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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Electrifying the Molecules of Life : Peptide and Protein Analysis by Capillary Electrophoresis Coupled to Electrospray Ionization Mass Spectrometry

Wetterhall, Magnus January 2004 (has links)
<p>This thesis describes the current status and novel aspects of the analysis of the molecules of life, i.e. peptides and proteins, using capillary electrophoresis (CE) coupled to mass spectrometry (MS) via (sheathless) electrospray ionization (ESI). Early reports of sheathless CE-ESI-MS were plagued by limited lifetimes of the electrospray emitter. In this thesis, two new approaches, the Black Dust and the Black Jack methods, utilizing polymer-embedded graphite instead of noble metals are presented. These emitters have shown improved long-term stability and proven excellent for sheathless electrospray operation. Failure of an emitter is often caused by electrochemical reactions occurring at the emitter-liquid interface. The electrochemical properties of the graphite coated emitters were therefore evaluated by classical electrochemical methods, such as cyclic voltammetry and chronoamperometry. The graphite coated emitters showed excellent electrochemical stability and properties compared to noble metal and polymer configurations.</p><p>Analyte-wall interactions have long been known to cause problems in the CE analysis of biomolecules. This can be circumvented by internal modification of the capillary walls. Additionally, it is of outermost importance to have a stable and sufficiently high electroosmotic flow (EOF) to sustain the electrospray, when using a sheathless approach. New monomer and polymer coatings are presented for rapid and high-efficient CE-ESI-MS separations of peptides and proteins.</p><p>Furthermore, the use of CE-ESI coupled to Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) shows great potential for rapid proteomic probing of human cerebrospinal fluid. The results are comparable with more established techniques, such as liquid chromatography and two-dimensional gel electrophoresis coupled to MS. However, the CE-ESI-FTICRMS analysis has significantly lower sample consumption and faster analysis time compared to the other techniques. The applications and use of CE-ESI-MS is expected to have a bright future with continued growth as current trends of multidimensional hyphenation and microfabricated devices are further developed and explored.</p>
82

Liquid Chromatography – Mass Spectrometry Analysis of Short-lived Tracers in Biological Matrices : Exploration of Radiotracer Chemistry as an Analytical Tool

Lavén, Martin January 2005 (has links)
<p>Liquid chromatography – mass spectrometry (LC-MS) methods were developed for the analysis of positron emission tomography (PET) radiotracers in biological matrices. Additionally, radiotracer chemistry was explored as an analytical tool for supporting LC-MS method development and imaging molecular interactions in miniaturised chemical analysis systems.</p><p>Conventional radiodetection methods can offer high sensitivity in the analysis of radiotracers in biological matrices, although with the short half-life of PET tracers, this mass sensitivity decreases rapidly with time. This limits the time frame for analysis, and may compromise the precision and accuracy of the later measurements. Performing LC-MS analysis of the dominant stable isotope form of the tracer removes such time restrictions.</p><p>An LC-MS/MS method was developed for determination of the tracer flumazenil in human plasma, with high inter-assay precision (RSD < 7%) and accuracy (95 – 104%). The method was applied in a multiple scan PET study where the plasma concentration spanned from 0.07 to 0.21 nM. The method removed the time restrictions associated with radiodetection methods and thus provided the opportunity of analysing a greater number of samples than would have been possible with radioanalysis.</p><p>Furthermore, an LC-MS/MS method was developed that provided an efficient metabolic screening tool of potential PET tracers, whereby the substrates could be collected directly from 11C-labelling batches. This permitted repeated incubation experiments without the need of repeated labelling syntheses. A para-methoxy-benzamide analogue of the radiotracer WAY-100635 was thus identified as a potential tracer with improved metabolic stability. Additionally, a capillary LC-MS method was developed with rapid (0.75 min) and efficient (> 99%) on-line high flow-rate extraction for determination of metabolic stability of PET radiotracers.</p><p>Finally, the concept of radionuclide imaging of miniaturised chemical analysis systems was demonstrated with the direct study of interactions within capillary extraction columns and microchannels moulded in a plastic CD and poly(dimethylsiloxane).</p>
83

Development and Investigations of Novel Sample Preparation Techniques : Electrochemical Extraction and Evaluation of Miniaturized Analytical Devices Coupled to Mass Spectrometry

