National Repository of Grey Literature 56 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
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

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