarnethylene oxide are the products of the reaction between CPZ and TMD. UV spectroscopic and gas chromatographic studies indicated a 1:1 stoichiometry for the TMD/CPZ reaction and no competition between this reaction and triplet acetone quenching by indole or sorbate. In view of these results, we reinvestigated the oxidation of CPZ by the IBAL/HRP/02 system, a reaction which has been suggested to occur via energy transfer from triplet acetone to CPZ in an earlier study. Using methods developed since the earlier study, we verified that this reaction in fact occurs via direct reaction between CPZ and HRP radicals produced during IBAL oxidation, without the intervention of triplet acetone. In another parallel study, we determined kinetic and thermodinamic parameters of a series of dioxetanes with different types of γ hydrogens in order to examine how the interaction between oxygen and the γ hydrogens might influence these parameters. Thus, a series of 3-methyl-3-alkyldioxetanes (alkyl = n-propyl, n-butyl and neopentyl) was sintesized and their thermal activation parameters (Ea, ΔS≠, 3Φ and 1Φ) determined. The results indicated that there are no significant differences among these dioxetanes; consequently the oxygen-γ hydrogen interaction is relativelly unimportant. However, when compared with other dioxetanes of similar structure (alkyl=ethyl, isopropyl and terc-butyl; joint study done with other researchers), there is a significant change in Ea upon increasing the number of rnethyl groups at the α position, pointing to a steric effect of the 3,3 type.

A fast response method for the determination of temperature and equivalence ratio has been developed for turbulent premixed flames. This method utilizes chemiluminescent signals to make correlations with flame temperature and equivalence ratio. Emissions from two radical groups are used for the correlations: an OH system at 309 nm and a CH system at 431 nm. The experimental apparatus consists of a turbulent burner, an optical system (lenses, monochromator, and photomultiplier tube), and a data collection system (digital oscilloscope and computer). An optical system using fiber optics and band pass interference filters was also investigated. The spectra of turbulent, premixed methane flames of known stoichiometry were recorded. A high temperature Pt-Pt10%Rh thermocouple was used to establish flame temperature. The ratio of signal width to signal height of the OH spectra was used to correlate flame temperature. The ratio of OH to CH signal heights was used to correlate equivalence ratio. Turbulent correlations were compared to laminar correlations developed in previous studies. The effect of increasing turbulence on correlations was investigated. Applications for this technology and recommendations for future work are discussed. / Master of Science

There are two critical research needs for the study of hydrocarbon combustion in high speed flows: 1) combustion diagnostics with adequate temporal and spatial resolution, and 2) mathematical techniques that can extract key information from large datasets. The goal of this work is to address these needs, respectively, by the use of high speed and multi-perspective chemiluminescence and advanced mathematical algorithms. To obtain the measurements, this work explored the application of high speed chemiluminescence diagnostics and the use of fiber-based endoscopes (FBEs) for non-intrusive and multi-perspective chemiluminescence imaging up to 20 kHz. Non-intrusive and full-field imaging measurements provide a wealth of information for model validation and design optimization of propulsion systems. However, it is challenging to obtain such measurements due to various implementation difficulties such as optical access, thermal management, and equipment cost. This work therefore explores the application of FBEs for non-intrusive imaging to supersonic propulsion systems. The FBEs used in this work are demonstrated to overcome many of the aforementioned difficulties and provided datasets from multiple angular positions up to 20 kHz in a supersonic combustor. The combustor operated on ethylene fuel at Mach 2 with an inlet stagnation temperature and pressure of approximately 640 degrees Fahrenheit and 70 psia, respectively. The imaging measurements were obtained from eight perspectives simultaneously, providing full-field datasets under such flow conditions for the first time, allowing the possibility of inferring multi-dimensional measurements. Due to the high speed and multi-perspective nature, such new diagnostic capability generates a large volume of data and calls for analysis algorithms that can process the data and extract key physics effectively. To extract the key combustion dynamics from the measurements, three mathematical methods were investigated in this work: Fourier analysis, proper orthogonal decomposition (POD), and wavelet analysis (WA). These algorithms were first demonstrated and tested on imaging measurements obtained from one perspective in a sub-sonic combustor (up to Mach 0.2). The results show that these algorithms are effective in extracting the key physics from large datasets, including the characteristic frequencies of flow—flame interactions especially during transient processes such as lean blow off and ignition. After these relatively simple tests and demonstrations, these algorithms were applied to process the measurements obtained from multi-perspective in the supersonic combustor. compared to past analyses (which have been limited to data obtained from one perspective only), the availability of data at multiple perspective provide further insights into the flame and flow structures in high speed flows. In summary, this work shows that high speed chemiluminescence is a simple yet powerful combustion diagnostic. Especially when combined with FBEs and the analyses algorithms described in this work, such diagnostics provide full-field imaging at high repetition rate in challenging flows. Based on such measurements, a wealth of information can be obtained from proper analysis algorithms, including characteristic frequency, dominating flame modes, and even multi-dimensional flame and flow structures. / Ph. D.

