National Repository of Grey Literature 142 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Determination of volatile and non-volatile nitrite products in sausages
Hlávka, Jan ; Sobotníková, Jana (advisor) ; Čabala, Radomír (referee)
This diploma thesis deals with the determination of nitrite products in sausages using gas chromatography. In the first part of this thesis, an extraction method was developed for the determination of 4-cyanophenol and N-nitrosoproline in samples of sausage products using gas chromatography with tandem mass spectroscopy. A 1% formic acid solution in acetonitrile was used to extract the analytes from the sausage samples. Due to the lower volatility of the analytes, derivatisation with N,O-bis(trimethylsilyl)trifluoroacetamide was necessary before each analysis. Using this method, an indicative determination of the concentrations of 4-cyanophenol and N-nitrosoproline in selected sausage samples was carried out. The standard addition method was used for the quantification of these analytes because of the strong matrix effect. For the selected types of sausage, it was observed whether or not the concentrations of the analytes differed in products with different meat contents. At the end of this diploma thesis, a validation of a method for the determination of volatile N-nitrosamines in sausage products by gas chromatography with chemiluminescence detection was performed. The analytes were N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosodibutylamine, N-nitroso-piperidine, N-nitrosopyrrolidine...
Capillary monolithic columns based on copolymer of styrene, divinylbenzene and methacrylic acid and their application for separations of small molecules.
Musilová, Adéla ; Coufal, Pavel (advisor) ; Čabala, Radomír (referee) ; Sýkora, David (referee)
This work is focused on the preparation and characterization of capillary monolithic columns based on a copolymer of styrene, divinylbenzene and methacrylic acid for the chromatographic separation of small molecules. The capillary monolithic columns were prepared in the quartz capillaries by one-step radical copolymerization reaction of monomers of styrene, divinylbenzene and methacrylic acid in the presence of toluene and isooctane as porogenic solvents and azobisisobutyronitrile as an initiator. The effect of incorporation of methacrylic acid into the polymerization mixture on the separation behavior and efficiency in reversed phase capillary liquid chromatography (CLC) and capillary liquid electrochromatography (CEC) was studied using a test mixture of compounds containing thiourea, phenol, aniline, benzene, toluene, ethylbenzene, propylbenzene and butylbenzene. The Walters test for reversed stationary phases was employed to evaluate the hydrophobicity of the prepared columns. Based on the calculated value of hydrophobicity index of 10.76, the prepared monolithic columns can be classified as very hydrophobic. Excellent repeatability of measurements in CLC mode and very good repeatability of the monolithic column preparation were achieved. The effect of polymerization time on the chromatographic...
Development and metrological evaluation of gas chromatographic methods for quality and safety control of alcoholic products
Korban, Anton ; Čabala, Radomír (advisor) ; Kubinec, Róbert (referee) ; Maier, Vítězslav (referee)
Dissertation is dealing with the development of methods of quality control of alcoholic products, particularly, with quantification of volatile congeners. Previously suggested "Ethanol as internal standard (IS)" method was compared with existing analytical methods of internal and external standardisation. After satisfactory results the method was validated in one laboratory and then an inter-laboratory study which included nine laboratories from four countries was conducted. It was shown that the method usage on GC-FID is beneficial due to the absence of necessity of internal standard compound addition into tested sample, and absence of tedious sample alcohol by volume (ABV) or density measurements. The algorithm of the method usage on GC-MS instruments was also suggested and developed. It was found out that MS detector sensitivity should be reduced in order to register ethanol signal successfully. For this aim it was suggested to employ less abundant 47 m/z ions during ethanol elution. These ions correspond to non-fragmented ethanol molecules containing one heavy isotope, mainly 13 C. According to the obtained results the suggested methodology allowed employing the "Ethanol as IS" method on GC-MS instruments with metrological properties better or similar as for the traditional IS method. The...
