• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 58
  • 11
  • 6
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 91
  • 91
  • 91
  • 91
  • 24
  • 21
  • 20
  • 20
  • 20
  • 19
  • 17
  • 17
  • 12
  • 10
  • 9
  • 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.
71

Analysis of Synthetic Cannabinoids by Direct Analysis in Real Time Quadrupole Time-of-Flight Mass Spectrometry and Gas Chromatography Quadrupole Time-of-Flight Mass Spectrometry

Torbet, Tyler S 01 June 2015 (has links)
The aim of this study was to investigate the utility of direct analysis in real time quadrupole time-of-flight mass spectrometry and gas chromatography quadrupole time-of-flight mass spectrometry in the analysis of 162 different synthetic cannabinoids. Direct analysis in real time quadrupole time-of-flight mass spectrometry is shown to be a rapid and accurate analytical method for synthetic cannabinoids. Spectra can be generated with less than 1.5 ng of the drug in under a minute and be successfully searched against previously generated ESI-QTOF libraries in most cases (118/130 drugs tested) as well as can also be applied to the identification of synthetic cannabinoids in a mixture. Gas chromatography quadrupole time-of-flight mass spectrometry, while requiring a much longer analysis time, is shown to accurately distinguish all but 19 compounds (140/159). These two instruments have proven to be viable alternatives in synthetic cannabinoid analysis and will greatly benefit forensic laboratories.
72

MALDI-TOF MS for identification of Aspergillus species : A pilot study preceding possible implementation of MALDI-TOF MS to complement morphological assessment

Lindström, Christel January 2020 (has links)
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has revolutionized the field of bacterial diagnostics and is also used for routine analysis in smaller clinical laboratories. For identification of moulds, pre-analytical steps are more complicated and time consuming than for bacteria, and the choice of reference library has a big impact on the utility of MALDI-TOF MS. The aim of this study was to investigate if MALDI-TOF MS is applicable for identification of moulds belonging to the genus Aspergillus at the hospital laboratory in Gävle. Therefore, strains belonging to the genus Aspergillus and Penicillium, were analysed with MALDI-TOF MS after 2, 4 and 7 days of incubation. Two different extraction protocols were used and compared. Mass spectra were compared to reference spectra in two different databases: MSI-2 and RUO Compass library/BDAL (Bruker). Of the strains included, 97 % were correctly identified to species complex level with MSI-2. Only 25 % were identified to species level with RUO Compass library/BDAL (Bruker). However, totally 56 % were correctly identified to species complex level if a lower score value limit than recommended for identification, were applied. Significantly raised score values were observed with one of the protein extraction protocols used. Although, in most cases, the strains were considered identified to species complex level with either method. This pilot study conveys the feasibility of MALDI-TOF MS for identification of Aspergillus species in a clinical laboratory. While there are still issues to address, applying MALDI-TOF MS has the potential to allow for quicker and more precise identification, also in this specific clinical setting.
73

Interactions of slow multiply charged ions with large, free radiosensitizing metallic nanoparticles / Interaction d'ions multichargés lents avec des nanoparticules métalliques radiosensibilisantes

Mika, Arkadiusz 19 December 2017 (has links)
Cette thèse est consacrée à l'étude de l'interaction d'ions multichargés avec des particules métalliques de taille nanométrique. Ce travail a eu pour but d'étudier les processus fondamentaux ainsi que d'éclairer leur rôle comme radio-sensibilisants dans le traitement de cancer par hadronthérapie. Le nouveau dispositif développé dans ce cadre consiste en une source d'agrégats de type magnétron, d'une chambre de dépôt afin de permettre la caractérisation de la taille des nanoparticules neutres par analyse microscopique, et d'un spectromètre de masse par temps de vol capable de détecter des systèmes positivement chargés jusqu'à une masse de 50 000 ua. Les études de collisions ont été réalisées avec des agrégats de Bi (2 nm ; 200 atomes) et de Ag (6 nm ; 5000 atomes). Dans le deux cas, le processus de capture multiélectronique crée un système multichargé. Dans le cas du Bi, une grande partie fragmente par la fission asymétrique émettant des petits fragments. Dans le cas des particules plus grandes (Ag), les systèmes multichargés ne fragmentent pas, par contre des petits fragments sont aussi observés mais ils sont le produit de la pulvérisation de la nano-surface lors de collisions pénétrantes. En perspective, des expériences seront réalisées avec des nanoparticules métalliques fonctionnalisées ainsi que le comptage des électrons émis lors de la collision. / This thesis presents a study of the interaction of multiply charged ions with metallic nano-sized particles both in the context of fundamental processes and possible applications as radiosensitizers in nanoparticle-enhanced hadrontherapy. For this purpose a new experimental set-up has been constructed based on a magnetron-discharge cluster source, a deposition chamber for analyzing the size of neutral nanoparticles with AFM and TEM techniques and a time-of-flight mass spectrometer able to detect positively charged particles with masses up to 50 000 amu. Collision studies were performed with Bi clusters of 2nm in diameter, containing 200 atoms, as well as Ag nanoparticles (6 nm, 5000 atoms). In both cases multi-electron capture leads to the formation of multiply charged systems. In the Bi case a large fraction fragments by asymmetric fission emitting small singly charged fragments. In the case of large Ag nanoparticles multiply charged systems are stable. However, small size fragments are formed due to sputtering of the nano-surface in penetrating collisions. Future experiments will be performed with functionalized metal nanoparticles, aiming to count the number of electrons emitted after ion collisions.
74

