• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 135
  • 6
  • 2
  • Tagged with
  • 143
  • 117
  • 110
  • 90
  • 47
  • 47
  • 45
  • 35
  • 22
  • 20
  • 20
  • 18
  • 18
  • 18
  • 17
  • 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.
61

Vývoj, optimalizace a validace analytické metody na stanovení těkavých mastných kyselin ve vodných vzorcích metodou GC/MS

OPEKAR, Jan January 2018 (has links)
This thesis is focused on the development of an analytical method for the determination of volatile fatty acids in aqueous samples using GC-MS/MS. The theoretical section provides general information on a selected group of acids, their significance in the biogas plants, the means of their derivatization and the analytical techniques used. The practical part mainly deals with optimizition of various parameters in the derivatization reaction to achieve optimal conditions. Finally, the analytical method was successfully validated and applied to the analysis of a real sample.
62

Analýza směsi produktů katalytické oxidace metodou plynové chromatografie s použitím směšovače s řízeným odpařováním / Analysis of catalytic oxidation product mixture using gas chromatography method and controlled evaporation mixer

Haupt, Josef Michael January 2016 (has links)
The goal of this master's thesis was to develop a method for gas chromatography using the Controlled Evaporation Mixer (CEM) for gas mixture sampling. Gas mixture contained chemical substances formed during manufacturing of acrylic acid by two-step oxidation of propylene. The analyzed mixture composed of permanent gases, light hydrocarbons and compounds containing oxygen. During the method development several capillary columns with polar and nonpolar stationary phase were used. After selection of the most suitable column (SPB-1 Sulfur, Supelco, USA) the method was further optimized for the maximal possible separation efficiency. However, it was impossible to separate propane and propene on SPB-1 Sulfur column. These gases were possible to determine on TCD detector and separate on respective columns prior to the detector. For that purpose, the optimization of multiple-port valves switching inside the gas chromatograph was performed. The next step was calibration of gas chromatograph for a purpose of quantitative analysis of selected substances. The calibration solution containing solvent and an analyte was evaporated and diluted with nitrogen by CEM to obtain desired analyte concentration. Formaldehyde and propane had a very low response on detectors, acetaldehyde was undetectable in desired...
63

Analýza fosfolipidů metodou komprehenzivní plynové chromatografie / Analysis of phospholipids by comprehensive gas chromatography

Šilhavecká, Simona January 2017 (has links)
Phospholipids are an important group of polar lipids constituting the main component of cell membranes. Their proportion may vary depending on many factors of the surrounding environment in which the cell is located. Determination of membrane phospholipids is essential in many scientific, industrial and economic sectors. The aim of this work has been to develop a separation method for determination of membrane phospholipids by which it was possible to analyze phosphorylated parts of phospholipids and fatty acids from one sample. Comprehensive gas chromatography with mass detection (GC×GC-MS) was chosen for the assay. This method allows the separation of the entire sample on two serially connected different columns, among which is the interface called modulator. The preparation of the sample includes a cleavage of the phospholipid molecule by the enzyme phospholipase C, which released the phosphorylated polar headgroups. These polar parts had to be derivatized before analysis. The principle of the chosen derivatization consisted in the use of two different silylation agents (hexamethyldisilazane and N,O-Bis(trimethylsilyl) trifluoracetamide) in two steps. Conditions were selected for efficient separation of the silylderivatives of phosphorylated headgroups using GC×GC-MS using a cryogenic...
64

Hormony v čistírenských kalech / Hormones in sewage sludge

Jagošová, Klára January 2018 (has links)
Currently there is a spate of interest in the presence of pharmacologically active substances in the environment. These substances are excreted in active or metabolized form and with wastewater pass the wastewater treatment plant. Current treatment technologies do not always eliminate all pharmaceuticals effectively and therefore they enter the environment. One of these active groups is the group of steroid hormones. Steroid hormones belong to the group of endocrine disruptors and they are considered to be dangerous for the ecosystems. Due to the hydrophobic character of steroid hormones they undergo partial or total sorption from wastewater to sludge. Sewage sludge is the by product of wastewater treatment and contains heavy metals, organic contaminants and pathogenic bacteria. A part of produced sewage sludge is used as a fertilizer in the Czech Republic. This issue follows the regulation 347/2016 – conditions of agricultural use of sewage sludge. Waste policy of EU will alter the conditions of sludge disposal, so it is necessary to obtain data about the concentration levels, fate and behaviour of those pollutants. This thesis was focused on five natural female hormones and four synthetic, which are used as a part of contraceptive pills and substitutional hormonal therapy. Determination of hormones was performed in four steps including ultrasonic assisted extraction, clean up by solid phase extraction, derivatization and final analysis by gas chromatography with mass spectrometry on triple quadrupole in MS/MS mode.
65

Analýza organických látek přítomných v biouhlu / Analysis of organic substances present in biochar

