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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.
181

Stationary phases for superheated water chromatography

Saha, Shikha January 2002 (has links)
This project focused on the comparison of conventional liquid chromatography and superheated water chromatography. It examined the differences in efficiency and retention of a range of different stationary phases. Alkyl aryl ketones and eight aromatic compounds were separated on PBD-zirconia, Xterra™ RP 18, Luna™ C18(2) and Oasis HLB™ columns using conventional LC and superheated water chromatography system. The retention indices were determined in the different eluents. On changing the organic component of the eluent from methanol to acetonitrile to superheated water considerable improvements were found in the peak shapes and column efficiencies on the PBD-zirconia and Oasis HLB™ columns.
182

Sobre a extratibilidade de cianeto-E ciano-complexos de trifenil-N-propil-fosfonio e trifenil-isopropil-fosfônio e algumas aplicações analíticas / About extractibility of cyanate-E cyano-complexes of the triphenyl-n-propyl-phosphonium and triphenyl-isopropyl-phosphonium and some analytical applications

Oliveira, Ruth Leme de 02 February 1971 (has links)
O estudo sistemático da extratibilidade de cianato e ciano-complexos de trifenil-n-propil e trifenil-isopropil-fosfônio, proporcionou a possibilidade de se efetuar, com eficiência, separações bem como de elaborar prova de identificação e métodos de determinação de interesse analítico. Mediante o emprêgo de íons cianato e de trifenil-isopropil-fosfônio, pôde-se estabelecer condições que permitiram extrair, do meio aquoso, íons de cobalto com 99,3% de eficiência (coeficiente de extração), em metil-isopropil-cetôna. Conseguiu-se, dessa maneira, separar baixos teores de cobalto de grandes quantidades de níquel. Pôde-se, assim, elaborar prova para a identificação de cobalto até 0,25 µg, com limite de diluição de l:2.000.000. A prova pode ser executada na presença de grande número de íons estranhos. O método quantitativo elaborado, além de possibilitar a separação dos ions Co(II) e Ni(II), permitiu determinar cobalto na faixa de concentração de 4 a 60 µg/ml, diretamente no extrato orgânico, por via espetrofotométrica, em 630 mµ. Isolou-se um composto correspondente à fórmula (Φ3-P-C3H7)2 [Co(OCN) 4] que se provou ser a espécie extraída no procedimento analítico. A marcante diferença de comportamento observada entre o ferrocianeto de trifenil-n-propil ou trifenil-isopropil-fosfônio e o correspondente ferricianeto, permitiu a elaboração de método para a separação quantitativa dêsses anions, mediante extração, em álcool pentílico, do ferricianeto -de trifenil-n-propilfosfônio, sendo o coeficiente de extração 97,5%. A medida espetrofotométrica, direta, do ferricianeto extraído, em 420 mµ, permite determinar 20 a 200 µg/ml. Entretanto, após reação, na própria fase orgânica, com íons Fe(II), a coloração azul obtida tornou o método cêrca de oito vêzes mais sensível e aplicável na faixa de 2 a 18 µg/ml, sendo a medida espetrofotométrica efetuada em 720 mµ. / O estudo sistemático da extratibilidade de cianato e ciano-complexos de trifenil-n-propil e trifenil-isopropil-fosfônio, proporcionou a possibilidade de se efetuar, com eficiência, separações bem como de elaborar prova de identificação e métodos de determinação de interesse analítico. Mediante o emprêgo de íons cianato e de trifenil-isopropil-fosfônio, pôde-se estabelecer condições que permitiram extrair, do meio aquoso, íons de cobalto com 99,3% de eficiência (coeficiente de extração), em metil-isopropil-cetôna. Conseguiu-se, dessa maneira, separar baixos teores de cobalto de grandes quantidades de níquel. Pôde-se, assim, elaborar prova para a identificação de cobalto até 0,25 µg, com limite de diluição de l:2.000.000. A prova pode ser executada na presença de grande número de íons estranhos. O método quantitativo elaborado, além de possibilitar a separação dos ions Co(II) e Ni(II), permitiu determinar cobalto na faixa de concentração de 4 a 60 µg/ml, diretamente no extrato orgânico, por via espetrofotométrica, em 630 mµ. Isolou-se um composto correspondente à fórmula (Φ3-P-C3H7)2 [Co(OCN) 4] que se provou ser a espécie extraída no procedimento analítico. A marcante diferença de comportamento observada entre o ferrocianeto de trifenil-n-propil ou trifenil-isopropil-fosfônio e o correspondente ferricianeto, permitiu a elaboração de método para a separação quantitativa dêsses anions, mediante extração, em álcool pentílico, do ferricianeto -de trifenil-n-propilfosfônio, sendo o coeficiente de extração 97,5%. A medida espetrofotométrica, direta, do ferricianeto extraído, em 420 mµ, permite determinar 20 a 200 µg/ml. Entretanto, após reação, na própria fase orgânica, com íons Fe(II), a coloração azul obtida tornou o método cêrca de oito vêzes mais sensível e aplicável na faixa de 2 a 18 µg/ml, sendo a medida espetrofotométrica efetuada em 720 mµ.
183