Characterization of Secondary Organic Aerosol Precursors Using Two-Dimensional Gas Chromatography with Time of Flight Mass Spectrometry (GC×GC/TOFMS)

Roskamp, Melissa Jordan 05 September 2013 (has links)
The oxidation of volatile organic compounds (VOCs) plays a role in both regional and global air quality through the formation of secondary organic aerosols (SOA). More than 1000TgC/yr of non-methane VOCs are emitted from biogenic sources (significantly greater than from anthropogenic sources). Despite this magnitude and potential importance for air quality, the body of knowledge around the identities, quantities and oxidation processes of these compounds is still incomplete (e.g., Goldstein & Galbally, 2007; Robinson et al., 2009). Two-dimensional gas chromatography paired with time-of-flight mass spectrometry (GC×GC/TOFMS) is a powerful analytical technique which is explored here for its role in better characterizing biogenic VOCs (BVOCs) and thus SOA precursors. This work presents measurements of BVOCs collected during two field campaigns and analyzed using GC×GC/TOFMS. The first campaign, the Bio-hydro-atmosphere Interactions of Energy, Aerosols, Carbon, H2O, Organics & Nitrogen - Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS), took place in a Ponderosa pine forest in Colorado. The second campaign, Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT NOIR) Study, was conducted in the Ozark region of Missouri. Tens to hundreds of BVOCs were quantified in each set of samples, including primary emissions, atmospheric oxidation products, stress indicators and semi-volatile leaf surface compounds. These findings highlight that there is a largely uncharacterized diversity of BVOCs in ambient samples. Our findings demonstrate that GC×GC can distinguish between compounds with the same molecular weight and similar structures, which have highly variable potentials for production of SOA (Lee et al., 2006). This work represents some of the first analysis of ambient BVOCs with this technology, which is anticipated to contribute greatly to characterization of atmospheric SOA precursors and ultimately, regional and global modeling of SOA and fine particulate matter.
75

Chemical analysis of hazardous substances in permanent tattoo inks available on the market / Kemisk analys av skadliga substanser i permanenta tatueringsfärger tillgängliga på marknaden