Bača, Ondřej January 2021 (has links)
This master's thesis deals with the analysis of organic substances, which are present in biochar. Biochar contains a number of organic compounds, that can be toxic and also carcinogenic to living organisms. In order for biochar to be used to improve soil quality or to be used for other applications, its safety must be declared by European or international certifications. Relevant European and international standards have been created for the determination of organic substances, that could be present in biochar. The theoretical part of the thesis was focused on selected organic substances, the process of pyrolysis and thermochemolysis, biochar characterisation and the used analytical methods. The experimental part of the thesis consisted of extraction with toluene and after that the determination of concentration of the 38 polycyclic aromatic hydrocarbons was performed. Qualitative analysis was performed by two-dimensional gas chromatography. Biochar samples were also subjected to thermochemolysis method and then they were analysed on GC-MS again. In both analytical methods, a large number of substances from groups such as PAHs, carboxylic acids, amines, substituted naphthalenes etc. was found, as well as smaller number of eg. polychlorinated biphenyls.
66

Problematika perfluorovaných sloučenin ve složkách životního prostředí / Issues of perfluorinated compounds in the environmental compartments

Kalášek, Stanislav January 2008 (has links)
Perfluoroalkylated substencies are priority organics polutants. They are evolved to the environment from many sources. We classify them as new xenobiotics which are present in the environment. There will be described their chemical, physical and environmental properties in theoretical part and there will be described the analytical chemistry of these substancies in varios types of environmental samples. There will be developed metod for their identification and quantification. For this assignment will be use especially chromathografic methods. There will be developed standard operation procedure. The procedure will be verify on real environmental samples.
67

Studium průniku vybraných degradačních produktů syntetických polymerů do životního prostředí / Study of the selected synthetic polymer degradation products penetration into enviromental compartments

Tobiášová, Tereza January 2008 (has links)
The subject of this thesis is the study of the degradation of polyurethanes in the weather conditions on the waste dumps and observation of the penetration of the potential degradation products into the environment.
68

Analýza degradačních produktů organického barviva po rozkladu v diafragmovém výboji / Analysis of organic dye degradation product after decomposition in diaphragm discharge

Nejezchleb, Martin January 2009 (has links)
The diploma thesis is focused on the identification of degradation products of organic dye Saturn Red L4B resulting by degradation in diaphragm discharge, using separation techniques with mass spectrometric detection.
69

Využití plynové chromatografie pro stanovení reziduí léčiv ve vodách / Aplication of gas chromatography for determination of drug residuals in waters

Lacina, Petr January 2009 (has links)
Diploma thesis is focused on the choose of methods and optimalisation analysis procedure of selected pharmaceuticals (salicylic acid, ibuprofene, naproxene, ketoprofene and diclofenac) in surface and waste water by using gas chromatography with mass spectrometer (GC-MS). Solid-phase extraction (SPE) with Oasis HLB cartridges was used as an extraction method in this analysis. Extraction is followed by derivatization and their optimalization of selected pharmaceuticals. Derivatization and its optimalization were performed by two silylation reagens N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA). Different volumes of derivatization reagents, different temperatures and different times were used during the procedure. The best combination is then used for analysis of real samples. Real samples of waste water were collected in sewage treatment plants in Brno – Modřice and real samples of surface water were collected from several rivers and one pond in region Moravia. This thesis also presents and tests SPE methods for extraction and concentration selected sulfonamide residues (sulfamethazine, sulfamethoxazole, sulfapyridine and sulfathiazole) from the aquatic environment.
70

Analýza vonných látek v kosmetických prostředcích metodou plynové chromatografie / Analysis of aroma compounds in cosmetics by gas chromatography

Divišová, Radka January 2009 (has links)
This thesis is focused on aroma compounds which are presented in a wide variety of products including perfume, cologne, cosmetics, toiletries, laundry products and detergens. The widespread use and exposure to aroma compounds of aforementioned products could cause a range of the adverse reactions such as contact dermatitis, asthma, eczema and breathing problems. There are a lot of aroma compounds triggering negative allergic reactions but EU regulations limit 26 the most important fragrance allergens. The presence of these substances has to be declared on the product label if a limit of 0,01 % for rinse off and 0,001 % for leave-on products is exceeded. Of these 26 substances, a methodology was elaborated for determination of 12 allergens in a experimental part of this thesis. A method by solid-phase microextraction (SPME) and gas chromatography-flame ionization detection (GC-FID) was applied for fragrance allergens identification, extraction and measurement. The optimal extraction conditions of SPME-GC method were investigated including equilibrium time, extraction time and extraction temperature to increase extraction efficiency. Another important point is the method by SPME-GC-FID was validated and following performance parameters were determined: repeatability, linearity, limit of detection (LOD) limit of quantitation (LOQ). SPME-GC-FID was tested and applied to real samples.

Page generated in 0.0651 seconds