Evaluation of Human Toenail as a Non-invasive Biomonitoring Matrix for Assessing Human Exposure to Environmental Organic Pollutants by Optimized Sample Prep and GC/HRMS Analysis

Peterman, Paul Herbert 16 April 2019 (has links)
<p> Human biomonitoring is an analytical challenge to find environmental organic chemicals of varying polarity, persistency, and potential toxicity in a suitable, ideally non-invasive matrix at ppb levels that are significantly above method blanks. Compared with more traditional matrices of adipose tissue, serum, and urine, toenail clippings samples are non-invasive, compact, can be shipped without refrigeration, stored indefinitely at room temperature, and processed without concerns for biohazards. With both hydrophilic and hydrophobic layers, toenails contain 1-2% lipid, which is several times higher than serum. Toenails grow slowly and are trimmed every 2-3 months, which offers the potential to integrate both chronic and pulsed episodic exposures. Using toenail samples (65 to 340 mg) donated from four individuals and an indoor house cat, the hypothesis that toenails are a suitable biomonitoring matrix was tested by analyzing for persistent pesticides, over 50 PCB congeners, moderately persistent PBDEs, and transient compounds of triclosan and bisphenol A by using GC/High Resolution MS (GC/HRMS) analysis and for unsuspected compounds using GC/full scan MS. Although not fully digested and dissolved, toenails averaged 1.22% lipid (sd 0.20%, n=10). Lipid was separated and determined using a new small single-use 2-g S-X3 gel permeation chromatography flash column with high purity nitrogen. Multiple toenail samples from one individual were collected for over a year for replicate analysis, p,p&rsquo;- DDE averaged 0.82 ng/g-nail, sd 0.28, n=5 and 65.2 ng/g-lipid, sd 15.3, n=5 on lipid-adjusted basis. <i>Trans</i>-nonachlor averaged 3.08 ng/g-nail, sd 1.03, n=5; mean 254 ng/g-lipid, sd 97, n=5. PBDE 28 averaged 0.29 ng/g-nail, sd 0.10, n=5; mean 24.8 ng/g-lipid, sd 13.3, n=5. PBDE 85 averaged 0.25 ng/g-nail, sd 0.06, n=5; mean 20.8 ng/g-lipid, sd 6.2, n=5. PBDE 153 averaged 1.82 ng/g-nail, sd 0.51, n=6; mean 150 ng/g-lipid, sd 49.3, n=6. Most effectively biomonitored in toenails were normally transient triclosan (mean 58.3 ng/g-nail, sd 6.6, n=2), chlordanes, DDT, PBDEs, and PCBs including congeners with 2,5- or 2,3,6-chlorine substitution (PCBs 52, 49, 44, 70, 95, 101, 87, and 110), which are suspect neurotoxins, but are rarely found in extant serum biomonitoring data. Toenail soap wash samples indicated little (&lt; 4%) or no exogenous contamination, except for the musks galaxolide and tonalide in most samples, which ranged up to 30%, likely from topical application. The one cat toenail sample had elevated concentrations of PBDEs and especially chlordanes. Unsuspected tentatively identified compounds included a UV Filter compound, octocrylene, a hydroxyl-methyl benzothiazole, and several compounds used in flavors or fragrances.</p><p>
184

Development and Application of Novel Sample Introduction for Matrix Assisted Ionization and Solvent Assisted Ionization

