National Repository of Grey Literature 106 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Generation of volatile zinc chelates from aqueous matrix
Kračmarová, Aneta ; Nováková, Eliška (advisor) ; Červený, Václav (referee)
The topic of this work was optimization of the conditions for the generation of volatile zinc chelates. The aim was to develop an alternative method for generating volatile Zn speciates to its reduction by sodium tetrahydridoborate. Detection was carried out by atomic absorption spectrometry. Optimization of the conditions of the chelation reaction itself included the selection of a suitable chelating agent and appropriate modifiers, pH adjustment, suitable reagent and carrier gas flow rates, and appropriate apparatus arrangement. The following method characteristics were obtained under optimal conditions: LOD 1.55 mg L-1 , LOQ 5.17 mg L-1 and sensitivity 0.245 s L mg-1 . The repeatability was 13,7 %. The addition of modifiers was then tested to increase the efficiency of generation of volatile zinc chelates. Potential modifiers included transition metals, organic solvents, heterocyclic organic compounds, compounds from the carbamate group and surfactants. The heterocyclic 1,10-phenanthroline and the carbamate NaPDC were included in the optimal conditions because without them it was not possible to distinguish the signal from noise. Acetonitrile proved to be the most effective modifier, increasing the efficiency to 1547 %. With the addition of acetonitrile, the LOD decreased to 0.191 mg L-1 , the...
The effect of selected compounds on determination of antimony by atomic fluorescence spectrometry with UV-photochemical generation of volatile compounds
Jelínková, Klára ; Červený, Václav (advisor) ; Nováková, Eliška (referee)
5 Abstract This bachelor thesis is focused on the investigation of the influence of selected chemical individuals on the determination of antimony by UV-photochemical generation of volatile compounds with atomic fluorescence spectrometry detection (UV-PVG-AFS). Antimony, as a toxic semimetal occurring mainly in the trivalent and pentavalent oxidation state, plays an important role in many industries. Its determination is of importance not only from the point of view of analytical chemistry but also for monitoring of its environmental effects and for human health. For the interference studies with Sb5+ , the inorganic ions Br− , Cr2O7 2− , I− , CO3 2− , K+ , Cr3+ , Cd2+ , Co2+ , Cu2+ , Ni2+ , Na+ , Zn2+ , the organic solvents acetonitrile, ethanol and methanol, as well as the extraction reagents L-cysteine and 2-mercaptoethanol were chosen. Br− , Cr2O7 2− , I− , CO3 2− , K+ , Cr3+ , Cd2+ , Na+ and Zn2+ were chosen as possible interferents in the determination of Sb3+ . Solutions of the interferents were prepared in a medium of acetic acid (35%v/v) and 50 g l−1 Sb3+ or Sb5+ . The detection limit of the determination of Sb3+ in the flow injection mode analysis was 3.7 g l−1 for peak area and 1.9 g l−1 for peak height evaluation. For Sb5+ determination, the detection limit was 3.6 g l−1 for peak area and...
Optimization of the operational temperature of photoluminescence sensor field for detection of linear alcohols
Pokorný, Matěj ; Dian, Juraj (advisor) ; Červený, Václav (referee)
Chemical sensors are used to detect the presence of chemical substances using various physical quantities. Porous silicon, prepared by electrochemically etching the surface of crystalline silicon with a mixture of hydrofluoric acid and ethanol under appropriate conditions, is a porous material that contains nanocrystalline forms of silicon. Nanocrystalline silicon exhibits intense photoluminescence properties at room temperature, which strongly depend on the presence of chemical substances in its surroundings. The photoluminescence intensity of porous silicon is generally quenched in the presence of the analyte. The photoluminescence sensor response to the substances to be determined depends mainly on the concentration of the substance in question, but also on the operating conditions. Most critical is the operating temperature, which fundamentally affects the intensity of photoluminescence and the rate of sensor response when the analyte is added or removed from the system. The aim of this bachelor thesis was the preparation of porous silicon samples and their characterization by infrared (FTIR) and photoluminescence spectroscopy. These samples were tested as sensor elements of a photoluminescence sensor array for the detection of ethanol linear alcohol vapor. The main objective of the bachelor...
Compatibility of determination of antimony by UV-photochemical generation of volatile compounds and atomic fluorescence spectrometry with potential matrix components
Klečková, Adéla ; Červený, Václav (advisor) ; Nováková, Eliška (referee)
The root of this bachelor work is UV-photochemical generation (UV-PVG) of volatile substances of antimony. Problematics, with which we deal, are potential interferences, which can affect measurement. As model interferents when considering future speciation analysis of antimony using HPLC-UV-PVG-AFS were chosen acetonitrile, methanol, ethanol, L-cysteine and 2-mercaptoethanol. Detection was progressed using atomic fluorescence spectrometry (AFS). L-cysteine muffled the response. Methanol and ethanol were behaving alike. They were increasing and lowering the peaks in waves, when only at the highest concentration they completely disappeared. Acetonitrile was proved to be the most interesting one thanks to its specifical behaviour, which started to show off in higher concentration. 2-mercaptoethanol had in smaller amount similar interference properties as acetonitrile.
