Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 148-155). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 165-172). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 165-172). Also available on the Internet.

This study has two aspects. One concerns the development of a sensitive differential pulse polarographic (DPP) method and its use to conduct a preliminary study of natural waters to detect the presence of nitrosoamines, and the second, where the study was carried out in greater detail, is the investigation of the kinetics of reduction of N-nitrosodimethylamine (NDMA) in aqueous solution. An optimization study was first conducted to identify the conditions that give the greatest sensitivity. Conditions investigated were different supporting electrolytes and solvent mixtures. Supporting electrolytes used were 0.10 M solutions of acids, bases and salts, and the solvent mixtures studied were ethanol/water mixtures. The effect of various supporting electrolytes and various ethanol/water mixtures on peak current was studied in order to select the conditions that give the greatest sensitivity for the determination of nitrosoamine concentrations. The lowest nitrosoamine concentration that can be detected in a solution (limit of detection) was determined. The optimum supporting electrolytes for N-nitrosoamines and the C-nitrosoamine were respectively found to be 0.10 M H2S04 and 0.10 M NaOH. Aqueous solutions were also found to give greater sensitivity than ethanol/water mixtures. The presence of nitrosoamines in some natural water samples was then checked using differential pulse polarography (DPP).Concentrations of nitrosoamines in these water samples were determined using the optimum conditions. The analyte analytes studied were 4-nitroso-N,N-dimethylaniline (4NDMA); Nnitrosodibutylamine (NDBA),N-nitrosodi-n-propylamine (NDPA) and N-nitrosodiphenylamine (NDPhA). All four nitrosoamines were detected in some of the selected natural water samples . The kinetics of the electrochemical reduction of NDMA was studied using controlled potential coulometry, linear scan voltammetry (LSV) and cyclic voltammetry (CV). Controlled potential coulometry was first used to determine the number of electrons transferred (n) in the reduction reaction. Two moles of electrons were found to be required for the reduction of one mole of NDMA solution, at a stationary mercury drop electrode (SMDE). The major product obtained, identified by UVNIS spectroscopy, was dimethylamine (DMA). / Ph.D. (Chemistry) North-West University, Mafikeng Campus, 2005

published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

Graduation date: 1993

The rejections of selected N-nitrosamines by commonly used high-pressure nanofiltration (NF) and reverse osmosis (RO) membranes were quantitatively evaluated using a bench-scale cross-flow filtration apparatus. The selected nitrosamines included N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA) and N-nitrosodiphenylamine (NDPHA). Nitrosamine rejections were evaluated under steady state at elevated feed concentrations, since NDMA rejections were found to be consistent with feed concentrations over three orders of magnitude. The steady-state nitrosamine rejections by NF membranes varied significantly, from 9 to 75%, depending on nitrosamine compounds and tested membranes. For hydrophilic compounds, rejections increased with increasing molecular weight. The nitrosamine rejections by brackish RO membranes reached as high as 97% for higher molecular weight nitrosamines. However, for low molecular weight nitrosamines such as NDMA, rejections as low as 54% were observed. This low level of rejections was attributed to diffusive solute transport being more effective than convective transport. Physicochemical properties such as molecular weight and aqueous diffusivity showed reasonable correlations with nitrosamine permeability constants.

Thesis (M. Phil.)--University of Hong Kong, 1987.

published_or_final_version / Biochemistry / Master / Master of Philosophy

N-Nitrosamines are an emerging group of disinfection byproducts characterized by high carcinogenic risks at ng/L levels and by their frequent detection in water and wastewater treatment systems in the U.S. and other parts of the world. The overall goal of this research is to achieve a better understanding of the roles of common nitrosamine precursors in leading to N-nitrosamine formation in water and wastewater treatment systems. The specific objectives of this research are: (a) To probe the mechanisms of nitrosamine formation from commonly employed water treatment polymers, particularly polyDADMACs, during ozonation, (b) To evaluate the role of dithiocarbamate compounds as nitrosamine precursors in reaction with common water disinfection oxidants, and (c) To investigate the potential enhancement effect of activated carbons (AC) to promote transformation of amines to nitrosamines and identify the involved reaction mechanism. Results of this research show that, upon ozonation, polyDADMACs may yield N-nitrosodimethylamine (NDMA) at levels up to two orders of magnitude higher than current advisory guidelines for NDMA. Radical pathways may be responsible for the degradation of the quaternary ammonium ring groups in polyDADMACs to release of dimethylamine (DMA). Detection of significant amounts of nitrite after ozonation of polyDADMACs and DMA suggests the potential role of nitrosation pathway in NDMA formation. Study results also reveal dithiocarbamates as potent nitrosamine precursors with significant nitrosamine yields upon ozonation and monochloramination. Identification and quantification of reaction products suggest nitrosation and chlorinated-UDMH oxidation as primary reaction mechanisms in nitrosamine formation from ozonation and monochloramination of dithiocarbamates compounds, respectively. This research also demonstrates that many commercial AC materials may catalyze transformation of secondary amines to yield trace levels of N-nitrosamines under ambient aerobic conditions. This is a novel discovery with far-reaching implications because of the widespread usage of AC materials in numerous analytical and environmental applications. The study results show that the properties of AC materials and reaction conditions play a crucial role in the catalyzed nitrosamine formation and should be carefully selected to minimize analytical errors and undesirable nitrosamine formation in water samples. Overall, the mechanistic information obtained in this research will be useful for the water industry and research communities to develop more effective strategies to control undesirable nitrosamine formation in water and wastewater treatment systems and thus better protect the public health.