Hoang, Khoa Duc Nguyen 25 April 2019 (has links)
<p> Mass spectrometry (MS) is an efficient analytical tool due to a number of advantages for providing high sensitivity, high-throughput analysis and less sample consumption. Since 1897, MS has continued to evolve and significant developments have occurred in the area of ionization techniques. Since 2010, inlet ionization techniques have shown the potential to compete in the areas of sensitivity and sample conservation with electrospray ionization (ESI) and matrix assisted laser desorption/ionization (MALDI). Matrix assisted inlet ionization (MAI) produces multiply charged ions within a mass spectrometer inlet without the need of high voltage, a laser or nebulizing gas. For MAI, sample preparation can be critical affecting the sensitivity, reproducibility and carry over. This dissertation presents new sample preparation techniques which have shown substantial improvement in sensitivity and reproducibility. The limit of detection can be achieved to less than 50 amol with the new sample preparation technique. Furthermore, this new sample introduction process enhance matrix assisted ionization (MAI) and solvent assisted ionization (SAI)&rsquo;s ability to couple with Thin-layer chromatography.</p><p>
185

The separation of the polar constituents of petroleum

Robson, William January 2018 (has links)
Identification of the heteroatom (nitrogen, sulphur, and oxygen; NSO)-containing compounds of petroleum is of key importance when considering industrial and environmental issues associated with crude oil production. The inherent molecular complexity of petroleum is such that detailed compositional investigations must ideally be preceded by some form of pre-fractionation. However, the more commonly performed methods of crude oil fractionation are often insufficient in the extent to which they separate oils, not allowing defined “molecular” fractions to be obtained and thus hindering more detailed investigations. The following work therefore focused on the development of chromatographic methods to aid in the characterisation of NSO compounds present within crude oils. A novel solid phase extraction (SPE) procedure was developed utilising both ion exchange and adsorption chromatography. The method enabled fractions broadly defined as ‘saturated’ hydrocarbons; ‘aromatic’ hydrocarbons; basic nitrogen compounds; naphthenic acids; phenols and other oxygen-containing species; carbazoles; sulfoxides; and thiophenes, to be isolated reproducibly and quantitatively from relatively small crude oil samples (~ 0.5 g). Assessment of method selectivity with a suite of ‘model’ compounds showed that the resulting fractions were quite well defined, with classes of ‘model’ compounds being isolated within discrete fractions. Application to five crude oils of widely varying properties and origins, such as API gravity (12.1−38.3°), demonstrated the potential for the wide-ranging use of the method. Sample recoveries were high (77−98%) with simple evaporative losses accounting for the majority of sample loss. Repeatability was also high, demonstrated by triplicate analyses of ‘model’ compound mixtures, oils spiked with ‘model’ compounds and oils alone. Subsequent, more detailed, analysis of the fractions using multidimensional gas chromatography-mass spectrometry (GC×GC-MS) and liquid chromatography-highresolution accurate mass-mass spectrometry (LC-HRAM-MS) showed the advantages of the new isolation method. For example, alkylated series (C1-5) of quinolines, carbazoles, fluorenones, dibenzothiophenes and xanthones were identified within their predicted fractions. Furthermore, comparison of mass spectra obtained from GC×GC-MS analyses with reference spectra resulted in the tentative identification of compounds hitherto not previously reported in crude oils, again illustrating the advantage of the isolation method. Novel series of thioxanthones, tocopherols (E vitamins) and terpenoidal sulfoxides and ketones were assigned within the isolated fractions. Following the successful evaluation of the method, the scheme was subsequently employed to investigate the effects of changing geochemical parameters on the composition of isolated NSO-containing compounds. For example, studies of NSO fractions from series of crude oils at different stages of thermal maturity or of biodegradation, led to the identification of a number of potential new molecular markers within the basic-nitrogen and ketone fractions. This work shows clear potential for the developed NSO isolation method to be used in further compositional studies as a tool to aid in geochemical investigations.
186

Development of NMR tools to investigate aggregation phenomena

Joyce, Rebecca Emily January 2013 (has links)
Chemistry and biology are full of examples of aggregation phenomena; from the useful applications in drug molecule stabilisation and tissue engineering, to the negative effects of causing diseases such as Alzheimer's and Parkinson's. NMR is a useful tool for probing aggregation as it can provide detail at the atomic scale; however, the molecular size of the aggregates can lead to poor resolution and spectral broadening, issues which require some development to solve. The research detailed in this thesis aims to develop NMR tools to investigate aggregation phenomena from two angles; firstly, to directly monitor aggregation using diffusion-ordered NMR spectroscopy and secondly to probe the effects of aggregates on biomimetic constructs using NMR techniques. To achieve the first aim, diffusion-ordered NMR Spectroscopy in conjunction with a size-exclusion chromatography stationary phase was developed for the purpose of monitoring aggregation in a time-resolved manner. The size-exclusion stationary phases, commonly used to separate molecules of different sizes, such as proteins from salts, in liquid chromatography methods, provide an additional perturbation of the diffusion profile of molecules of different sizes when added to NMR samples for diffusion-ordered spectroscopy analysis. The development of this method and a selection of applications are detailed within two chapters of the thesis. These studies have been published in Journal of Magnetic Resonancei and Journal of Physical Chemistry Cii. A complementary study of the interactions between aggregates and biological structures such as biomimetic cell membranes using NMR methods such as time-resolved 31P NMR and the implementation of paramagnetic shift reagents is discussed in the final two chapters. Changes in chemical shift caused by additional interactions between the shift reagent and the solvent are fully investigated and the method is applied to the study of membrane permeation by amyloid-β oligomers.
187