Determination of elements in human hair
Gazda, Vojtěch ; Nováková, Eliška (advisor) ; Červený, Václav (referee)
The bachelor thesis is focused on the determination of selected elements in human hair. For the determination of 13 samples, a procedure for their digestion with concentrated HNO3 and elemental analysis using inductively coupled plasma mass spectrometry ICP-MS was proposed. The results were compared with other sources, if the cited works reported the geographical origin of the sample, the differences in our population are compared with the population in another country. The concentrations of heavy metals that were determined were not particularly different from the others, with the exception of Pb, here it was found that in the area where the samples were taken the concentration of Pb in hair is low and this finding shows that the people from whom the samples come are not exposed to Pb from the environment and work environment and from food and water. Subsequently, the samples were found to contain more Mg, Sr, Ni, Ba and Au compared to others reported in the literature. The next objective was to determine if the concentrations differed between the sexes. Men were found to have higher concentrations of K than women, while women's hair was found to contain almost 12 times more Ca and Mg than men's hair. Therefore, in order to prove whether there was a statistical difference between the...
Optical characterization of supramolecular complexes of selected organic fluorophores with cyclodextrins
Haiklová, Simona ; Dian, Juraj (advisor) ; Červený, Václav (referee)
The content of this thesis is the optical characterization and determination of the strength of supramolecular interaction of selected organic fluorophores and cyclodextrins (CD) using the stability constant with optical methods: UV-Vis absorption and fluorescence. Two series of fluorophores differed in the presence of groups with two positive charges, and two types of cyclodextrins (-CD a -CD) with different cavity sizes were chosen for the study. Fluorophores with charged end groups can be efficiently bound by electrostatic interaction on solid surfaces of suitable chemical composition or thin films with an excess of negative charge and thus immobilized by a very strong interaction on a given support. These prepared surfaces or layers can then be used for the optical detection of chemical substances. The aim of this work was to determine the influence of cyclodextrin cavity size, the presence of a charged anchor, and solution pH on the supramolecular interaction of the studied systems and evaluate the application possibilities of the studied systems for optical chemosensors. In the presented thesis, the change in optical absorption and fluorescence intensity of four pairs of fluorophores: PRODAN, RhB, RhB-Si, DANSA, and their derivatives with a charged anchor was studied during supramolecular...
Determination of Mercury in Hair by Atomic Fluorescence Spectrometry
Šandlová, Petra ; Červený, Václav (advisor) ; Hraníček, Jakub (referee)
The functionality of PS Analytical's Millenium Merlin Satellite external module to the PSA Millenium Excalibur atomic fluorescence spectrometer has been demonstrated on real samples. Hair was selected as real samples. In the first part, several extraction procedures were tested to obtain the highest response. The best results were obtained by the extraction method with TMAH and HCl in FIA-UV-PVG- AFS mode. In the next part, an attempt was made to optimize the conditions for the separation of mercury speciation, namely Hg2+ and MetHg. The optimized parameters were: the percentage of organic component in the mobile phase, the pH of the mobile phase, the flow rate of the added mobile phase per column, and the flow rate of the added 0.050M HCl per column. After this stage, 3 more extraction procedures were tested: extraction using L-cysteine with HCl, extraction using PDTC and extraction using DEDTC. However, none of the extraction procedures was better than the extraction method with TMAH and HCl. Despite the optimization of the method, the speciation of Hg in the hair samples failed because the chromatograms obtained did not match (even in retention times) those obtained for the mixture of standards with the mobile phase extraction reagents. Subsequently, the conditions for the determination of total...
Porous silicon based optical sensors of chemical species for gas phase
Liška, Jiří ; Dian, Juraj (advisor) ; Červený, Václav (referee)
Title: Porous silicon-based optical sensors of chemical species for gas phase Author: Bc. Jiří Liška Department: Department of Inorganic Chemistry Supervisor: doc. RNDr. Juraj Dian, CSc. Abstract: Porous silicon is a nanostructured material, which is a suitable material for che- mical sensors due to its optical properties, especially photoluminescence and its quenching depending on the chemicals in the environment. Optical sensors based on porous silicon are the most studied group of sensors and have been successfully used for the detection of chemicals in both liquid and gas phases. In addition, the surface of porous silicon can be modified by a number of techniques, thereby modifying the recognition properties. In the case of combining multiple sensor elements of different properties, it is possible to measure multiple responses in the photoluminescent sensor array. The objectives of this thesis are: 1. Extension of electrochemical characterisation of initial silicon substrates using vol- tammetric techniques under different lighting conditions during the experiment, preparation of porous silicon samples from different types of crystalline silicon sub- strates (p-type, n-type), crystallographic orientation and doping degree. 2. Functionalisation of porous silicon surface with new chemical compounds by...
Application of a commercial multimode sample introduction system as a generator of volatile compounds
Hadbavníková, Alexandra ; Nováková, Eliška (advisor) ; Červený, Václav (referee)
EN The main goal of this thesis was the determination of zinc using a commercial multimode sample introduction system (MSIS) as a generator of volatile compounds with inductively coupled plasma mass spectrometer as detector. The generation of volatile compounds took place using sodium borohydride in an acid environment. In the first step of the experiment, the following parameters affecting the generation of volatile compounds were optimized: acid selection, acid concentration, sodium hydroxide concentration, mass concentration of sodium borohydride, mass concentration of 8-hydroxyquinoline, volume of the injection loop and flow rates of sample, carrier gas and hydrogen. Subsequently, figures of merit of the method were determined under optimal conditions. The limit of detection was 2.8 μg·dm-3 and the limit of quantification was 9.3 μg·dm-3 . Generation efficiency of the volatile zinc compound was determined as 3.7 %, which is the highest efficiency yet achieved for this element and generation system in this laboratory. Interference studies did not demonstrate the ability of any of the tested hydride-forming or transition elements to act as a modifier increasing the generation efficiency, but at the same time, none of the investigated elements proved to be a significant interferent. Key words...

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