National Repository of Grey Literature 58 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Analysis of unstable complexes for study of enzymatic methylation of arsenic
Albrecht, Michal ; Petry-Podgórska, Inga (advisor) ; Červený, Václav (referee)
The main aim of this thesis was the development of conjugation of existing methods for analysis of arsenic-glutathione complexes (As-GS complexes) together with simple arsenic species (iAs, MMAs, DMAs) during simple run. The basic technique for analysis of As-GS complexes was the HPLC-ICP-MS method with a reverse phase separation column (C18). The separation problem of simple species has been overcome by extending of system by postcolumn hydride generation with cryotrapping system (HG-CT). The resulting HPLC/HG-CT-ICP-MS system provides a complex analysis of all the above-mentioned analytes. According to the currently available resources, it is an innovative system, where for the first time all the simple arsenic species (iAs, MMAs, DMAs) and the As-GS complexes were separated. Under the given conditions, the detection limit for the As-GS complexes of 1.9 pg cm-3 in the RP-HPLC-ICP-MS system (a quantification limit of 6.5 pg cm-3 ) was achieved at a sensitivity of 468 CPS s pg-1 . The HG-CT-ICP-MS system provided a detection limit for iAs of 1.2 pg cm-3 at a sensitivity of 1121 CPS s pg-1 , for MMAs of 0.043 pg cm-3 at a sensitivity of 895 CPS s pg-1 and for DMAs of 0.076 at a sensitivity of 926 CPS s pg-1 . This method was applied to achieve another aim, studying the pathways of enzymatic...
UV-photochemical generation of cadmium volatile compounds with atomic spectrometric detection
Horová, Kateřina ; Nováková, Eliška (advisor) ; Červený, Václav (referee)
The aim of this master's thesis has been to develop and optimize the method of UV- photochemical vapor generation of cadmium volatile compounds for atomic fluorescence spectrometry. Two configurations with different materials wrapped around the low-pressure mercury vapor lamp were tested. I experimentally determined optimal conditions for both systems; the optimalized parametres included selection of photochemical reagent and its concentration, flow rate of liquids and gases, and the lenghth of the reaction coil. After finding the optimal parametres I determined the figures of merit of the method. I found from the measured data that UV-photoreactor with the quartz capillary provided lower limits of detection and thus was more suitable for generation of cadmium volatile compounds. With this arrangement and using the ferrous sulphate heptahydrate as the chemical modifier I obtained limit of detection 2,0 µg·l-1 , limit of determination 7,0 µg·l-1 , linear dynamic rate LOD-50 µg·l-1 and repeatibility 0,35 %. I also carried out the interference study in my thesis and determined the generation effeciency of cadmium volatile compounds. The interference study shows the influence of mineral acids (HCl, H2SO4, HNO3), their salts (NaNO2, NaNO3) and transition metals (Co, Ni, Cu). Based on literature review I also...
Speciation analysis of arsenic and mercury using postcolumn generation of their volatile compounds for needs of atomic spectroscopic methods
Linhart, Ondřej ; Červený, Václav (advisor) ; Spěváčková, Věra (referee) ; Šíma, Jan (referee)
The presented dissertation thesis deals with the use of UV-photochemical generation of volatile compounds (UV-PVG) as a derivatization technique for the combination of high-performance liquid chromatography (HPLC) and atomic absorption spectrometry (AAS) detection. Two model elements arsenic and mercury and their compounds were selected for the speciation analysis. The work was divided into several parts that follow. In the first part of the research, the apparatus for the UV-photochemical generation of the volatile mercury compounds and their detection with a new continuum source and high-resolution atomic absorption spectrometer (HR-CS AAS) with an externally heated detection tube was constructed. The analytical method was adapted for use with atomic fluorescence detection with the aim to improve sensitivity of the determination. Furthermore, apparatus for the electrochemical generation of cold mercury vapor with AAS detection was built. The construction of the apparatus was followed by optimization of the reaction conditions (concentration and flow of electrochemical reagents: sulfuric and hydrochloric acid, mobile phase, carrier medium, flow rate of the carrier gas and localization of its introduction), determination of the analytical figures of merit, and comparation of the methods. Both...
