National Repository of Grey Literature 13 records found  1 - 10next  jump to record: Search took 0.01 seconds. 
Analysis and Biochemistry of Less Current Steroids - Neuroactive Steroids and Their Sulfates
Včeláková, Helena ; Hill, Martin (advisor) ; Ventura, Karel (referee) ; Meloun, Milan (referee)
Disertation work brings new findings in the field ofbiochemistry and analysis of neuroactive steroids. The pubrications invorved to the dissertation work dear with biochemicar anarysis of neuroactive steroids and its apprication in biomedicine. Some endogenous steroids can act as efficient neuromodurators' These substances are known as neuroactive steroids' If they are synthesized directly in the central nervous system, they have been named the neurosteroids (Schreiber 1980; corpechot, Rober et ar. rggl). some of the neuroactive steroids act as neuroactivators, the others are neuroinhibitors (Kimonides, Khatibi et al. l99g; Kaasik, Kalda et al. 2001; Lockhart, Warner et al. 2002). The neuroactive steroids operate usually as modulators of membrane receptors (GABA_ receptors and NMDA_receptors) responsible for the permeability of ion channels in neuronal cells. Generally, while physiologic functions and pharmacokinetics of endogenous neuroactive steroids studied on animals was investigated (Wang, Wahlstrom et al. 1997; Norberg, Backstrom et al. 19gg), the number of studies concerning neuroactive steroids in human body fluids and tissues in connection with physiology is insufficient (Bicikova, Tallova et al. 2000; Strohle, Romeo et al. 2003). The main problem is probably laboriousness of corresponding...
Polymethacrylate monolithic columns in capillary liquid chromatography
Grafnetter, Jan ; Coufal, Pavel (advisor) ; Pacáková, Věra (referee) ; Ventura, Karel (referee) ; Sýkora, David (referee)
3 Conclusions This Thesis gives chromatographic and structural characteristics of the butyl methacrylate monolithic columns prepared for the capillary liquid chromatography. Results of this Thesis clearly demonstrate the possibility of preparation of capillary monolithic columns with a good repeatability of the principal chromatographic parameters. A completely new technique for preparation of the monolithic columns for use in the on-column detection mode was introduced. Different photometric detection modes were applied to monolithic capillary columns in CLC. The advantages and disadvantages of the on-column detection mode in comparison to the additional detection capillary were studied and described. It was shown that the best separation and the most sensitive quantification in the short analysis time could be reached by using the monolithic columns with detection window placed directry on the separation capillary, just after the stationary phase or within the monolith. The attempts leading to preparation of chiral monolithic stationary phases, which would allow enantioseparation of selected chiral analýes' were not totally successful. No time was left to find the suitable chromatographic conditions for enantioseparations. \ I
Toxicity of Organic Mixtures
Reitmajer, Josef ; Feltl, Ladislav (advisor) ; Čabala, Radomír (referee) ; Ventura, Karel (referee) ; Mejstřík, Viktor (referee)
6. CONCLUSION The aim of this study was to test additiviý of chemical compounds in distribution process between two phases and to compare distribution coefficients K-;^ for different molar ratio of mixture with acute toxicity index EC50 gained on oligochaeta Tubifex tubifex. Mixtures of organic solvents ethanol, benzene, aniline and nitrobenzene were studied. Deviations from additivity were found for distribution coefficients of all tested mixtures. The most significant deviation exhibited benzene - ethanol mixture. The lowest deviations were observed for mixture ethanol - aniline. The results obtained indicate that the partition coefficient K.;* behave similarly as acute toxiciý. Definitely it is for benzene - ethanol mixture. It is possible to suppose that this parameter might be used for estimation of changes in acute toxicity of mixtures. The aim of the second part of the thesis was to study how distribution of chemicals changes with concentration and composition of mixture. Variations in distribution of mixture components beťween gaseous and aqueous phase were found. The highest deviations were found for benzene - ethanol and benzene - eniline mixtures. No deviation was found for mixture aniline - nitrobenzene. Deviations were not as significant as in first part of study. Dependences of distribution...
Nano-fibers as a modern extraction sorbents for extraction of samples in chromatographic analysis
Raabová, Hedvika ; Šatínský, Dalibor (advisor) ; Ševčík, Juraj (referee) ; Ventura, Karel (referee)
Charles University, Faculty of Pharmacy in Hradec Králové Training workplace Department of Analytical Chemistry Doctoral degree program Pharmaceutical Analysis Candidate Mgr. Hedvika Raabová Supervisor prof. RNDr. Dalibor Šatínský, Ph.D. Advisor assoc. prof. PharmDr. Lucie Chocholoušová Havlíková, Ph. D. Title of Doctoral Thesis Nanofibers as modern extraction sorbents for sample extraction in chromatographic analysis Extraction techniques represent one of the most common approaches to sample handling. The analytes of interest can be isolated easily even from complex matrices, especially by solid-phase extraction (SPE). Therefore, this technique became very popular and routinely used in laboratories. The variety of commercially available sorbents has made this method even more attractive. Nevertheless, the new sorbent materials are still looked for because of the broadening spectrum of analyzed substances and the increasing demands on selectivity and extraction efficiency. Nanomaterials have been increasingly associated with these properties over the last ten years. Therefore, they are receiving more and more attention related to extraction procedures. The dissertation thesis is focused on the application of nanofibrous polymers as innovative sorbents for solid-phase extraction. First, the...