Enantioseparations of liquid crystalline materials
Vaňkátová, Petra ; Kubíčková, Anna (advisor) ; Čabala, Radomír (referee) ; Kohout, Michal (referee)
(EN) Liquid crystalline materials are an important domain of the material science. Chiral liquid crystals (CLCs) are researched for their unique chirality-derived properties. The development of new CLCs focuses both on appropriate molecular design to fit their intended purpose and also on ways of using widely available and less expensive sources of chirality to enable cost- effective production for a potential large-scale production. Methods capable of enantioseparation are needed mainly for chiral purity control of newly synthesized CLCs and for their potential use in scaling up for preparative purpose. Nowadays, enantioselective chromatography has evolved to be the method of choice for enantioseparations. This thesis aims to establish new approaches to chromatographic enantioseparations of CLCs by developing fast and robust enantioselective methods using two different ultra-high performance chromatographic techniques - sub/supercritical fluid chromatography (UHPSFC) and liquid chromatography (UHPLC). UHPSFC is introduced and successfully employed for the first time for this purpose. For some CLCs, high values of enantioselectivity and enantioresolution were achieved, opening the possibility of scaling up to semipreparative use. In UHPLC, two modes (reversed-phase and polar organic solvent mode)...
Quantification of main solution components by using fragments containing heavy nuclides of common elements
Horká, Blanka ; Čabala, Radomír (advisor) ; Bajer, Tomáš (referee)
Quantification of major components by gas chromatography with flame-ionization detector (GC-FID) is established in routine laboratory practice. The FID detector is considered as universal detector for gas chromatography (GC), but it does not provide a response for a wide range of compounds and GC-FID analysis provides only quantitative data. The coupling of gas chromatography with mass spectrometry is a powerful analytical tool that provides not only quantitative data but also qualitative data on the structure of substances. When quantified by GC-MS, the detector oversaturation is a problem as it is a highly sensitive detector (at ppb level). One way to avoid oversaturation of the detector is to significantly dilute the solutions, which causes a decrease in the sensitivity of the method. Another approach to bypass detector saturation is to interrupt detection during solvent elution. For quantification of the major components of solutions, only the first method of bypassing detector saturation can be applied, but it is a labor-intensive process that increases the measurement uncertainty. The interruption of detection during solvent elution is not applicable for the purpose of quantifying major components, so a new approach of quantifying major components of solutions using M+1 ions was proposed and...
Modern microextraction techniques for gas chromatographic analysis
Bursová, Miroslava ; Čabala, Radomír (advisor) ; Feltl, Ladislav (referee) ; Kubinec, Róbert (referee)
The submitted thesis is focused on the development, optimization, testing and practical application of the new microextraction method called Bell Shaped Extraction Device assisted Liquid-Liquid Microextraction (BSED-LLME). The method is based on the application of a miniature bell-shaped extraction tool in which the extraction takes place, so that only minimal solvent losses can occur, and which allows a reproducible dosing and collection of a small volume of the extraction solvent. The BSED- LLME method was used to preconcentrate selected volatile and less volatile analytes from aqueous samples into organic solvents of a density lower than water. After the extraction, the analytes were determined by fast gas chromatography with flame ionization detection and gas chromatography with mass spectrometry. The statistical methods known as Design of Experiment (DOE) were used for determination of the optimal extraction conditions for BSED-LLME procedure. DOE is based on a mathematical description of the system and the prediction of the optimal setting of experimental parameters that may influence extraction efficiency. Factors such as extraction time, volume of extraction solvent, addition of sodium chloride (ionic strength), stirring rate and the diameter of the extraction vessel ect., have been tested....
Structure and reactivity of anions of aromatic hydrocarbons
Obluková, Michaela ; Čabala, Radomír (advisor) ; Jašík, Juraj (referee)
This bachelor thesis deals with research about negative ions reactivity of aromatic hydrocarbons which occur in Titan's ionosphere - Saturn's moon. As an experimental method there was used tandem mass spectrometry with electrospray ionization technique, quadrupole mass analyzer and collision cell. The aim of this thesis was to contribute to the general understanding of processes in the Titan's ionosphere. Particularly there were performed experimental studies to created isomeric benzyne radical anions (o-, m-, p- C6H4˙- ) which were generated from phthalic, isophthalic and terephthalic acid and subsequently their reactions were explored with selected neutral gases in collision cell (C2H2, HC3N, CH3CN, SO2, O2).

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2 Čabala, Roman
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