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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.
11

Evaluation of Non-Contact Sampling and Detection of Explosives using Receiver Operating Characteristic Curves

Young, Mimy 07 November 2013 (has links)
The growing need for fast sampling of explosives in high throughput areas has increased the demand for improved technology for the trace detection of illicit compounds. Detection of the volatiles associated with the presence of the illicit compounds offer a different approach for sensitive trace detection of these compounds without increasing the false positive alarm rate. This study evaluated the performance of non-contact sampling and detection systems using statistical analysis through the construction of Receiver Operating Characteristic (ROC) curves in real-world scenarios for the detection of volatiles in the headspace of smokeless powder, used as the model system for generalizing explosives detection. A novel sorbent coated disk coined planar solid phase microextraction (PSPME) was previously used for rapid, non-contact sampling of the headspace containers. The limits of detection for the PSPME coupled to IMS detection was determined to be 0.5-24 ng for vapor sampling of volatile chemical compounds associated with illicit compounds and demonstrated an extraction efficiency of three times greater than other commercially available substrates, retaining >50% of the analyte after 30 minutes sampling of an analyte spike in comparison to a non-detect for the unmodified filters. Both static and dynamic PSPME sampling was used coupled with two ion mobility spectrometer (IMS) detection systems in which 10-500 mg quantities of smokeless powders were detected within 5-10 minutes of static sampling and 1 minute of dynamic sampling time in 1-45 L closed systems, resulting in faster sampling and analysis times in comparison to conventional solid phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) analysis. Similar real-world scenarios were sampled in low and high clutter environments with zero false positive rates. Excellent PSPME-IMS detection of the volatile analytes were visualized from the ROC curves, resulting with areas under the curves (AUC) of 0.85-1.0 and 0.81-1.0 for portable and bench-top IMS systems, respectively. Construction of ROC curves were also developed for SPME-GC-MS resulting with AUC of 0.95-1.0, comparable with PSPME-IMS detection. The PSPME-IMS technique provides less false positive results for non-contact vapor sampling, cutting the cost and providing an effective sampling and detection needed in high-throughput scenarios, resulting in similar performance in comparison to well-established techniques with the added advantage of fast detection in the field.
12

Development of new solvent-free microextraction techniques for the analysis of volatile organic compounds: application to the use of breath analysis as a toxicological tool for explosure analysis