Development and optimization of a robust pressure modulator for multidimensional gas chromatography
Ston, Martin ; Čabala, Radomír (advisor) ; Ventura, Karel (referee) ; Jelínek, Ivan (referee)
Comprehensive gas chromatography (GC×GC) is a modern and advanced analytical method designed to separate very complex samples, when the separation efficiency of classical gas chromatography is not sufficient. GC×GC allows complete simultaneous analysis of a sample on two different columns, interconnected by special interface called the modulator. Three types of control units were set up and a robust pulse flow modulator (PFM) was developed in this work. PFM working parameters have been always optimized to allow combinations of columns with different sizes. Optimized PFM allows application of columns with 10-60 m length and 0.15-0.25 mm internal diameters for the first dimensions and with 1-10 m length and 0.25-0.32 mm internal diameters for the second dimension. For demonstration reasons, analyses of complex real samples, such as essential oils, oil derivatives and biological samples, were performed. PFM was compared with the commercial cryofocusation modulator Zoex for the selected column set and one sample (a mixture of volatile solvents) on a gas chromatograph equipped with both modulators. The average repeatability of retention times, expressed as a relative standard deviation, was approximately 2.0 % for PFM (cryofocusation about 0.5 %) and of the peak areas was approximately 3.5 %...
Polymethacrylate monolithic columns in capillary liquid chromatography
Grafnetter, Jan ; Coufal, Pavel (advisor) ; Pacáková, Věra (referee) ; Ventura, Karel (referee) ; Sýkora, David (referee)
3 Conclusions This Thesis gives chromatographic and structural characteristics of the butyl methacrylate monolithic columns prepared for the capillary liquid chromatography. Results of this Thesis clearly demonstrate the possibility of preparation of capillary monolithic columns with a good repeatability of the principal chromatographic parameters. A completely new technique for preparation of the monolithic columns for use in the on-column detection mode was introduced. Different photometric detection modes were applied to monolithic capillary columns in CLC. The advantages and disadvantages of the on-column detection mode in comparison to the additional detection capillary were studied and described. It was shown that the best separation and the most sensitive quantification in the short analysis time could be reached by using the monolithic columns with detection window placed directry on the separation capillary, just after the stationary phase or within the monolith. The attempts leading to preparation of chiral monolithic stationary phases, which would allow enantioseparation of selected chiral analýes' were not totally successful. No time was left to find the suitable chromatographic conditions for enantioseparations. \ I
Analysis and Biochemistry of Less Current Steroids - Neuroactive Steroids and Their Sulfates
Včeláková, Helena ; Hill, Martin (advisor) ; Ventura, Karel (referee) ; Meloun, Milan (referee)
Disertation work brings new findings in the field ofbiochemistry and analysis of neuroactive steroids. The pubrications invorved to the dissertation work dear with biochemicar anarysis of neuroactive steroids and its apprication in biomedicine. Some endogenous steroids can act as efficient neuromodurators' These substances are known as neuroactive steroids' If they are synthesized directly in the central nervous system, they have been named the neurosteroids (Schreiber 1980; corpechot, Rober et ar. rggl). some of the neuroactive steroids act as neuroactivators, the others are neuroinhibitors (Kimonides, Khatibi et al. l99g; Kaasik, Kalda et al. 2001; Lockhart, Warner et al. 2002). The neuroactive steroids operate usually as modulators of membrane receptors (GABA_ receptors and NMDA_receptors) responsible for the permeability of ion channels in neuronal cells. Generally, while physiologic functions and pharmacokinetics of endogenous neuroactive steroids studied on animals was investigated (Wang, Wahlstrom et al. 1997; Norberg, Backstrom et al. 19gg), the number of studies concerning neuroactive steroids in human body fluids and tissues in connection with physiology is insufficient (Bicikova, Tallova et al. 2000; Strohle, Romeo et al. 2003). The main problem is probably laboriousness of corresponding...
Comprehensive analysis of warning and defense compounds of true bugs by high-performance separation methods
Krajíček, Jan ; Bosáková, Zuzana (advisor) ; Feltl, Ladislav (referee) ; Ventura, Karel (referee)
Insects have developed many strategies of defence against predators in the course of evolution. The evolutionarily oldest and most widely used type of defence is chemical defence, followed by acoustic or optical defence. However, many species of insects use simultaneously multiple types of warning signals, which affect different sensory receptors of the given predator. Such a complex method of warning signals is called multimodal method. It may consist of a combination of simultaneous chemical and optical signals, or a combination of acoustic and optical signalling. The combination of chemical and optical signalling used against a predator is probably the most common form of multimodal signalling. The presented work deals with the analysis of biologically active substances, which participate in the defence mechanisms of a widespread species of insects - true bugs (Heteroptera). Pterin derivatives represent a large group of natural compounds derived from pteridin, bicyclic heterocycle, and they are found in virtually all living organisms from bacteria to vertebrates. In insects, they primarily serve as pigments, resulting for example in striking coloration of cuticles of Heteroptera. The first part of the dissertation was focused on identification and quantification of pterin derivatives in cuticles...