Liljegren, Gustav January 2005 (has links)
<p>Different sample preparation steps prior to a detection method are often essential in analytical chemistry. In this thesis, both static extractions and on-line coupled solid-phase extractions have been studied in combination with different detection techniques. Aspects of performing sample preparations in miniaturized analytical devices and the development of poly(dimethylsiloxane) (PDMS) microchips are discussed. Polypyrrole was also evaluated as an electrochemically controllable stationary phase for solid-phase microextraction (SPME) and solid-phase extraction (SPE).</p><p>The first part of this thesis describes the extraction of an organic compound from a very complex solid matrix utilizing the pressurized-fluid extraction (PFE) technique. The presented results show that PFE is easily optimized and enables rapid extractions and extracts relatively free from interferences.</p><p>An integrated three-electrode device, which enabled electrochemical (EC) SPME under potential control, was developed. With this device, both anions and cations could be extracted employing two types of polypyrrole films. Planar micro band electrodes positioned at the end of a capillary were also used to electrochemically extract and detect anions in a miniaturized flow system. Different analyte concentrations and preconcentration times were examined, and good linear correlations were found between the extraction time and the detection response. The on-line coupling of a thin layer EC cell, with a polypyrrole coated working electrode, to different mass spectrometric (MS) techniques is also described and evaluated. The results show that EC-SPE, employing polypyrrole as stationary phase, can be used as a preconcentration step prior to detection.</p><p>In addition, this thesis describes the development and on-line coupling of a microelectrode array equipped PDMS microchip with an integrated graphite electrospray emitter to electrospray ionization (ESI) MS. The system enabled short transfer times and an EC conversion efficiency of 30% at a flow rate of 0.5 μL/min. The on-line EC/ESI-MS experiments were significantly simplified using a wireless Bluetooth battery-powered EC instrument.</p>
84

Development of Enhanced Analytical Methodology for Lipid Analysis from Sampling to Detection : A Targeted Lipidomics Approach

Isaac, Giorgis January 2005 (has links)
<p>This thesis covers a wide range of analytical method development for lipid analysis in complex biological samples; from sample preparation using pressurized fluid extraction (PFE) and separation with reversed phase capillary liquid chromatography (RP-LC) to detection by electrospray ionization mass spectrometry (ESI/MS) and tandem MS.</p><p>The requirements for fast, reliable and selective extraction methods with minimal usage of solvents have accelerated the development of new extraction techniques. PFE is one of the new automated, fast and efficient liquid extraction techniques which use elevated temperature and pressure with standard liquid solvents. In this thesis the reliability and efficiency of the PFE technique was investigated for the extraction of total lipid content from cod, herring muscle and human brain tissue as well as for pesticides from fatty foodstuffs. Improved or comparable efficiencies were achieved with reduced time and solvent consumption as compared to traditional methods. </p><p>A RP-LC coupled online to ESI/MS for the analysis of phosphatidylcholine (PC) and sphingomyelin (SM) molecular species was developed and used for the analysis of brain lipids from eight groups of mice treated with vehicle and various neuroleptics. The effect of postnatal iron administration in lipid composition and behavior was investigated. Whether or not these effects could be altered by subchronic administration of the neuroleptics (clozapine and haloperidol) were examined. The results support the hypothesis that an association between psychiatric disorders, behavior abnormalities and lipid membrane constitution in the brain exists.</p><p>Finally, a tandem MS precursor ion scan was used to analyze the developmental profile of brain sulfatide accumulation in arylsulfatase A (ASA) deficient (ASA -/-) as compared to wild type control (ASA +/+) mice. The ASA -/- mice were developed as a model of the monogenic disease metachromatic leukodystrophy with an established deficiency of the lysosomal enzyme ASA. The results showed that an alteration in the composition of sulfatide molecular species was observed between the ASA -/- and ASA +/+ mice.</p><p>This thesis shows that modern analytical methods can provide new insights in the extraction and analysis of lipids from complex biological samples.</p>
85

Pressurized Fluid Extraction : A Sustainable Technique with Added Values

Waldebäck, Monica January 2005 (has links)
<p>The challenge for the future was defined by the Brundtland Commission (1987) and by the Rio Declaration (1992), in which the fundamental principles for achieving a sustainable development were provided. Sustainable chemistry can be defined as the contribution of chemistry to the implementation of the Rio Declaration. This thesis shows how Pressurized Fluid Extraction (PFE) can be utilized in chemical analysis, and how this correlates to Green Chemistry.</p><p>The reliability and efficiency of the PFE technique was investigated for a variety of analytes and matrices. Applications discussed include: the extraction of the antioxidant Irganox 1076 from linear low density polyethylene, mobile forms of phosphorus in lake sediment, chlorinated paraffins from source-separated household waste, general analytical method for pesticide residues in rape seed, total lipid content in cod muscle, and squalene in olive biomass. Improved or comparable extraction yields were achieved with reduced time and solvent consumption. The decrease in use of organic solvents was 50-90%, resulting in minimal volatile organic compounds emissions and less health-work problem. Due to higher extraction temperatures and more efficient extractions, the selection of solvent is not as important as at lower temperatures, which makes it possible to choose less costly, more environmentally and health beneficial solvents. In general, extraction times are reduced to minutes compared to several hours. As a result of the very short extraction times, the amount of co-extracted material is relatively low, resulting in fewer clean-up step and much shorter analysis time. Selective extractions could be obtained by varying the solvent or solvent mixture and/or using adsorbents. </p><p>In this thesis, the PFE technique was compared to the twelve principles of Green Chemistry, and it was shown that it follows several of the principles, thus giving a major contribution to sustainable chemistry. </p>
86

