published_or_final_version / abstract / toc / Medical Sciences / Master / Master of Medical Sciences

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Investigations of new applications of the inductively coupled plasma (ICP) for analytical atomic emission spectroscopy are performed. Research efforts are focused in three major areas: emissions below 185 nm, analysis of wear metals in lubricating oils and use of the ICP as a selective detector for high performance liquid chromatography (HPLC). A unique plasma coolant tube containing a side arm which allows direct observation of the discharge is used to investigate emissions in the vacuum ultraviolet (VUV) spectral region between 120 and 185 nm. Emissions from elements which do not emit radiation in the visible region are observed. Oxygen emissions at 130 nm, nitrogen at 149 and 174 nm and carbon at 155 and 165 nm make up the background spectrum. These elements are present as impurities in the argon gas used to sustain the ICP discharge. Fifteen emission lines from bromine are observed. Those at 153 and 163 nm are the most intense. Sulfur also has fifteen emission lines and chlorine has nine in this region of the spectrum. The VUV region is found useful for observation and potential analysis of many elements. A heated sample introduction system attached to a Babington nebulizer is investigated as a means to aerosolize lubricating oils for introduction into the ICP. This allows direct analysis of wear metals in oil samples without requiring the usual sample dilutions. Several commercial brands and weights of motor oil are spiked with iron in order to evaluate this system. Heating the oil as it enters the nebulizer is found to increase the nebulization efficiency as much as sixtyfold in some cases. Differences in nebulization efficiency due to viscosity are almost entirely eliminated through the application of heat. A linear calibration curve extending three orders of magnitude from a detection limit of one ppm iron is determined. The ICP is used as a selective detector for HPLC. Nucleotides separated by anion exchange chromatography are determined in the ICP by observing phosphorus emissions. Methanol and acetonitrile used for reverse phase HPLC are successfully run in the IPC. The method is evaluated by using the ICP to determine phosphorus in compounds separated by using reverse phase conditions. The HPLC is used to separate organic interferences from several silicone samples using reverse phase conditions allowing the ICP to accurately analyze silicon content.

Investigation and control of alkylsilane stationary phase structure in reversed phase liquid chromatography is presented. Raman spectroscopy is used to probe the alkyl chain conformational order and interchain coupling as a function of various chromatographic conditions. A new method is further developed to fabricate alkylsilane stationary phases with controlled surface coverage. The alkyl chain conformational order and interchain coupling of a series of high-density docosylsilane (C22) bonded stationary phases is shown as a function of temperature, surface coverage, polymerization method, common solvents and solutes. The conformational order of C22 stationary phases is compared to that of octadecylsilane (C18) stationary phases to understand the chain length effect on stationary phase structure. The conformational order information as indicated by Raman spectral order indicators for a C22 phase are correlated with the capacity factor and separation efficiency for each solute studied to gain insight into the retention mechanism. These studies help to understand the origin of stationary phase shape selectivity and the separation process in general. Based on these results, the molecular pictures at the stationary phase/solvent interface are proposed. The effect of pressurized solvent environments on two C18 phases is studied to obtain direct evidence for changes in stationary phase structure due to pressure. These changes are compared to effects of solvation relative to air in the same solvents. In addition, Raman spectral order indicators are identified for perdeuterated alkyl-containing system. This study provides a foundation for studying stationary phase structure in complex systems comprised of long alkyl-containing solutes.A further development of a new method is presented as well for synthesizing alkylsilane stationary phases with precisely controlled surface coverage by using a displaceable surface template monolayer of n-alcohol. A mechanism for this process is proposed based on the studies of n-alcohol concentration and chain length effect on the stationary phase surface coverage. The utility of these new stationary phases as chromatographic support is demonstrated. The shape selectivity for these new phases is comparable to or better than similar phases prepared by conventional methods.