Bevin, Anna, Lay, An Na, Ullmark, Daniel, Hagman, Jessika January 2020 (has links)
As permanent tattoos are becoming more popular and common, an increased number of allergic reactions to tattoos is reported. The purpose of this project was to analyze tattoo inks for hazardous substances, and whether they comply to current Swedish and European legislative requirements. The tattoo inks were qualitatively analyzed for pigments, and quantitatively analyzed for metals. A total of 73 tattoo inks were collected from various sources such as a tattoo ink supplier, online retailers, and provided directly from tattoo artists. The labels of each tattoo ink bottle were inspected to investigate their compliance with the Council of Europe and the Swedish Medical Products Agency. Matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-ToF-MS) was used to qualitatively analyze 20 selected tattoo inks for different pigments. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantitatively analyze trace metals in 70 of the samples. A large majority (90%) of the tested samples violated the requirements and criteria in the European resolution ResAP 2008(1), such as information on name and address of the manufacturer, minimum date of durability, sterility, batch number, and storage. Patch and allergy testing were incorrectly recommended for many samples in a way that is not accepted by dermatologists. In a worst-case scenario, this testing could be a sensitizing step. Also, it can not prevent future allergic reactions from occurring or provide any juridical insurance. Only one brand, World Famous, fulfilled the requirements for labeling for six of the seven samples (one sample failed due to a faulty declared pigment). The brands Tang Dragon and Dynamic did not fulfill any of the requirements listed in ResAP 2008(1). The list of ingredients was incorrect for all samples from Tang Dragon (bought prior to 2019 online). Also, six of the other 50 samples from different brands (World Famous, Intenze, Fusion Tattoo Ink, Eternal Ink, Solid Ink) declared at least one pigment incorrectly in their ingredients list. 25% of the declared and theoretically detectable pigments were detected by means of MALDI-ToF-MS, whereas the other pigments were either absent or below the limit of detection. Future analyses should include an MS/MS analysis. Polyethylene glycol (PEG) was identified qualatively in 15 of the 20 samples analyzed with MALDI-ToF-MS but was not listed in any of the ingredients lists. ICP-QQQ-MS is a very sensitive technique and could both detect and verify the presence of all metal-containing pigments, as well as the level of impurities. Copper was clearly more present in green and blue colors, regardless of the brand. The metal content was evidently dependent on the brand for arsenic, aluminum, bismuth, chromium, nickel, zinc, and strontium. Elevated levels of barium and strontium (partially very high levels: up to 727 mg/kg barium and up to 8.06 g/kg strontium) were found in several samples. High amounts of aluminum (4 to 11,0 g/kg) and titanium (as judged from white precipitates and ingredients lists) were present in most samples. Nickel (0.1 to 41 mg/kg) and chromium (0.1 to 139 mg/kg) were also present in the samples. Some other impurities were also present (arsenic – 3.8 mg/kg, mercury – 1.6 mg/kg, and lead – 5.4 mg/kg for one sample, respectively). Known sensitizing pigments were declared and partially confirmed by MALDI-ToF-MS in 17 of 53 samples of the brands Radiant Colour, Eternal Ink, Fusion Tattoo Ink, and Kuro Sumi. Four samples (from Intenze, Eternal Ink, and Kuro Sumi) also declared pigments listed as non-suitable substance according to the European Commission regulation on cosmetic products from 2009.
76

<b>How human activities and ventilation systems impact indoor air composition and chemistry in buildings</b>

Jinglin Jiang (5930687) 19 July 2024 (has links)
<p dir="ltr">As people in the U.S. spend 90% of their time indoors, their exposure to indoor air pollutants released during the use of household consumer products cannot be overlooked. Studies have shown that consumer products such as disinfectants, cleaning agents, and personal care products (PCPs) contain complex mixtures of volatile organic compounds (VOCs). Monoterpenes, added as active ingredients in cleaning agents and fragrances, are commonly detected in these products. Monoterpenes can react with ozone (O<sub>3</sub>) and initiate the formation of secondary organic aerosol (SOA). Siloxanes, another category of compounds commonly found in PCPs, can bioaccumulate and may adversely impact the environment and human health.</p><p><br></p><p dir="ltr">Most prior studies have evaluated chemical emissions from these products using offline techniques, such as sorbent tube sampling followed by gas chromatography-mass spectrometry (GC-MS). Few studies have been conducted during real-life use of these products in indoor environments. Considering that many indoor activities are often transient, the composition of indoor air can be rapidly altered. Real-time monitoring of indoor VOCs and aerosols is necessary to capture the temporal variations in emissions during indoor activities and to evaluate their impact on indoor air chemistry, human exposure, and outdoor air quality. In addition, O<sub>3 </sub>also plays an important role in indoor chemistry. Indoor O<sub>3 </sub>concentrations are strongly linked to ventilation system operation and occupancy patterns, as the ventilation from outdoors is the major source of indoor O<sub>3</sub> and occupants are a major sink of indoor O<sub>3</sub>. However, studies on how ventilation modes and occupancy impact spatiotemporal distributions of indoor O<sub>3 </sub>are limited.</p><p><br></p><p dir="ltr">Hazardous chemical incidents can potentially be another unexpected source of indoor pollutants, releasing volatile chemicals which can be transported to indoor environments via building ventilation. Evaluation of air, water, and soil contamination and human exposure risks is critical in the emergency response to hazardous chemical incidents, to develop effective remediation strategies. An effective and reliable approach to assess air, water, and soil contamination, and subsequent human exposures, is urgently needed.</p><p dir="ltr">To fill these research gaps, this dissertation aims to: (1.) characterize gas- and particle-phase emissions in real-time during common indoor activities, including surface disinfection, cleaning, and hair styling; (2.) evaluate the impact of indoor emissions on human health and the atmospheric environment; (3.) map the spatiotemporal distribution of O<sub>3</sub> and CO<sub>2</sub> concentrations throughout a building ventilation system; (4.) develop a methodology for rapid screening of VOCs in surface water samples collected from a chemical disaster site.</p><p><br></p><p dir="ltr">To achieve research goals (1.) and (2.), a field campaign was conducted at the Indiana University Research and Teaching Preserve (IURTP) field laboratory in summer 2019 and two field campaigns were conducted at the Purdue zero Energy Design Guidance for Engineers (zEDGE) Tiny House in fall 2020 and summer 2021 to characterize emissions from the use of cleaning agents, disinfectants, and hair care products in indoor environments, respectively. A proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) was used to monitor the mixing ratios of VOCs in real-time. To achieve research goal (3.), a multi-point sampling system was created at the Herrick Living Laboratories and its ventilation system in spring and summer 2019 to monitor spatiotemporal trends in O<sub>3 </sub>concentrations. To achieve goal (4.), a controlled static headspace sampling system, in conjunction with a high-resolution PTR-TOF-MS was developed to analyze surface water samples collected from East Palestine, Ohio, U.S. in the weeks after a train derailment and subsequent chemical spill and burn.</p>
77