Electrifying the Molecules of Life : Peptide and Protein Analysis by Capillary Electrophoresis Coupled to Electrospray Ionization Mass Spectrometry

Wetterhall, Magnus January 2004 (has links)
This thesis describes the current status and novel aspects of the analysis of the molecules of life, i.e. peptides and proteins, using capillary electrophoresis (CE) coupled to mass spectrometry (MS) via (sheathless) electrospray ionization (ESI). Early reports of sheathless CE-ESI-MS were plagued by limited lifetimes of the electrospray emitter. In this thesis, two new approaches, the Black Dust and the Black Jack methods, utilizing polymer-embedded graphite instead of noble metals are presented. These emitters have shown improved long-term stability and proven excellent for sheathless electrospray operation. Failure of an emitter is often caused by electrochemical reactions occurring at the emitter-liquid interface. The electrochemical properties of the graphite coated emitters were therefore evaluated by classical electrochemical methods, such as cyclic voltammetry and chronoamperometry. The graphite coated emitters showed excellent electrochemical stability and properties compared to noble metal and polymer configurations. Analyte-wall interactions have long been known to cause problems in the CE analysis of biomolecules. This can be circumvented by internal modification of the capillary walls. Additionally, it is of outermost importance to have a stable and sufficiently high electroosmotic flow (EOF) to sustain the electrospray, when using a sheathless approach. New monomer and polymer coatings are presented for rapid and high-efficient CE-ESI-MS separations of peptides and proteins. Furthermore, the use of CE-ESI coupled to Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) shows great potential for rapid proteomic probing of human cerebrospinal fluid. The results are comparable with more established techniques, such as liquid chromatography and two-dimensional gel electrophoresis coupled to MS. However, the CE-ESI-FTICRMS analysis has significantly lower sample consumption and faster analysis time compared to the other techniques. The applications and use of CE-ESI-MS is expected to have a bright future with continued growth as current trends of multidimensional hyphenation and microfabricated devices are further developed and explored.
87

Development of Field-adapted Analytical Methods for the Determination of New Antimalarial Drugs in Biological Fluids

Lindegårdh, Niklas January 2003 (has links)
This thesis deals with the development of analytical methods for the determination of new antimalarial drugs in biological fluids. The goal was to develop methods that facilitate clinical studies performed in the field, such as capillary blood sampling onto sampling paper. Methods for the determination of atovaquone (ATQ) in plasma, whole blood and capillary blood applied onto sampling paper were developed and validated. Automated solid-phase extraction (SPE) and liquid chromatography (LC) with UV absorbance detection was used to quantify ATQ. Venous blood contained higher levels of ATQ than capillary blood after a single dose of Malarone (ATQ + proguanil). Ion-pairing LC was used to separate amodiaquine (AQ), chloroquine (CQ) and their metabolites on a CN-column. A method for quantification of AQ, CQ and their metabolites in capillary blood applied onto sampling paper was developed and validated. Perchloric acid and acetonitrile were used to facilitate the extraction of the analytes from the sampling paper. The liquid extract was further cleaned by SPE. Methods for the determination of piperaquine (PQ) in plasma and whole blood using SPE and LC were developed and validated. Addition of trichloroacetic acid (TCA) to the samples prior to injection into the LC-system significantly enhanced the efficiency for the PQ peak. Serum and whole blood contained higher levels (about 300 nM) of PQ than plasma (about 200 nM) after a single oral dose of 340 mg PQ. This indicates that PQ may be taken up in the leucocytes and thrombocytes.
88

Zwitterionic Separation Materials for Liquid Chromatography and Capillary Electrophoresis : Synthesis, Characterization and Application for Inorganic Ion and Biomolecule Separations

