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A method has been developed that uses uranium hexafluoride as the internal standard to quantitatively determine trace impurities in the uranium hexafluoride using relative response factors. A computer program was written to control the mass spectrometer and determine the concentrations of target impurities present. Overlapping spectra are deconvoluted using the Gauss-Seidel iterative method. The composition of the sample is determined by comparing the peak height ratios of the target impurities to the internal standard. Measurement parameters are easily modified using the menu driven program. A flexible database allows the list of target impurities to be extended to accommodate any changes in analytical requirements. The method has been adapted for automatic on-line measurements. The technique was evaluated by analysing a number of carefully prepared standards. Nine target impurities were studied which ranged in concentration from parts per million to percentages. An overall precision of fifteen percent was obtained. / Dissertation (MSc)--University of Pretoria, 1993. / gm2013 / Chemistry / unrestricted

Functional data analysis is a eld in statistics that analyzes data which are dependent on time or space and from which inference can be conducted. Functional data analysis methods can estimate residuals from functional regression models that in turn require robust univariate density estimators for error density estimation. The accurate estimation of the error density from the residuals allows evaluation of the performance of functional regression estimation. Kernel density estimation using maximum likelihood cross-validation and Bayesian bandwidth selection techniques with a Gaussian kernel are reproduced and compared to least-squares cross-validation and plug-in bandwidth selection methods with an Epanechnikov kernel. For simulated data, Bayesian bandwidth selection methods for kernel density estimation are shown to give the minimum mean expected square error for estimating the error density, but are computationally ine cient and may not be adequately robust for real data. The (bounded) Epanechnikov kernel function is shown to give similar results as the Gaussian kernel function for error density estimation after functional regression. When the functional regression model is applied to a chemometric data set, the local least-squares cross-validation method, used to select the bandwidth for the functional regression estimator, is shown to give a signi cantly smaller mean square predicted error than that obtained with Bayesian methods. / Thesis / Master of Science (MSc)

Salmonella species continue to be commonly associated with cases of food-borne disease in developed countries. In the United States in 2001, the incidence per 100,000 people was highest for salmonellosis (15.1), followed by campylobacteriosis (13.8) and shigellosis (6.4). Enteric pathogens usually contaminate the surface of raw animal products during slaughter and primary processing (scalding, defeathering or dehiding, rinsing, cutting, mixing, and grinding, etc.) and can attach and/or reside in the regular and irregular surfaces of the skin, multiply and, thereafter, contaminate food preparation surfaces, hands and utensils. Trisodium phosphate (TSP) has been approved by the USDA as a sanitizer to reduce surface loads of Salmonella on chicken carcasses. A number of studies had demonstrated that TSP effectively removes surface contamination of carcasses by food-borne pathogens. However, very little scientific evidence is available which identifies the actual mechanisms of TSP antimicrobial activity and the response of food-borne pathogens exposed to TSP. This study examined both the physiological and molecular response of Salmonella enterica serovar Enteritidis to TSP treatment. The role of high pH during TSP treatment on its antimicrobial activity was examined. Adaptation of S. enterica serovar Enteritidis to TSP treatment was also examined by analyzing the proteome of serovar Enteritidis cells using two-dimensional gel electrophoresis and mass spectrometry. The role of high pH on the antimicrobial activity of TSP was examined using comparative studies involving treatment solutions containing different concentrations of TSP, treatment solutions adjusted to the equivalent pH as in each of the TSP treatments and TSP solutions pH adjusted to 7.0. Direct and indirect indices of cell survival, membrane damage, and cellular leakage were also employed to examine specific antimicrobial effects. Cell viability, loss of membrane integrity, cellular leakage, release of lipopolysaccharides and cell morphology were accordingly examined and quantified under the above treatment conditions. Exposure of serovar Enteritidis cells to TSP or equivalent alkaline pH made with NaOH resulted in the loss of cell viability and membrane integrity in a TSP concentration- or NaOH-alkaline pH-dependent manner. In contrast, cells treated with different concentrations of TSP whose pH was adjusted to 7.0 did not show any loss of cell viability or membrane integrity. These results indicate that TSP is a potent membrane-acting agent, and provide compelling evidence that high pH during TSP treatment was responsible for its antimicrobial activity. Adaptation of S. enterica serovar Enteritidis with a sublethal concentration of TSP resulted in the induction of the alkaline stress response. Alkaline stress response involves induced thermotolerance, resistance to higher concentrations of TSP, high pH and sensitivity to acid. Examination of the proteome of TSP-adapted cells revealed differential expression of a number of proteins but did not include the common heat shock proteins involved in thermotolerance. However, TSP adaptation caused a shift in the membrane fatty acid composition from unsaturated to a higher saturated and cyclic fatty acid. This shift in fatty acid composition increases the melting point of the cytoplasmic membrane so that it remains functional at high temperatures. Biofilm bacteria are more resistant to sanitizers, heat and antimicrobial agents than their planktonic counterparts. Examination of the proteome of TSP-adapted biofilm cell of S. enterica serovar Enteritidis revealed little overlap in the protein profile compared to TSP-adapted planktonic cells. Proteomic examination of planktonic and biofilm cells of S. enterica serovar Enteritidis revealed differential expression of a number of proteins involved in DNA replication, stress survival and transport of newly synthesized proteins. These results clearly indicate that changes in the expression of specific genes are involved in the biofilm mode of growth, which could play a significant role in resistance to antimicrobial agents. The results of the current study provide a better understanding of the mechanisms of antimicrobial action of TSP and also elucidate the response of S. enterica serovar Enteritidis to TSP and high pH adaptation. The study also raises new questions regarding stress tolerance of S. Enteritidis following TSP or alkaline pH adaptation with relevance to food safety.

