Theses, Dissertations and Student Research Papers (Chemistry)

The atmospheric chemistry of particulate-bound polycyclic aromatic hydrocarbons : concentration, prediction, laboratory studies, and mutagenicity

2013-06-11T18:20:27Z

The atmospheric chemistry of particulate-bound polycyclic aromatic hydrocarbons : concentration, prediction, laboratory studies, and mutagenicity Jariyasopit, Narumol The trans-Pacific atmospheric transport of particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) to remote sites in western North America has been well documented and has triggered research questions regarding to atmospheric transformation of PM-bound PAHs and the potential impacts on human health from their inhalation exposure. In this dissertation, field measurements, theoretical studies, laboratory experiments, and mutagenicity studies were used to begin the address the questions as to whether PM-bound PAHs undergo atmospheric transformation into mutagenic nitro-PAHs (NPAHs) during trans-Pacific atmospheric transport. PM extracts were tested in the Salmonella mutagenicity assay, using Salmonella typhimurium strain TA98 (with and without metabolic activation), to determine the mutagenic activities in relation to the chemical composition of the extracts. The sampling of atmospheric PM with diameter < 2.5 μm (PM₂.₅) before, during, and after the Olympic Games 2008 in Beijing provided some insights into the concentrations, chemical composition, photochemistry, and mutagenicity at the source of emission. The PAH, NPAH and OPAH composition of the PM₂.₅ was similar throughout the sampling periods, which included the period when a wide range of combustion sources were controlled. In addition, it showed that PAHs were associated with both local and regional emissions, while the NPAH and OPAH concentrations were only correlated with the NO concentrations, indicating that the NPAH and OPAH were primarily associated with local emissions. The characteristic NPAH ratios suggested a predominance of photochemical formation of NPAHs through OH radical-initiated reactions in the atmosphere. Subsequently, the heterogeneous reactions of PAHs bound to Beijing ambient PM with various oxidants, including NO₃/N₂O₅, OH radical and O₃, were studied using an environmental reaction chamber under simulated trans-Pacific transport conditions. In addition, PM collected from Riverside, CA was simultaneously exposed along with the Beijing PM in order to allow us to compare the reactivity between two different sites. In general, O₃ was most effective in degrading PM-bound PAHs with more than five rings, except for benzo[a]pyrene which was degraded by O₃ and NO₃/N₂O₅ equally well. However, the NPAHs were most effectively formed during the NO₃/N₂O₅ exposure. The reactivity of the PM could be explained by the degree to which the PM had been photochemically aged because the accumulation of degradation products on the surface of PM appeared to inhibit further atmospheric degradation of parent PAHs. For the NO₃/N₂O₅ exposure, the increase in direct-acting mutagenicity was associated with the formation of mutagenic NPAHs. Additional laboratory experiments were carried out in order to identify NPAH products of 5- to 6-ring PAHs through the heterogeneous reactions of surface-bound PAHs with NO₂, NO₃/N₂O₅, O₃, and OH radicals. Five PAHs, benzo[a]pyrene-d₁₂, benzo[k]fluoranthene-d₁₂, benzo[g,h,i]perylene-d₁₂, dibenzo(a,i)pyrene-d₁₄, and dibenzo[a,l]pyrene, were spiked onto quartz fiber filters and exposed in the chamber. Some of the identified NPAH products have not yet been measured in the environment. In parallel to the laboratory experiments, a theoretical study was conducted to assist in predicting the formation of NPAH isomers based on the gas-phase OH radical-initiated reaction. This study has shown that NO₂ and NO₃/N₂O₅ were effective oxidizing agents in transforming PAHs deposited on filters to NPAHs, under these experimental conditions. The lighter of the PAHs studied, including benzo[a]pyrene-d₁₂, benzo[k]fluoranthene-d₁₂ and benzo[ghi]perylene-d₁₂, yielded more than one mono-nitro isomer product, whereas dibenzo[a,l]pyrene and dibenzo[a,i]pyrene-d₁₄ resulted in the formation of only one mono-nitro isomer product. The direct-acting mutagenicity increased the most after NO₃/N₂O₅ exposure, particularly for benzo[k]fluoranthene-d₁₂ in which dinitro PAHs were observed. Graduation date: 2013

The distribution of organic bases in reverse phase liquid chromatography : a study of mechanisms