Matrix-assisted laser desorption/ionization- quadrupole ion trap-time of flight mass spectrometry sequencing resolves structures of unidentified peptides obtained by in-gel tryptic digestion of haptoglobin derivatives from human plasma proteomes.

Sutton, Chris W., Glocker, M.O., Koy, C., Tanaka, K., Mikkat, S., Resch, M. 2009 July 1914 (has links)
No / Two-dimensional gel electrophoresis-separated and excised haptoglobin alpha2-chain protein spots were subjected to in-gel digestion with trypsin. Previously unassigned peptide ion signals observed in mass spectrometric fingerprinting experiments were sequenced using the matrix-assisted laser desorption/ionization-quadrupole ion trap-time of flight (MALDI-QIT-TOF) mass spectrometer and showed that the haptoglobin alpha-chain derivative under study was cleaved by trypsin unspecifically. Abundant cleavages occurred C-terminal to histidine residues at H23, H28, and H87. In addition, mild acidic hydrolysis leading to cleavage after aspartic acid residues at D13 was observed. The uninterpreted tandem mass spectrometry (MS/MS) spectrum of the peptide with ion signal at 2620.19 was submitted to database search and yielded the identification of the corresponding peptide sequence comprising amino acids (aa) aa65-87 from the haptoglobin alpha-chain protein. Also, the presence of a mixture of two tryptic peptides (mass to charge ratio m/z 1708.8; aa40-54, and aa99-113, respectively), that is caused by a tiny sequence variation between the two repeats in the haptoglobin alpha2-chain protein was resolved by MS/MS fragmentation using the MALDI-QIT-TOF mass spectrometer instrument. Advantageous features such as (i) easy parent ion creation, (ii) minimal sample consumption, and (iii) real collision induced dissociation conditions, were combined successfully to determine the amino acid sequences of the previously unassigned peptides. Hence, the novel mass spectrometric sequencing method applied here has proven effective for identification of distinct molecular protein structures.
78

Métodos rápidos para identificação microbiana aplicados ao monitoramento ambiental de salas limpas: ênfase na tecnologia MALDI-TOF / Rapid methods for microbial identification applied to clean room environmental monitoring: emphasis on MALDI-TOF technology