Toxicity of Organic Mixtures
Reitmajer, Josef ; Feltl, Ladislav (advisor) ; Čabala, Radomír (referee) ; Ventura, Karel (referee) ; Mejstřík, Viktor (referee)
6. CONCLUSION The aim of this study was to test additiviý of chemical compounds in distribution process between two phases and to compare distribution coefficients K-;^ for different molar ratio of mixture with acute toxicity index EC50 gained on oligochaeta Tubifex tubifex. Mixtures of organic solvents ethanol, benzene, aniline and nitrobenzene were studied. Deviations from additivity were found for distribution coefficients of all tested mixtures. The most significant deviation exhibited benzene - ethanol mixture. The lowest deviations were observed for mixture ethanol - aniline. The results obtained indicate that the partition coefficient K.;* behave similarly as acute toxiciý. Definitely it is for benzene - ethanol mixture. It is possible to suppose that this parameter might be used for estimation of changes in acute toxicity of mixtures. The aim of the second part of the thesis was to study how distribution of chemicals changes with concentration and composition of mixture. Variations in distribution of mixture components beťween gaseous and aqueous phase were found. The highest deviations were found for benzene - ethanol and benzene - eniline mixtures. No deviation was found for mixture aniline - nitrobenzene. Deviations were not as significant as in first part of study. Dependences of distribution...
Study of the Selected Types of Sulphur Compounds in Beer and Brewing Materials
Mikulíková, Renata ; Ventura, Karel (referee) ; Ventura, Karel (referee) ; Čáslavský, Josef (referee) ; Márová, Ivana (advisor)
Much attention has been recently devoted to sensorially active substances affecting beer quality in the Czech Republic and worldwide. Among them, the heterocyclic and sulphur containing compounds play an important role, some of them with high sensorial activity even in extremely low concentrations. Trace amounts of these compounds, which can be frequently found in foods, participate in formation of their aroma and this effect can be generally evaluated as favorable However, in malt or beer it is true only to a limited extent and the presence of heterocyclic and sulphur containing compounds are in this respect assessed rather unfavorably. The aim of the present study was to provide a survey about of problems in the field of sulphur containing compounds in barley, malt and beer, to describe metabolic paths leading to their formation and to verify experimentally possibilities of their determination using modern analytical methods. Sulphur-containing amino acids are a natural part of barley, malt and beer and are precursors of the origin of volatile sulphur substances. The most frequently occurring sulphur amino acids, metionine, cysteine and homocysteine, were selected for analytical monitoring. The method of gas chromatography was used to determine sulphur-containing amino acids in barley, malt and beer. Prior to the analysis, sulphur-containing amino acids were derived and volatile N(O,S)-ethoxycarbonyl propyl esters were formed; they were subsequently analyzed using the gas chromatography with mass detector (GC/ MSD) and the gas chromatography with flame photo detector (GC/ FPD). Direct analysis of sulphur volatile substances is possible only rarely as they are found in the analyzed matrices (malt, beer) only in very low concentrations ( g/kg,l - ng/kg,l). Before the analysis, the analytes must be extracted from the matrix and concentrated. The modern analytical methods SPME (Solid Phase Micro Extraction), SPDE (Solid Phase Dynamic Extraction) and TDAS (Thermal Desorption Autosampler) were experimentally compared for the extraction and subsequent concentration of sulphur volatile substances. The method of gas chromatography with flame photo detector was used to determine sulphur volatile substances. Following volatile sulphur substances were monitored: dimethyl sulphide, dimethyl disulphide, dimethyl trisulphide, carbon disulphide, ethyl sulphide, diethyl disulphide, methionol, 3-methylthiophen, ethyl thioacetate, 2-methyl-1-buthanthiol. Only metionine was detected in significant amounts in the barley samples analyzed. Not only content but also dependence on a variety and locality were studied. Further, changes in methionine, cysteine and PDMS content during malting were followed. Results proved a significant decline in these substances content depending on the kilning temperature. Three types of fibers were tested for the analyses of the selected volatile sulphur substances in beer in the SPME method. PEG - a fiber with stationary phase Carbowax, PDMS - a fiber with stationary phase polydimethylsiloxan and a combined fiber CAR/PDMS - Carboxen and polydimethylsiloxan. Carbon disulphide, methionol, dimethyl sulphide, 3-methylthiophen and diethyl disulphide were detected with this method. Content of the other analyzed volatile sulphur substances was below the limit of detection. Further was tested usage the SPDE and TDAS methods. Both methods appear to be the suitable for the determination of volatile sulphur substances in beer.

National Repository of Grey Literature : 13 records found   1 - 10next  jump to record:
Interested in being notified about new results for this query?
Subscribe to the RSS feed.