Super-resolution of photodynamic emitters by fluorescence fluctuation analysis

Boulineau, Rémi Louis Jean January 2014 (has links)
A range of fluorescence fluctuation analysis methods were developed and applied to labels commonly used in biological samples. Various super-resolution techniques were demonstrated in vitro and in vivo using objective-type Total Internal Reflection Fluorescence Microscopy (TIRFM). An experimental Fluorescence Correlation Spectroscopy (FCS) setup was developed along with associated post-acquisition data algorithms. The technique was applied to investigate the stoichiometry of a protein subunit of ribonucleotide reductase (RNR). FCS method was adapted with an Electron Multiplying Charge Coupled Device (EMMCD) detection scheme and applied to inorganic Quantum Dots (QDs) diffusing in solutions of different viscosities. Super-resolution Optical Fluctuation Imaging (SOFI) algorithm was implemented in ImageJ software and conclusive results obtained on reference samples of QDs and combed DNA. Potential applications of temporal correlation analysis to the study of diffusive processes and single particle tracking were also discussed. A new super-resolution technique applicable to multiple adjacent fluorescent molecules called Direct Object Resolution by Image Subtraction (DORIS) was developed and tested with QD complexes. The method enables one to accurately map the position of two emitters displaying intermittency in their fluorescence emission and separated by a distance below the diffraction limit, without the need of complex instrumentation or analysis. The technique relies on the subtraction of the Point Spread Function (PSF) of each single fluorescent probe, and is in theory applicable to any blinking or flickering dye. The principle was first demonstrated on simulated data and experimentally on QDs coupled by 100-basepair double-stranded DNA constructs. Super-resolution by image subtraction was further applied in vivo in S. pombe cells, where distances between clustered fluorescent fusion proteins were accurately determined. The selective activation of photoswitchable probes mEos3 was exploited to optimise the DORIS subtraction process and provided a simple method to determine the relative positions of closely spaced emitters within an aggregate, as encountered in association sites or multimeric complexes.
188

Multiplexed Single-cell Spatial Proteomics and Transcriptomics

January 2018 (has links)
abstract: Single-cell proteomics and transcriptomics analysis are crucial to gain insights of healthy physiology and disease pathogenesis. The comprehensive profiling of biomolecules in individual cells of a heterogeneous system can provide deep insights into many important biological questions, such as the distinct cellular compositions or regulation of inter- and intracellular signaling pathways of healthy and diseased tissues. With multidimensional molecular imaging of many different biomarkers in patient biopsies, diseases can be accurately diagnosed to guide the selection of the ideal treatment. As an urgent need to advance single-cell analysis, imaging-based technologies have been developed to detect and quantify multiple DNA, RNA and protein molecules in single cell in situ. Novel fluorescent probes have been designed and synthesized, which targets specifically either their nucleic acid counterpart or protein epitopes. These highly multiplexed imaging-based platforms have the potential to detect and quantify 100 different protein molecules and 1000 different nucleic acids in a single cell. Using novel fluorescent probes, a large number of biomolecules have been detected and quantified in formalin-fixed paraffin-embedded (FFPE) brain tissue at single-cell resolution. By studying protein expression levels, neuronal heterogeneity has been revealed in distinct subregions of human hippocampus. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2018
189

Evaluation of a Technique to Quantify Lipids in Bivalve Larvae Crassostrea virginica Gmelin, using Nile Red and Epiflourescence Microscopy

Perez, Laura Liliana Castell 01 January 1991 (has links)
No description available.
190

Utilization of a Helium Discharge Detector for Quantitation of Organohalogen Compounds

Ryan, David andrew 01 January 1989 (has links)
No description available.

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