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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.
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Multicomponental Preconcentration of As, Sb, Se and Te on Modified Silica, Their Determination by ICP-AES (ICP-MS) and Application for Waters
Urbánková, Kristýna ; Řehůřková, Irena (referee) ; Kanický, Viktor (referee) ; Ventura, Karel (referee) ; Sommer, Lumír (advisor)
The determination of inorganic speciations of arsenic, antimony, selenium and tellurium in natural waters demands often separation and preconcentration. Solid phase extraction is a very effective method for these purposes. In this paper the separation and preconcentration of these microelements is realised on the basis of modified silica Separon SGX C18, SGX C8, SGX CN, SGX NH2, SGX Phenyl and strongly basic anion Exchanger SGX AX. The sorption was provided in the presence of cationic surfactants such as benzyldimethyl dodecylammonium bromide (Ajatin), benzyldimethyltetradecylammonium chloride (Zephyramine), 1-ethoxycarbonylpentadecyltrimetrhylammonium bromide (Septonex) and selected complexing agents 4-(2-pyridylazo)resorcinol (PAR), 8-hydroxyquinoline-5-sulphonic acide (8-HQS), 1,2-dihydroxybenzene (PYR), amonium 1-pyrrolidinecarbodithioate (APDC), sodium diethyldithiocarbamate (DTC) or thiourea(Thur). The interactions of the formed ion associate with the sorbent shows a complicated character which has not been cleared as yet. The previous conditioning of the sorbent plays an outstanding role. Thus, the sorption efficiency was studied in the presence and absence of surfactant and of selected organic complexing agents. Moreover, the influence of pH of the sorbed solution as well as the speed and the volume of the solution running through the sorbent and the type and volume of the eluent on the resulting sorption efficiency was evaluated. The sorption was successfully carried out from 50-1000 ml of solution which allows the 100 fold increase of the preconcentration factor and the determination of the microelements in g.l-1 instead of mg.l-1 by using the common ICP-AES. The influence of macroelements occurring in waters as well as B, Be, Bi, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sr, Ti, V and Zn in comparable concentrations involve less than 5% error. After the quantitative elution of microelements, the organic solvents were evaporated under IR lamps prior to the determination by ICP-AES and |ICP-MS. The conditions for the direct determination of arsenic, antimony, selenium and tellurium in g.l-1 with ICP-MS were also described in detail in the absence and presence of internal standards Ge and Bi. However, even in this case the preconcentration on silica in the presence of surfactant and selected organic complexants was also tested. When the sorption was followed from 500 ml a 50 fold enrichment factor is reached and the sensitivity for the microelements is improved. The direct determination and the sorption of microelements were applied on synthetic and real waters (dirinking, surface, mineral and sea waters). Instrumental and practical detection limits for various water samples were evaluated according to IUPAC. The results from 1000 ml solution of real waters after sorption on modified silica and the final determination of microelements with ICP-AES were compared with those from ICP-MS without sorption using the method of standards addition in the presence of suitable internal standards. By comparison of results for synthetic and real water samples the error of the determination of microelements was evaluated.
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Separation of Azaarenes by High Performance Liguid Chromatography
Kočí, Kamila ; Friedl, Zdeněk (referee) ; Večeřa, Zbyněk (referee) ; Ventura, Karel (referee) ; Šimek, Zdeněk (advisor)
Under the framework of this PhD project, a study on chromatographic behaviour of selected azaarenes on octadecylsilica stationary phases during their separation by reversed phase liquid chromatography was developed. The main goal was aimed at an application of the basic RPLC principles on the retention behaviour of azaarenes including the effects such as peak tailing, peak broadening, irreproducible retention or strong retention on a stationary phase. This study was particularly focused on basic azaarenes, also called acridines, which belong to a group of persistent organic pollutants providing mutagenic and/or carcinogenic activity. The retention patterns were studied on a group of eight acridines that are often present in environmental samples polluted with polycyclic aromatic compounds. The mixture of acridines was separated under isocratic elution conditions on three octadecylsilica stationary phases using two different binary mixtures as a mobile phase. Evaluation of the surface properties of the selected stationary phases was firstly performed, followed by the separation experiments. The structure of the experiments was designed to evaluate the effect of three different factors on the retention behaviour of acridines: properties of a stationary phase, composition of a mobile phase and physical-chemical properties of acridines. The treatment of the results was based on the capacity factor values providing the best fitting and repeatability of data, but other parameters that evaluate thermodynamic and kinetic aspects of the separation process were also given. Simple correlations between the three factors and a character of retention mechanism of acridines on the given separation system were found. Application of this knowledge simplifies an optimisation process and helps to solve common separation problems for acridines, but also for other basic analytes displaying similar physical-chemical properties (Mr and pKa).