Thermoacoustic instabilities in gas turbine operation arise due to unsteady fluctuations in heat release coupled with acoustic oscillations, often caused by varying equivalence ratio perturbations within the flame field. These instabilities can cause irreparable damage to critical turbine components, requiring an understanding of the spatial/temporal variations in equivalence ratio values to predict flame response. The technique of computed tomography for flame chemiluminescence emissions allows for 3D spatially resolved flame measurements to be acquired using a series of integral projections (camera images). High resolution tomography reconstructions require a selection of projection angles around the flame, while captured chemiluminescence of radical species intensity fields can be used to determine local fuel-air ratios. In this work, a tomographic reconstruction algorithm program was developed and utilized to reconstruct the intensity fields of CH* and OH*, and these reconstructions were used to quantify local equivalence ratios in an acoustically forced flame. A known phantom function was used to verify and validate the tomography algorithm, while convergence was determined by subsequent monitoring of selected iterative criteria. A documented method of camera calibration was also reproduced and presented here, with suggestions provided for future calibration improvement. Results are shown to highlight fluctuating equivalence ratio trends while illustrating the effectiveness of the developed tomography technique, providing a firm foundation for future study regarding heat release phenomena. / Master of Science / Acoustic sound amplification occurs in the combustion chamber of a gas turbine due to the machine ramping up in operation. These loud sound oscillations continue to grow larger and can damage the turbine machinery and even threaten the safety of the operator. Because of this, many researchers have attempted to understand and predict this behavior in hopes of ending them altogether. One method of studying these sound amplifications is looking at behaviors in the turbine combustion flame so as to potentially shed light on how these large disturbances form and accumulate. Both heat release rate (the steady release of energy in the form of heat from a combustion flame) and equivalence ratio (the mass ratio of fuel to air burned in a combustion process) have proven viable in illustrating oscillatory flame behavior, and can be visualized using chemiluminescence imaging paired with computed tomography. Chemiluminescence imaging is used to obtain intensity fields of species from high resolution camera imaging, while computed tomography techniques are capable of reconstructing these images into a three-dimensional volume to represent and visualize the combustion flame. These techniques have been shown to function effectively in previous literature and were further implemented in this work. A known calibration technique from previous work was carried out along with reconstructing a defined phantom function to show the functionality of the developed tomography algorithm. Results illustrate the effectiveness of the tomographic reconstruction technique and highlight the amplified acoustic behavior of a combustion flame in a high noise environment.