Andrade, Laíse de Oliveira 10 October 2017 (has links)
A espectrometria de massas baseada na tecnologia MALDI-TOF (do inglês, matrix-assisted laser desorption ionization-time of flight) (MALDI-TOF MS) tem sido cada vez mais incorporada à rotina de identificações microbiológicas nos laboratórios farmacêuticos de controle de qualidade, principalmente para as atividades do Programa de Monitoramento Ambiental de Salas Limpas. Isso porque o longo tempo necessário para a obtenção dos resultados por meio de métodos convencionais tem incentivado a procura por técnicas que permitam métodos rápidos. O objetivo deste trabalho foi avaliar a adequação da técnica MALDI-TOF MS para a identificação de bactérias isoladas do ambiente de salas limpas utilizadas em algumas etapas da produção de uma vacina viral. Treze espécies bacterianas conhecidas, normalmente isoladas das salas limpas estudadas, e cinco cepas ATCC foram identificadas pela técnica MALDI-TOF MS e por uma técnica bioquímica (BBL Crystal®). O desempenho da técnica MALDI-TOF MS foi superior ao da técnica bioquímica na identificação correta das espécies bacterianas (88,89% e 38,89%, respectivamente) e produziu menos identificações não confiáveis (5,55% e 22,22%, respectivamente). Os resultados evidenciaram que a técnica MALDI-TOF MS pode ser implementada para identificação rotineira de bactérias em um laboratório de controle de qualidade farmacêutico. Entretanto, a dependência de bases de dados exige estudos adicionais de isolados não identificados e, se apropriado, a adição destes a uma base de dados interna. O aperfeiçoamento de métodos de identificação microbiana é muito relevante no contexto de salas limpas, pois permitem ações corretivas e proativas essenciais para garantir a segurança microbiológica do processamento asséptico. / Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been increasingly introduced in routine microbiological identifications of pharmaceutical quality control laboratories, mainly for the activities of the Environmental Monitoring Program of Clean Rooms. The long time needed to obtain the results through conventional methods has stimulated the search for techniques that allow rapid methods, as MALDI-TOF MS. Thus, the objective of this work was to evaluate the suitability of the MALDI-TOF MS technique for the identification of bacteria isolated from the environment of clean rooms used in some stages of the production of a viral vaccine. Thirteen bacterial species commonly isolated from clean rooms studied and five strains ATCC were identified by MALDI-TOF MS technique and by a biochemical technique (BBL Crystal® System). Performance of MALDI-TOF MS was better than biochemical technique for correct species identifications (88.89% and 38.89%, respectively) and produced fewer unreliable identifications (5.55% and 22.22%, respectively). MALDI-TOF MS can be implemented for routine identification of bacteria in a pharmaceutical quality control laboratory. However, as a database-dependent system, maybe some isolated not identified by this technique must be additionally studied and, if appropriate, added to an in-house database.
79

Comprehensive two-dimensional gas chromatography (GCxGC ) for drug analysis

Song, Shin Miin, shinmiin@singnet.com.sg January 2006 (has links)
Separation technologies have occupied a central role in the current practices of analytical methods used for drug analysis today. As the emphasis in contemporary drug analysis shifts towards ultra-trace concentrations, the contribution from unwanted matrix interferences takes on greater significance. In order to single out a trace substance with confidence from a rapidly expanding list of drug compounds (and their metabolites) in real complex specimens, analytical technologies must evolve to keep up with such trends. Today, the task of unambiguous identification in forensic toxicology still relies heavily upon chromatographic methods based on mass spectrometric detection, in particular GC-MS in electron ionisation (EI) mode. Although the combined informing power of (EI) GC-MS has served faithfully in a myriad of drug application studies to date, we may ask if (EI) GC-MS will remain competitive in meeting the impending needs of ultra-trace drug analysis in the fut ure? To what extent of reliability can sample clean-up strategies be used in ultra-trace analysis without risking the loss of important analytes of interest? The increasing use of tandem mass spectrometry with one-dimensional (1D) chromatographic techniques (e.g. GC-MS/MS) at its simplest, considers that single-column chromatographic analysis with mass spectrometry alone is not sufficient in providing unambiguous confirmation of the identity of any given peak, particularly when there are peak-overlap. Where the mass spectra of the individual overlapping peaks are highly similar, confounding interpretation of their identities may arise. By introducing an additional resolution element in the chromatographic domain of a 1D chromatographic system, the informing power of the analytical system can also be effectively raised by the boost in resolving power from two chromatographic elements. Thus this thesis sets out to address the analytical challenges of modern drug analysis through the application of high resolut ion comprehensive two-dimensional gas chromatography (GC„eGC) to a series of representative drug studies of relevance to forensic sciences.
80

Vanadium Oxide Anions Clusters: Their Abundances, Structures and Reactions with SO₂

Wyrwas, Richard Ben, Jr. 22 November 2004 (has links)
Early transition metal oxide clusters have been a focus of study for several years. The production of vanadium oxide cluster anions in a pulsed helium flow reactor provides a relatively precise way of introducing defect sites and controlling the oxidation state of the vanadium atoms. The composition of the clusters can be changed from the V2O5 stoichiometry, where the vanadium atom is in a +5 oxidation state, to more reduced stoichiometries yielding a mixture of oxidation states containing atoms in the +2 oxidation state. The subsequent addition of reactant gases such as H2O and SO2 yields very intense adsorption reactions as well as a demonstration of the robustness of particular defect free clusters. For example, the cluster has been identified as a defect free cluster where all vanadium atoms are in the +5 oxidation state and all oxygen atoms are predicted to be in the 2- state. The cluster has been shown to not adsorb SO2- while clusters in a reduced oxidation state, such as and readily adsorb one or more SO2 molecules. The adsorption process has been shown to be size dependent, with the smallest monovanadium oxide anions being the most reactive.

Page generated in 0.0968 seconds