Salmonella species continue to be commonly associated with cases of food-borne disease in developed countries. In the United States in 2001, the incidence per 100,000 people was highest for salmonellosis (15.1), followed by campylobacteriosis (13.8) and shigellosis (6.4). Enteric pathogens usually contaminate the surface of raw animal products during slaughter and primary processing (scalding, defeathering or dehiding, rinsing, cutting, mixing, and grinding, etc.) and can attach and/or reside in the regular and irregular surfaces of the skin, multiply and, thereafter, contaminate food preparation surfaces, hands and utensils. Trisodium phosphate (TSP) has been approved by the USDA as a sanitizer to reduce surface loads of Salmonella on chicken carcasses. A number of studies had demonstrated that TSP effectively removes surface contamination of carcasses by food-borne pathogens. However, very little scientific evidence is available which identifies the actual mechanisms of TSP antimicrobial activity and the response of food-borne pathogens exposed to TSP. This study examined both the physiological and molecular response of Salmonella enterica serovar Enteritidis to TSP treatment. The role of high pH during TSP treatment on its antimicrobial activity was examined. Adaptation of S. enterica serovar Enteritidis to TSP treatment was also examined by analyzing the proteome of serovar Enteritidis cells using two-dimensional gel electrophoresis and mass spectrometry. The role of high pH on the antimicrobial activity of TSP was examined using comparative studies involving treatment solutions containing different concentrations of TSP, treatment solutions adjusted to the equivalent pH as in each of the TSP treatments and TSP solutions pH adjusted to 7.0. Direct and indirect indices of cell survival, membrane damage, and cellular leakage were also employed to examine specific antimicrobial effects. Cell viability, loss of membrane integrity, cellular leakage, release of lipopolysaccharides and cell morphology were accordingly examined and quantified under the above treatment conditions. Exposure of serovar Enteritidis cells to TSP or equivalent alkaline pH made with NaOH resulted in the loss of cell viability and membrane integrity in a TSP concentration- or NaOH-alkaline pH-dependent manner. In contrast, cells treated with different concentrations of TSP whose pH was adjusted to 7.0 did not show any loss of cell viability or membrane integrity. These results indicate that TSP is a potent membrane-acting agent, and provide compelling evidence that high pH during TSP treatment was responsible for its antimicrobial activity. Adaptation of S. enterica serovar Enteritidis with a sublethal concentration of TSP resulted in the induction of the alkaline stress response. Alkaline stress response involves induced thermotolerance, resistance to higher concentrations of TSP, high pH and sensitivity to acid. Examination of the proteome of TSP-adapted cells revealed differential expression of a number of proteins but did not include the common heat shock proteins involved in thermotolerance. However, TSP adaptation caused a shift in the membrane fatty acid composition from unsaturated to a higher saturated and cyclic fatty acid. This shift in fatty acid composition increases the melting point of the cytoplasmic membrane so that it remains functional at high temperatures. Biofilm bacteria are more resistant to sanitizers, heat and antimicrobial agents than their planktonic counterparts. Examination of the proteome of TSP-adapted biofilm cell of S. enterica serovar Enteritidis revealed little overlap in the protein profile compared to TSP-adapted planktonic cells. Proteomic examination of planktonic and biofilm cells of S. enterica serovar Enteritidis revealed differential expression of a number of proteins involved in DNA replication, stress survival and transport of newly synthesized proteins. These results clearly indicate that changes in the expression of specific genes are involved in the biofilm mode of growth, which could play a significant role in resistance to antimicrobial agents. The results of the current study provide a better understanding of the mechanisms of antimicrobial action of TSP and also elucidate the response of S. enterica serovar Enteritidis to TSP and high pH adaptation. The study also raises new questions regarding stress tolerance of S. Enteritidis following TSP or alkaline pH adaptation with relevance to food safety.

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