Burkholderia pseudomallei is the causative agent of Melioidosis, an endemic disease in South East Asia, and is classified as a category B biological agent. Currently, there is no licensed vaccine for this disease; the mortality rate is high due to the incorrect diagnosis and the pathogen insusceptibility to general antibiotics. A mass spectrometry based proteomic approach has been applied in order to identify the proteins that are responsible for pathogenicity.Methods were developed for the proteomic analysis of Burkholderia species using B. vietnamiensis G4, an opportunistic pathogen as the model organism. Both gel-based (LC-MS/MS) and gel-free MudPIT (LC/LC-MS/MS) approaches have been applied for the analysis of the proteins extracted from four different cellular fractions of these bacteria. More than 1200 proteins were identified from these analyses, including many proteins previously identified as virulence factors of these bacteria. Similar methodologies were applied to build a proteome map of non-pathogenic B. thailandensis E264 to use as a reference for the pathogenic studies. Additionally, proteomes of two B. thailandensis strains isolated from two geographical locations were compared to investigate the differences in protein expression of these organisms.Proteins identified from pathogenic B. pseudomallei were compared with the non-pathogenic B. thailandensis and opportunistic pathogen B. vietnamiensis proteins. Many species specific proteins were identified from this proteomic analyses; those proteins can be used as antigen targets to selectively identify these pathogenic bacteria in a complex biological matrix using affinity capture methods.Ticks are vectors that can transmit disease causing pathogens one host to another. Knowing the pathogen reservoir is important in order to control disease spread in the environment. Application of mass spectrometric methods to identify the host blood components from tick vectors was investigated using tick nymphs which feed only once in their life cycle. Using mass spectrometry based proteomics; host specific proteins like hemoglobin and immunoglobulin were identified from a single tick nymph analysis. Additional studies have examined the fatty acid profiles of rabbit and sheep blood fed tick nymphs using SPALDI mass spectrometry. Different fatty acid profiles were obtained for these tick nymphs, but further investigations are required to validate these findings.

No description available.

Metaproteomics, as a proteomic approach to analyse environmental samples, is a new and expanding field of research. The field promises new ways of determining the status of the organisms present in a sample, and could provide additional information compared to metagenomics. Being a novel field of research, robust methods and protocols have not yet been established. In this thesis, we examine several methods for a reliable extraction of protein from soil and periphyton samples. The extraction should preferably be fast, compatible with downstream analysis by mass spectrometry and extract proteins in proportion to their presence in the original sample. A variety of methods and buffers were used to extract proteins from soil and periphyton samples. Concentration determinations showed that all of these methods extracted enough protein for further analysis. For purification and digestion of the samples, several methods were used. The purified samples were analysed on three different mass spectrometers, with the Orbitrap Velos Pro delivering the best results. The results were matched against four genomic and metagenomic databases for identification of proteins, of which the UniProt/SwissProt database gave the best result. A maximum of 52 proteins were identified from periphyton samples when searching against UniProt/SwissProt with strict settings, of which the majority were highly conserved proteins. The main limitation for this type of work is currently the lack of proper metagenomic databases.

Selenium has been shown to have multiple biochemical effects ranging from nutrient deficiency at low levels to toxicity at high levels. This duality of concern has led to a demand for increased numbers of highly accurate and precise determinations of selenium in biological materials. A convenient procedure was developed for determining selenoamino acids by HPLC-THG-AAS, based on the derivatization of these analytes with Sanger's reagent. Selenomethionine, selenocystine and selenocysteine (after blocking the free selenol group with phenylmercurio cation) were converted to their N-2,4-dinitrophenyl derivatives, and separated on a Nucleosil 5-NO$ sb2$ column with methanolic mobile phase containing acetic acid and triethylamine. Furthermore, an improved HPLC-AAS interface design was modified and optimized for the detection of selenium in HPLC column eluate. The new design was (i) compatible with aqueous mobile phases containing volatile buffers and (ii) provided equivalent molar response to analytes containing Se($-$II), Se(+IV) and Se(+VI). A method for simultaneously determination of selenate, selenite, selenocystine, selenomethionine and selenoethionine was developed by using the HPLC-AAS system with aqueous acetic acid containing ammonium acetate as eluate solution on the cyanopropyl column. The equivalent low ng limits of detection (1-2 ng as Se) for different oxidation states of selenium analytes were obtained using several different mobile phases and/or columns. A phenol extraction procedure for selenate, selenite, selenocystine, selenomethionine and selenoethionine was evaluated for the determination of these selenium analytes in natural waters and wheat samples. The current HPLC-AAS system provides an inexpensive alternative to conventional techniques for the determination of selenium analytes in environmental samples.