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Determination of Natural Compounds in Select Plant Materials and Less Obvious Kinds of Fruit
Hohnová, Barbora ; Márová, Ivana (referee) ; Ventura, Karel (referee) ; Omelková, Jiřina (advisor)
Flavonoids are natural compounds widely distributed in plant kingdom. They are inseparable from human diet because they showed a protective effect against cancer, stroke and coronary heart diseases related to their antioxidant properties. Therefore, rapid and efficient extraction procedure prior to chromatographic analysis is required. The liquid extraction at elevated temperature and pressure – Pressurized fluid extraction (PFE) and Pressurized hot water extraction (PHWE), present fast, effective and environmentally friendly extraction methods for the determination of flavonoids in plant materials. PFE and PHWE followed by reversed phase high-performance liquid chromatography with UV-visible detection have been utilized for the determination of a group of flavonoids (rutin, myricetin, quercetin, luteolin, apigenin and kaempferol) in the leaves and berries of less common plants. The matrices were extracted by methanol, ethanol and water at higher temperature 40-120 oC and pressure 15 MPa during 15 minutes. The obtained results were compared with conventional Soxhlet extraction and ultrasound-assisted extraction, the same solvents were used. The most effective extraction of selected flavonoids was achieved by PHWE. PFE showed the extraction yields comparable to those of the Soxhlet extraction, and the lowest extraction power was displayed by ultrasound-assisted extraction.
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Modern extraction techniques in connection with HPLC for analysis of contaminants
Kholová, Aneta ; Šatínský, Dalibor (advisor) ; Ventura, Karel (referee) ; Malíř, František (referee)
Charles University, Faculty of Pharmacy in Hradec Králové Training Workplace Department of Analytical Chemistry Doctoral Degree Program Bioanalytical Methods Candidate Mgr. Kholová Aneta Supervisor prof. RNDr. Dalibor Šatínský, Ph.D. Advisor PharmDr. Ivona Lhotská, Ph.D. Title of Doctoral Thesis Modern extraction techniques in connection with HPLC for analysis of contaminants A compilation of six publications is presented in this dissertation thesis. The work focuses on applying and comparing extraction sorbents to analyze contaminating substances in food and food supplements. The main aim of this thesis was to present micro and nanofibers as suitable extraction sorbents for use in analytical chemistry. For this purpose, the fibers were compared with other, mostly commercial, extraction sorbents suitable for the type of matrix tested. All experiments were carried out in the on-line connection of the extraction sorbent through the selection valve with the analytical column in the chromatographic system. A crucial part was also the use of the extraction properties of nanofibers for the analysis of real-life samples. In the first part, the extraction efficiency was studied on liquid matrices, where no need for complex matrix purification was required. The main aim was sufficient retention and...
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Modern extraction techniques in connection with HPLC for analysis of contaminants
Kholová, Aneta ; Šatínský, Dalibor (advisor) ; Ventura, Karel (referee) ; Malíř, František (referee)
Charles University, Faculty of Pharmacy in Hradec Králové Training Workplace Department of Analytical Chemistry Doctoral Degree Program Bioanalytical Methods Candidate Mgr. Kholová Aneta Supervisor prof. RNDr. Dalibor Šatínský, Ph.D. Advisor PharmDr. Ivona Lhotská, Ph.D. Title of Doctoral Thesis Modern extraction techniques in connection with HPLC for analysis of contaminants A compilation of six publications is presented in this dissertation thesis. The work focuses on applying and comparing extraction sorbents to analyze contaminating substances in food and food supplements. The main aim of this thesis was to present micro and nanofibers as suitable extraction sorbents for use in analytical chemistry. For this purpose, the fibers were compared with other, mostly commercial, extraction sorbents suitable for the type of matrix tested. All experiments were carried out in the on-line connection of the extraction sorbent through the selection valve with the analytical column in the chromatographic system. A crucial part was also the use of the extraction properties of nanofibers for the analysis of real-life samples. In the first part, the extraction efficiency was studied on liquid matrices, where no need for complex matrix purification was required. The main aim was sufficient retention and...
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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...
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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...
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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
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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...
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