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

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.

abstract: Cancer claims hundreds of thousands of lives every year in US alone. Finding ways for early detection of cancer onset is crucial for better management and treatment of cancer. Thus, biomarkers especially protein biomarkers, being the functional units which reflect dynamic physiological changes, need to be discovered. Though important, there are only a few approved protein cancer biomarkers till date. To accelerate this process, fast, comprehensive and affordable assays are required which can be applied to large population studies. For this, these assays should be able to comprehensively characterize and explore the molecular diversity of nominally "single" proteins across populations. This information is usually unavailable with commonly used immunoassays such as ELISA (enzyme linked immunosorbent assay) which either ignore protein microheterogeneity, or are confounded by it. To this end, mass spectrometric immuno assays (MSIA) for three different human plasma proteins have been developed. These proteins viz. IGF-1, hemopexin and tetranectin have been found in reported literature to show correlations with many diseases along with several carcinomas. Developed assays were used to extract entire proteins from plasma samples and subsequently analyzed on mass spectrometric platforms. Matrix assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) mass spectrometric techniques where used due to their availability and suitability for the analysis. This resulted in visibility of different structural forms of these proteins showing their structural micro-heterogeneity which is invisible to commonly used immunoassays. These assays are fast, comprehensive and can be applied in large sample studies to analyze proteins for biomarker discovery. / Dissertation/Thesis / M.S. Biochemistry 2012

Mass spectrometry is a versatile, powerful analytical tool for chemical and biomolecule identification, quantitation, and structural analysis. Tandem mass spectrometry is key component in expanding the capabilities of mass spectrometry beyond just a molecular weight detector. Another key component is the discovery of electrospray ionization allowing not only liquid samples to be ionized but also generation of multiply charged ions enabling mass spectrometry analysis of large biomolecules. The fragmentation pathway of ion during tandem mass spectrometry is highly dependent on the nature of the ion as well as the form of dissociation technique employed. To-date, no single form of ion or dissociation method can provide all the structure information needed; therefore, it is common to use multiple forms of ions, different charge carrier or modifications, with a variety of other dissociation techniques to generate complimentary information. Practically, it is not always easy to generate the desired form of ion via ionization methods and is one of the limitations. Gas-phase ion/ion reactions provide an easy approach in manipulation of ions, either through changing the ion type or covalent modifications, in the gas-phase with the goal of enhancing the capabilities of mass spectrometers for either molecular weight or structural analysis. In this dissertation, studies of new gas-phase ion/ion chemistry for biomolecules such as carbohydrates and phopho/sulfopeptides were performed, and exploration into mass spectrometry analysis of IgGs is discussed. <br><div> Ion/ion reactions with carbohydrates were investigated with the goal of finding a charge-transfer or covalent modification reaction which can increase the structural information of carbohydrates upon tandem mass spectrometry. No luck was achieved with charge transfer ion/ion reactions which increased the overall fragmentation information in tandem mass spectrometry. Novel gas-phase covalent chemistry was discovered where alkoxides were found to form ester and ethers. It was also discovered the aldehyde functional group at the reducing end of carbohydrates are susceptible to Schiff-base modifications. Schiff-base has been previously reported in peptides and this is the first time it has been discovered for carbohydrates.</div><div> In the next project a gas-phase approach for the rapid screening of polypeptide anions for phosphorylation or sulfonation based on binding strengths to guanidinium-containing reagent ions was developed. The approach relies on the generation of a complex via reaction of mixtures of deprotonated polypeptide anions with dicationic guanidinium-containing reagent ions and subsequent dipolar DC collisional activation of the complexes. The relative strengths of the electrostatic interactions of guanidinium with deprotonated acidic sites follows the order carboxylate</div><div> Hyaluronic acid, a linear carbohydrate polymer with repeating units of D-glucuronic acid and N-acetyl D-glucosamine, was found to exhibit unique properties in its electrospray ionization mass spectrum that was never seen before. Electrospray of hyaluronic acid in aqueous solution in the negative polarity presented an incredibly intriguing mass spectrum, which we termed “emerald city” consisting of max charge or max charge-1 anions of hyaluronic acid. This is the first biomolecule observed to have the capability to deprotonate at every acid site that is possible. These set of highly charge anions exhibits unique characteristics upon use as a charge inversion reagent to charged invert multiply protonated proteins. A max of thirty-three protons was transferred when myoglobin 24+ was charge-inverted to a max charge state of 9- in the negative mode. Further research should be conducted to fully understand this phenomenal and its possible utilities.<br></div><div> Lastly, mass spectrometry analysis of monoclonal antibodies was performed. Monoclonal antibodies are 150 kDa sized protein complexes and is a major area of interest for pharmaceutical industry. Mass spectrometry analysis of big proteins is an emerging area for mass spectrometry and is quite different compared to small and medium molecule analysis on the mass spectrometer. Detailed in the last chapter are methods developed for sample cleanup of immunoglobulin G as well as the application of q2 DDC for removal of loosely bound adducts to achieve sharper peaks in the mass spectrum. Studies of protein denaturation was also conducted with methods such as circular dichroism and differential ion mobility also employed. And finally, a photochemical reaction setup was shown to cleave twelve out of sixteen total disulfide bonds in the immunoglobulin G within seconds compared to traditional solution phase reactions which can take hours.<br></div>