Alonso Roura, Mònica 14 December 2012 (has links)
Hippocrates predicted many years ago that breath could tell something related with our health. On his treaties, he indicated that when the body starts moving after sleeping, and breathe with more frequency, something hot and acid is expelled with air. It is possible to predict a disease from breath, but it has not been until recent years that last developments in breath analysis has allowed to detect compounds precisely and to associate the presence of these compounds to certain diseases. The use of breath analysis in clinical diagnosis and exposure to contaminants presents great advantages as this is a non-invasive technique, compared with other techniques such as blood or urine analyses. Two new instrumental methodologies have been developed in the present thesis, which are based on adsorbent micro-traps, specifically designed for the analysis of volatile compounds in breath and environmental samples. These equipments are versatile and low cost, compared to other commercially available instrumentations. One of the methodologies developed has been designed for the analysis volatile compounds in breath samples, showing efficiency and resolutions unknown up to know. It has allowed detecting exposure to volatile contaminants in a range of concentrations that the current techniques cannot achieve. The second equipment has been developed for the analysis of the same contaminants in other biological matrixes, in this case blood. It has been used to assess the mechanism followed by the inhaled compounds when entering the human body. These new methodologies were evaluated in different exposure studies. 2,5-dimethylfurean was detected with a high sensitivity and allowed to determine the smoking habits of a wide group of individuals, also 48 hours after smoking. The levels of contamination due environmental tobacco smoke were also evaluated in different environments. The high sensitivity of the developed techniques allowed us to demonstrate the contamination of passive smokers by environmental tobacco smoke (ETS) after few hours of being in contact with. Breath levels of the smoking biomarker after few hours in contact with ETS where at the same level that those found in smokers who smoke few cigarettes per day / Que l’alè ens deia alguna cosa de la nostra salut ja ho va intuir Hipòcrates. Al Tractat Mèdic hi va escriure: “Així, doncs, quan el cos es posa en moviment després de dormir i respira amb més freqüència, quelcom calent i àcid és expulsat amb l’aire. D’això en venen malalties si hom no pren precaucions.” Sí, de l’olor de l’alè s’intuïen malalties però no ha estat fins als darrers anys, que els nous avanços en les tècniques d’anàlisi no han proporcionat els mecanismes adients per detectar els compostos de forma inequívoca i poder associar la seva presència a l’alè a determinades malalties. Tant des d’un punt de vista mèdic com d’exposició a contaminants, el principal avantatge de poder disposar d’una anàlisi d’alè consisteix en la metodologia diagnòstica, que no és invasiva i, per tant, no presenta els inconvenients associats a altres tècniques convencionals, com son l’anàlisi de sang i d’orina. En aquesta tesi s’han desenvolupat dos noves metodologies instrumentals, basades en micro-trampes d’adsorció, especialment dissenyades per a l’anàlisi de compostos volàtils en mostres gasoses, principalment mostres ambientals i mostres d’alè humà. Aquests nous equipaments es caracteritzen per la seva versatilitat i molt baix cost, si es comparen amb els equips comercials actuals. Un dels prototips s’ha dissenyat per a l’anàlisi de mostres d’alè, mostrant una eficàcia i resolució desconeguda fins ara, el que ha permès detectar l’exposició a contaminants volàtils a uns nivells que les tecnologies actuals no permeten assolir. El segon equipament ha estat desenvolupat per permetre analitzar els mateixos contaminants en matrius biològiques, en aquest cas sang, i poder determinar de quina manera i en quin percentatge els compostos que inhalem per exposició arriben a entrar en el cos humà. Aquestes noves metodologies s’han avaluat en diferents estudis d’exposició. S’ha pogut detectar un compost, el 2,5-dimetilfuran, amb una elevada sensibilitat per a la detecció de l’hàbit fumador de les persones, inclús després de més de 48 h d’haver fumat una cigarreta. També s’han estudiat els nivells de contaminació pel fum ambiental del tabac que tenen lloc en diferents ambients (locals de fumadors i no-fumadors). L’elevada sensibilitat de les tècniques desenvolupades ha permès demostrar “in-situ” per primera vegada que els fumadors passius només requereixen unes poques hores de contacte en un ambient contaminat pel fum del tabac per presentar nivells de contaminació a l’alè similars als dels fumadors de poques cigarretes al dia
13

Chirální analýza syntetických vonných látek ve vodním ekosystému / Chiral analysis of musk compounds in water ecosystem

Švarcová, Lucie January 2014 (has links)
Diploma thesis summarizes available information about chiral analysis of synthetic musk compounds in the aquatic environment. In the theoretical part of the thesis chirality and importance of chiral analysis by means of examples of different environmental pollutants is documented. Further consideration is aimed on musk compounds, their classification, characteristics and their fate in the environment, especially in the aquatic environment. After that methods for chiral analysis of synthetic musk compounds are reviewed. The aim of the experimental part of this diploma thesis was to carry out the determination of thirteen representatives of musk compounds (2-cyclohexylethanol, allylcyklohexylpropionate, Arocet, Aroflorone, Citronellol, Fresco Menthe, Galaxolide, hexyl cinnamic aldehyde, HSA, isoamylsalicylate, isobornylacetate, Lilial and Linalool), out of which some compounds are chiral and some are achiral. For the analysis samples of wastewater from the wastewater treatment plant Brno - Modřice were taken. Target compounds were isolated by solid phase microextraction (SPME) and were subsequently analyzed by gas chromatography with flame ionization and mass spectrometric detection. On the basis of data evaluation the removal efficiency forgiven musk compounds in the wastewater treatment plant was assessed.

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