Comparison of various approaches to determination of antimony by atomic fluorescence spectrometry
Adámková, Dominika ; Červený, Václav (advisor) ; Hraníček, Jakub (referee)
Bakalářská práce se zabývá porovnáním tří způsobů generování těkavých sloučenin pro stanovení antimonitých a antimoničných iontů pomocí atomové fluorescenční spektrometrie. Pro porovnání jednotlivých stanovení byly vždy nejprve nalezeny nejvhodnější experimentální podmínky. Protože je chemické generování považováno za nejúčinnější v porovnání s ostatními typy generování a je také nejčastěji používáno, bylo charakterizováno jako první. Bylo dosaženo limitu detekce 0,12 ppb pro Sb3+ a 0,28 ppb pro Sb5+ . Ovšem nejvyšší citlivosti a nejnižšího limitu detekce bylo dosaženo pro elektrochemické generování hydridu antimonu. Metoda EcHG byla přibližně 4×citlivější než technika CHG. Dosaženo bylo limitu detekce 9 ppt pro Sb3+ a 45 ppt pro Sb5+ . Nejnižší citlivost byla získána podle předpokladu při UV - fotochemickém generování, a to přibližně 9×nižší oproti elektrochemickému generování. Celkově stanovení antimonitých iontů bylo nejméně 4×citlivější než stanovení antimoničných iontů. Podle tvaru píku usuzuji, že tvorba těkavé sloučeniny probíhala u všech způsobů generování v případě Sb5+ pomaleji než u Sb3+ . Klíčová slova Atomová fluorescenční spektrometrie, antimon, generování těkavých sloučenin, chemické generování těkavých sloučenin, UV - fotochemické generování těkavých sloučenin, elektrochemické...
Comparison of selenium extraction efficiency from food supplements
Molnárová, Lucia ; Hraníček, Jakub (advisor) ; Červený, Václav (referee)
The aim of this bachelor thesis was comparison of selenium extraction efficiency from food supplements which contain various declared forms of selenium. The method of atomic absorption spectrometry with flame atomization was used to determine the efficiency of the extraction. The first step for the determination of selenium in four real samples was the experimental finding of optimal conditions for selenium determination by flame AAS technique. Optimized parameters included the flame composition, the fuel flow rate, the angle of burner rotation, the horizontal burner position and the spectral range. During the testing the flame composition, higher responses were measured by using air as an oxidant, and therefore acetylene-air flame was used to other optimize and measure real samples. After optimization of the conditions, the calibration dependence was determined and the basic characteristics of the measurements were calculated. The detection limit and determination repeatability, sensitivity and operating range were determined for selenium determination. The detection limit was 0.12 mg dm-3 . The real samples of the food supplement tablets were mechanically homogenized and transferred to aqueous solutions, which were subsequently analyzed by the optimal conditions. The highest extraction efficiency...
Determination of arsenic species in seafood reference materials by ICP-MS with hydride generation and cryotrapping
Pokorná, Nikola ; Matoušek, Tomáš (advisor) ; Červený, Václav (referee)
The aim of this work was to determine chemical species of arsenic in sea originating certified reference materials. Measurements were done using method of hydride generation. Hydrides were preconcentrated in liquid nitrogen cooled tube and detected using inductively coupled plasma mass spectrometry. During the testing of the method, mutual conversion of arsenic species was observed for inorganic arsenic, monomethyl arsenic and dimethylarsenic. Further study revealed that with presence of matrix and hydrogen peroxide, demethylation occured only in hydride generation phase, not during extraction. Dissociation of hydrogen peroxide in extracts was verified using catalase. End of the demethylation process was proved using measurement with addition of arsenic species standards. The newly invented procedure was used to determine arsenic species in reference materials with sufficient accuracy. Final results are compatible with results from different method, and already published results as well. Key words: speciation analysis, arsenic, hydride generation, seafood, inductively coupled plasma mass spectrometry

National Repository of Grey Literature : 58 records found   1 - 10nextend  jump to record:
Interested in being notified about new results for this query?
Subscribe to the RSS feed.