<p> </p> <p>  Mass spectrometry (MS) plays an important role in nanomaterials research by facilitating the discovery of superatomic clusters and fullerenes, enabling the identification of atomically substituted clusters, and contributing to understanding mechanisms of cluster formation. In this dissertation, we used different mass spectrometry methods as well as ion soft-landing to address some of the ongoing challenges in cluster science. The first challenge is to extend the atom-by-atom substitution method, which is a promising strategy for designing new cluster-based materials, to a wider range of molecular clusters. Due to challenges associated with the synthesis, purification, and crystallization, this approach has been achieved only for a handful of gold and silver clusters. We extended this approach to enable the substitution of the first-row transitional metals into the core of Co6S8(PEt3)6 cluster, a well-defined metal chalcogenide superatomic cluster and a popular building block for designing novel 2D materials. This cluster is widely used in energy and electronic applications and is an excellent model system for computational studies of cluster-based materials. High-resolution MS analysis identified the formation of Co5MS8(PEt3)6+ (M=Mn, Fe, Ni) clusters, indicating that only Mn, Fe, and Ni atoms can be incorporated into the Co6S8 core using our synthetic method. A combination of mass spectrometric analysis and theoretical studies reaved that each heteroatom has different impact on the relative stability, core-ligand interaction, as well as optical, magnetic, and electrochemical properties of the cluster. </p> <p>Another challenge in the cluster science addressed in this work is the controlled activation of fully ligated clusters by ligand removal. Conventional activation methods such as thermolysis or chemical treatment do not provide sufficient control of the number of the removed ligands and often suffer from sintering of NCs as a result of excessive ligand removal and degradation of the destabilized NC cores. Using a specially-designed ion soft-landing instrument, we achieved a controlled removal of one or two phosphine ligands form the synthesized cobalt sulfide clusters using collision-induced dissociation (CID). The resulting fragments were mass selected and soft-landed onto surfaces. We found out that the reactivity of the fragment ions on surfaces may be controlled by altering the composition of the cluster core and ligand binding energy to the cluster. Although some of the fragments formed by removing one ligand including Co5FeS8(PEt3)5+ and Co6S8L(PPh3)5+ remain unreactive on surfaces, other fragments including Co6S8(PEt3)5+, Co5NiS8(PEt3)5+, and Co6S8(PEt3-xPhx) (x=1-2) undergo selective dimerization.  We observe that the reactivity of fragment ions produced by removing one surface ligand is controlled by the relative stability of the corresponding precursor ions towards fragmentation. In particular, fragment ions generated from more stable precursors undergo a selective dimerization reaction. In contrast, fragment ions produced from the least stable precursors remain largely unreactive on surfaces. In addition, we found that fragments generated by removing two surface ligands are highly reactive and undergo several nonselective reactions. This study demonstrates that fragment ions are unique building blocks that may undergo selective reactivity on surfaces to generate compounds that are difficult to prepare using conventional synthetic methods. We believe that the controlled preparation of fragment ions using ion soft-landing is a generalizable method to activate wide range of ligated nanoclusters which opens a direction for materials design and innovation.</p> <p>Finally, soft-landing of well-characterized redox-active polyatomic anions, PW12O403- (WPOM), was carried out to explore the distribution of pure mass selected anions on semiconducting vertically-aligned TiO2 nanotubes, which were used as a model system for 3D semiconductive materials. Energy dispersive X-ray (EDX) mapping analysis revealed that WPOMs form micron-size aggregates on top of the TiO2 NT and only penetrates 1-1.3 µm into the 10 µm-long nanotubes. This aggregation is attributed to the high resistance of TiO2. This is different from what we see on conductive substrates such as carbon nanotubes (CNTs) where a uniform distribution of ions is typically observed. This study provides valuable insight into the functionalization of porous semiconducting surfaces using mass selected ions for applications in energy storage and electronics.</p>