Jiang, Wen January 2003 (has links)
Liquid Chromatography (LC) and Capillary Electrophoresis (CE) are modern analytical techniques that play very important roles in many areas of modern science such as life science, biotechnology, biomedicine, environmental studies, and development of pharmaceutics. Even though these two techniques have existed and been subjected to studies for several decades, the developments of new separation materials for them are still very important till now in order to meet the different new demands for improvement from other disciplines in science. In this doctoral thesis, several novel covalently bonded sulfobetaine type zwitterionic separation materials are synthesized for the application in LC and CE. These materials carry both positively charged quaternary ammonium groups and negatively charged sulfonic groups, which result in a very low net surface charge compared to conventional separation materials with only anionic or cationic functional groups. Consequently, it is possible to employ these materials for separation of different ionic species under mild conditions. The surface properties have also been characterized, mainly by elemental analysis, sorption isotherm, ζ-potential measurements, and spectroscopic methods. By using packed zwitterionic columns for liquid chromatography, small inorganic anions or cations, and acidic or basic proteins can be independently and simultaneously separated in a single run using optimal sets of separation conditions. This is a unique property compared to conventional ionic separation material for LC. When fused silica capillaries coated with zwitterionic polymer are used for capillary electrophoresis, good separations can be achieved for solutes as different as inorganic anions, peptides, proteins, and tryptically digested proteins.
89

Reactions in the System Nitro-cellulose/ Diphenylamine with Special Reference to the Formation of a Stabilizing Product Bonded to Nitro-cellulose

Lindblom, Torbjörn January 2004 (has links)
The methods HPLC, microcalorimetry and FTIR together with chemometry, provide good analytical tools to follow the degradation of nitro-cellulose. The degradation products formed from diphenylamine (DPA) during storage can be followed with HPLC. FTIR, together with chemometry, also gives the precision needed for safety control of propellants. Nitro-cellulose (NC) containing DPA obtained a green colour already after 1 day storage at 70°C. About 10% of the stabilizer, and its derivatives, added were not extractable giving an extended time to autocatalysis. This time could be extended up to 70 days at 70°C for an extracted sample compared to about 3 days for non-stabilized NC. This was not shown before. Aged and extracted NC samples contained a non-extractable nitro compound. The most likely compound is 2,4´-dinitroDPA, probably bonded to NC via the amine nitrogen. The bonding to NC occurs after the formation of NNODPA. This is something not described before. Using another batch of nitro-cellulose to find out if a chemical bonding occurs gave inconclusive results as a blue NC was formed. Low molecular NC with high stability was obtained. A chemical bonding probably occurs when using NNODPA as a stabilizer, indicating NNODPA plays a key role. The use of FTIR/chemometry is a promising method to use when studying small chemical changes. The described methodology should be used to find out more about the compound(s) being bonded to NC.
90

Liquid Chromatography – Mass Spectrometry Analysis of Short-lived Tracers in Biological Matrices : Exploration of Radiotracer Chemistry as an Analytical Tool

Lavén, Martin January 2005 (has links)
Liquid chromatography – mass spectrometry (LC-MS) methods were developed for the analysis of positron emission tomography (PET) radiotracers in biological matrices. Additionally, radiotracer chemistry was explored as an analytical tool for supporting LC-MS method development and imaging molecular interactions in miniaturised chemical analysis systems. Conventional radiodetection methods can offer high sensitivity in the analysis of radiotracers in biological matrices, although with the short half-life of PET tracers, this mass sensitivity decreases rapidly with time. This limits the time frame for analysis, and may compromise the precision and accuracy of the later measurements. Performing LC-MS analysis of the dominant stable isotope form of the tracer removes such time restrictions. An LC-MS/MS method was developed for determination of the tracer flumazenil in human plasma, with high inter-assay precision (RSD &lt; 7%) and accuracy (95 – 104%). The method was applied in a multiple scan PET study where the plasma concentration spanned from 0.07 to 0.21 nM. The method removed the time restrictions associated with radiodetection methods and thus provided the opportunity of analysing a greater number of samples than would have been possible with radioanalysis. Furthermore, an LC-MS/MS method was developed that provided an efficient metabolic screening tool of potential PET tracers, whereby the substrates could be collected directly from 11C-labelling batches. This permitted repeated incubation experiments without the need of repeated labelling syntheses. A para-methoxy-benzamide analogue of the radiotracer WAY-100635 was thus identified as a potential tracer with improved metabolic stability. Additionally, a capillary LC-MS method was developed with rapid (0.75 min) and efficient (&gt; 99%) on-line high flow-rate extraction for determination of metabolic stability of PET radiotracers. Finally, the concept of radionuclide imaging of miniaturised chemical analysis systems was demonstrated with the direct study of interactions within capillary extraction columns and microchannels moulded in a plastic CD and poly(dimethylsiloxane).

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