Standards of Amadori rearrangement products (ARP) were synthesized for the purpose of developing analytical techniques and performing mechanistic studies related to their thermal decomposition. Several synthetic strategies were explored. An HPLC analytical system with a diode array detector was coupled to a fluorometer and an electrochemical detector, in order to detect simultaneously and on-line, a wide variety of degradation products of ARPs and to follow their kinetics. The potential of such a system to analyze complex Maillard mixtures was demonstrated. The kinetics of the reaction of glucose with morpholine (a Strecker inactive analogue of proline was used in order to simplify the kinetics) to produce Amadori morpholine was studied under experimental conditions that minimize side reactions and maximize Amadori product formation. At specific time intervals, the samples were analyzed for the presence of reactants and Amadori product by the multidetector HPLC system. Color and fluorescence were also measured. The data obtained were used to calculate the rate constants for the formation and degradation of Amadori product. A mechanistic model that statistically fitted the kinetic data was proposed. To further understand the details of the decomposition mechanism of Amadori proline, different mass spectrometric experiment were performed. High resolution, linked-field scan and neutral loss experiments have indicated that 1-((2$ sp prime$-carboxyl)pyrrolidinyl)-1-deoxy- scD-fructose (Proline Amadori product) followed two main pathways of fragmentation under electron impact conditions; one initiated by the ring oxygen and the other by the amino acid nitrogen, producing two well stabilized fragment ions; oxonium and imminium ions. In addition, ortho-elimination reactions initiated by O or N-centered radical sites were shown to produce the most intense peaks and diagnostically important ions for the identification of Amadori products. However this approach can only pro

The need for selective and inexpensive detectors in liquid chromatography is of considerable interest in the determination of sulfur compounds. Of the available-selective sulfur methodologies, flame photometric detector coupled to gas chromatography is the most widely used. It has proven to be a sensitive and selective method for detection of heat stable and volatile sulfur compounds. Fundamentally, this technique is not applicable to high boiling and/or thermolabile sulfur compounds. More recently, hyphenated flame photometric detector has been utilized, with limited success, to monitor sulfur species in liquid chromatography. However, existing HPLC-FPD methodologies have never been applied to real samples, due to the low population of S 2, the emitting species, and the quenching effects of the other species present in the flame. / In this work, two total consumption high-performance liquid chromatography flame photometric (HPLC-FPD) interfaces compatible with either methanolic or aqueous mobile phases are described and optimized for monitoring low volatile and thermally fragile sulfur compounds in biological samples. Each interface was fuelled either by methanol or by hydrogen. The all quartz interfaces enclosed four consecutive thermal processes: (a) thermovaporization of the HPLC effluent; (b) pyrolysis of the organic matrix (including sulfur species) in a kinetic H2/O2 flame; (c) conversion of the oxidized sulfur compounds to H2S in a reducing post-combustion stage fuelled by hydrogen; and (d) transport of the generated hydrides towards a hydrogen radical rich surrounding of an inverted hydrogen-oxygen diffusion flame. Chemiluminescence induced in the last step was integrated as a narrow beam in a light-guide positioned remotely from the analytical cool flame and oriented towards a photomultiplier unit. Radioisotopic assays demonstrated that sulfur (as H235SO4) was transferred quantitatively to the analytical flame. Indirect evidence suggested that sulfur was hydrogenated in the post-combustion step via a thermochemical hydride generation process to mediate the formation of S2. The linearity of calibration graphs (0.9950 < r < 0.9986), where r is the correlation coefficient) and unprecedented HPLC-FPD limits of detection for sulfur compounds (1.5 etag/s for 2-methylthiophene, 2.25 etag/s for carbon disulfide, and 4.5 etag/s for ethanesulfonic acid) allowed for the speciation of sulfur species in garlic extracts. Alternatively, modification of the methanol fuelled interface to a hydrogen fuelled reactor allowed detection of thiosulfinates and high molecular weight sulfur compounds in horse kidney and garlic extracts, respectively.