<p> An attempt was made to measure the yields of the stable cadmium isotopes produced in the thermal-neutron fission of 233U and 235U using a solid-source mass spectrometer. The results for 235U fission indicate that there is structure in the mass-yield curve for the region studied which takes the form of a depression around masses 112-114. The origin of this structure is discussed in terms of the various mechanisms which have been proposed to explain the nature of the mass distribution in the symmetric region.</p> <p> The 233U study was unsuccessful because of the experimental difficulties encountered, primarily the interference from terrestrial cadmium and the low recovery of the fission products. </p> / Thesis / Master of Science (MSc)

Orientadores: Isabel Cristina Sales Fontes Jardim, Sonia Cláudia do Nascimento de Queiros / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-18T09:46:45Z (GMT). No. of bitstreams: 1 Magalhaes_LouiseLeedaSilva_D.pdf: 920587 bytes, checksum: 2181b3ef5653dc834d474ffbb6be4574 (MD5) Previous issue date: 2011 / Resumo: Nos últimos anos, uma das considerações mais importantes no sistema produtivo de frutas é a capacidade de gerar produtos de qualidade e saudáveis, atendendo os requisitos de sustentabilidade ambiental, segurança alimentar e a viabilidade econômica, mediante a utilização de tecnologias não agressivas ao meio ambiente e à saúde humana. Métodos multirresíduos para determinação de agrotóxicos em frutas frescas são cada vez mais necessários, devido a sua importância em análises de rotina que envolve a saúde pública, o monitoramento ambiental e o comércio internacional. Os métodos de análise de resíduos de agrotóxicos em alimentos compreendem, basicamente, três etapas: a amostragem, o preparo de amostra e a separação e determinação dos analitos. O objetivo deste estudo consistiu no desenvolvimento de um método compreendendo o preparo de amostra, no qual foram empregadas as técnicas de extração líquido-líquido (ELL), extração em fase sólida (EFS) ou o método QuEChERS, a definição da separação, identificação e quantificação, rápida e eficiente, de alguns agrotóxicos aplicados em uva in natura, utilizando a cromatografia líquida de alta eficiência (CLAE) com detector por arranjo de diodos (DAD) ou por espectrometria de massas em série (EM/EM). O melhor método foi validado por meio do estudo dos parâmetros: precisão (repetibilidade e precisão intermediária), exatidão (recuperação), curva analítica, intervalo de linearidade, detectabilidade (limite de detecção, LD, e limite de quantificação, LQ), seletividade e robustez. O método de EFS seguido por CL-EM/EM mostrou-se linear em uma ampla faixa de concentração e os LQ obtidos, em nível de ng mL, permitiram que os limites máximos de resíduos (LMR) impostos pelas agências reguladoras fossem atingidos. Porém, o método que resultou em melhores recuperações, menor tempo de análise, identificações confiáveis e menor concentração detectável foi a extração pelo método QuEChERS seguida da determinação por CLEM/ EM / Abstract: In recent years, one of the most important considerations in fruit production is the ability to generate healthy products with high quality within the requirements of environmental sustainability, food security and economic viability, through the use of technologies that are not harmful to either the environment or health human. Methods for multiresidue determination of pesticides in fresh fruits are increasingly required due to their importance in routine analysis involving public health, environmental monitoring and international trade. The methods for analysis of pesticide residues in foods include three basic steps: sampling, sample preparation, and separation and determination of the analytes. The aim of this study was to develop a method of sample preparation using techniques such as liquid-liquid extraction (LLE), solid phase extraction (SPE), and the QuEChERS method, followed by separation, identification and quantification using high performance liquid chromatography (HPLC) with diode array detection (DAD) or tandem mass spectrometry (MS/MS), for a fast and efficient multiresidue method of some pesticides used in grape cultivation. The best methodology was validated through determination of the parameters: precision (repeatability and intermediate precision), accuracy (recovery), calibration curve, linearity range, detectability (detection limit (LOD) and limit of quantification (LOQ)), selectivity and robustness. The method using SPE and LC-MS/MS showed linearity over a wide concentration range and LQ at the level of ng mL, within the maximum residue limits (MRL) set by regulatory agencies. However, the method that resulted in improved recoveries, reduced analysis time, good detectability and reliable identifications was the QuEChERS method for extraction followed by LC-MS/MS / Doutorado / Quimica Analitica / Doutor em Ciências

The diploma thesis is focused on the determination of tetracyclines, sulfonamides and fluoroquinolones from soil. Antibiotics such as tetracycline, chlortetracycline, oxytetracycline. ciprofloxacin, trimethoprim, sulfamethaxazole and sulfadiazin were selected due to frequent use in veterinary medicine. Due to the fact that the soil is a complex matrix and contains many components that can interfere with the detection signal of analytes, it was necessary to use the MAX column in the SPE method, which removes fulvic aned humic acid from analytes and the HLB column Final analysis of the analytes was performed by liquid chromatography with mass detesction (LC-MS). The method was also used for real soil samples, which were delivered from ÚKZUS.

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