A fast response method for detection of ignition and extinction of liquid spray flames has been improved. Also, a method of determining fuel-to-air ratios and temperatures of pre-mixed, gaseous flames has been developed. Both methods utilize chemiluminescent signals from an OH system centered at 309 nm and a CH system centered at 431 nm. The ignition and extinction method was improved by replacing an optical system composed of lenses and a monochromator by a system composed of a fiber optic cable and band pass interference filters. The use of a solid-state photodiode instead of a photomultiplier tube was investigated. Transient histories of the OH and CH signals were recorded by performing light-off ignition and intermittent ignition flame tests. These signal histories were compared to histories obtained using the original apparatus. The fuel-to-air ratio and temperature detection method was investigated by recording the spectra of laminar, pre-mixed methane flames of known stoichiometry with a lens, monochromator, and photomultiplier tube set-up and measuring the flame temperatures with a high-temperature Pt-10%Rh thermocouple. Various combinations of signal characteristics were found to be functions of fuel-to-air ratio and temperature. Optimum signals for monitoring with a detector were determined. Recommendations for future work in this area are discussed. / Master of Science

Combustion monitoring in internal combustion engine or burners is a difficult task due to the harsh environment for any sensor, therefore optical diagnostics are very attractive for these types of application. Chemiluminescence measurement is one of the most common and most promising ways of implementing optical diagnostics in combustion monitoring applications because the measured signal, emitted naturally with combustion, has potential to be an indirect measure of combustion relevant parameters, such as the equivalence ratio and heat release rate. In hydrocarbon combustion, the most common chemiluminescence emitters are OH*, CH*, C₂* and CO₂*. This thesis focuses on the measurement of OH* and CH* chemiluminescence, whose sensitivities are affected by temperature, pressure, equivalence ratio and stretch rate. To measure OH* and CH* chemiluminescence, an existing constant volume combustion vessel has been refurbished, along with the sub-systems for fuel delivery, ignition, LabView control, data acquisition, and optical detection using a pair of photo-multiplier tubes (PMTs), interference filters and a series of apertures. Modelling accurately the optical setup is essential for the CH* and OH* chemiluminescence measurements in the combustion bomb. To achieve this goal, a narrow field of view system has been selected as it enables the elimination of photons scattered from the internal surfaces. A calibration of the PMTs converts the measurements into the absolute OH* and CH* chemiluminescence in terms of watt. Measurements from a combustion bomb are versatile and accurate since it determines the OH* and CH* chemiluminescence as a function of temperature and pressure from a single experiment. The calculation of the normalised OH* and CH* chemiluminescence (against mass burned rate) was based on a multi-zone combustion model and measured pressure record from the vessel. NIICS (Normalised Intensity Integrated Calculation System) has been created to fetch data from the multi-zone model, the optical model, and experimental measurements, to match them up by interpolation and to normalise the OH* and CH* chemiluminescence. NIICS also allows the user to select data uncorrupted by the noise and heat transfer. The chosen data (in this case, CH*/OH* chemiluminescence ratio) have been fitted using a multi-variate fitting and correlation analysis. This formulation can be used to indicate the local equivalence ratio from premixed methane / air and iso-octane / air flames over the local pressure range 0.5 – 20 bar, the unburned gas temperature range 450 – 600 K, and equivalence ratio range 0.8 – 1.1. The chemical-kinetic mechanisms of the absolute OH* and CH* chemiluminescence have been investigated by studying the influence of the equivalence ratio, unburned gas temperature, and local pressure. It should be pointed out that two confounding observations occur, i.e. a discontinuity in the chemiluminescence along the isentropes, and chemiluminescence continuing after the end of combustion. This led to the further spectroscopic analysis. This study concluded with spectroscopic measurements using an Ocean Optics spectrometer and a Princeton ICCD spectrometer. It was found that the broadband CO₂* is responsible for the two disconcerting observations. In addition, CH* chemiluminescence has been shown to be very faint from premixed laminar methane / air flames; hence the CH*/OH* formula in essence quantifies the CO₂*/OH* ratio as a function of pressure, temperature, and equivalence ratio. The ‘CH* chemiluminescence’ can characterise the background CO₂*, so as to provide a practical way to probe the feasibility of absolute OH* as an indicator of combustion relevant parameters in the future.