2013-04-18T20:03:19Z

The distribution of organic bases in reverse phase liquid chromatography : a study of mechanisms Jayasinghe, Dudley Shelton The distribution of hydrophobic ionogenic organic compounds (HIOC's) between aqueous and nonaqueous phases has been investigated. The HIOC's are aniline and methyl substituted anilines. The aqueous phases are methanol-water mixed solvents with varying pH and ionic strength. The nonaqueous phases are silica and alkyl derivatized silica with ethyl- (C-2), octyl- (C-8), and octadecyl- (C-18) silanes. A gas-liquid equilibration method has been developed to determine the Henry's law constants and the activity coefficients of methyl anilines in methanol-water mixed solvents. The logarithm of the Henry's law constants vary quadratically with the volume fraction of methanol. The chromatographic study has been performed to investigate the effect of three mobile phase factors, fraction of methanol, pH, and ionic strength, on the retention of methyl anilines on different stationary phases. The logarithm of mass distribution ratios, log k's, of methyl anilines vary linearly with the volume fraction of methanol. The ratios of H / k' of methyl anilines increase with increase in methanol in the mobile phase, indicating an increase in the activity coefficients in the stationary phases. This observation is found to be true for different methyl anilines in different stationary phases. A partition model is presented to describe the effect of pH and ionic strength on the retention of HIOC's in the mobile phase. The variation in log k' among neutral and ionic methyl anilines can be explained by linear free energy relationships. Equations are established to predict retention of neutral or ionized methyl anilines from their octanol-water partition coefficients at any methanol content in the mobile phase. Acid dissociation constants of methyl anilines determined from the dependence of log k' on pH are in close agrement with those determined by potentiometric titrations. The effect of ionic strength on the retention of both neutral and ionic species of methyl anilines is negligible. That is, the contribution from electrostatic energy and salting out effect are not significant. The chromatographic study is extended to study the retention of methyl anilines on silica as a function of pH and methanol at a constant ionic strength. The dependence of retention on pH is qualitatively interpreted from an ion exchange reaction between the dissociated silanol groups in the surface and the ionized methyl anilines. The effect of methanol on the retention of methyl anilines and of pyridine on silica is described by a quadratic relationship between the log k' and volume fraction of methanol. Graduation date: 1990

The characterization and simplex optimization of a variable-diameter, multielectrode, direct current plasma for atomic emission spectroscopy

2013-04-12T17:14:52Z

The characterization and simplex optimization of a variable-diameter, multielectrode, direct current plasma for atomic emission spectroscopy McGuire, Joseph Graduation date: 1990

Development of automated flow injection apparatus and a novel flow cell for chemi- and bioluminescence determinations

2013-04-12T16:18:52Z

Development of automated flow injection apparatus and a novel flow cell for chemi- and bioluminescence determinations Gander, Stuart C. A practical and versatile instrument has been developed both to optimize the chemistry of bio- and chemiluminescence reactions and to measure ultra-trace quantities of associated analytes. The instrument consists of a pneumatic flow injection system linked to a detection cell and a signal processing and readout system. The disk-like cell is defined by a pair of transparent polycarbonate plates and an "0-ring" seal. The lower plate is fitted with a reflective surface. Relative to conventional cells, this design affords a high light collection efficiency due to the large volume element viewed by an end-on photomultiplier detector. Rapid mixing of reagents within the cell is brought about by injection through concentric ports of a commercial burner assembly at a point immediately below the detector. The signal processing and readout system is interfaced to an IBM compatible personal computer and appropriate software was written to automate the instrument and to acquire, store and manipulate luminescence data. With this instrumentation, the chemistry of marine bacteria biolumin-escence was optimized for the determination of cis-11-hexadecenal and, ostensibly, for both the quantification of aldehyde insect pheromones and potential use in the control of insect pests. With the optimized conditions, cis- 11-hexadecenal was determined to 7 fmol. This value is more than an order of magnitude lower than detection limits for aldehyde pheromones reported in the literature. In this research, the less ideal substrates undecanal and heptanal were determined to 570 fmol and 65 pmol, respectively. Marine bacteria bioluminescence was used to quantify several epoxide analytes derivatized to aldehydes. 1,2-epoxyhexadecane and 1,2- epoxytetradecane were determined to 55 and 51 fmol, respectively. 1,2- epoxyoctane and cis-7,8-epoxy-2-methyloctadecane were determined to 100 and 3 pmol, respectively. The latter compound is the sex pheromone of the gypsy moth (Lymantria dispar), a well-known and serious agricultural pest. Epoxides have not been quantified previously with either chemi- or bioluminescence. The instrument was modified for use with corrosive solutions and for possible interfacing with a high performance liquid chromatograph. Lophine chemiluminescence was optimized for the analysis of Cr(VI) samples. With the optimized conditions, aqueous solutions of Cr(VI) were determined to 50 μg /L. A plausible explanation is offered for the dependence of lophine chemiluminescence on the concentration of the chromium species. Graduation date: 1991