High-valent transition metal-oxo intermediates are of fundamental importance because of their central role as active oxidizing species in enzymatic and synthetic catalytic oxidations. Many transition metal catalysts have been extensively studied as models of the ubiquitous cytochrome P450 enzymes to probe the sophisticated oxygen atom transfer mechanism as well as to invent enzyme-like oxidation catalysts. In this work, photolysis of highly photo-labile corrole-manganese(IV) bromates or nitrites by visible light was studied in two corrole systems with different electronic environments. The corrole systems under studied include 5,10,15- tris(pentafluorophenyl)corrole (TPFC) and 5,10,15-triphenylcorrole (TPC). As observed in both systems, homolytic cleavage of O-Br or O-N bonds in the ligands resulted in one-electron photo-oxidation to generate corrrole-manganese(V)-oxo species, as determined by their distinct UV-vis spectra and kinetic behaviors. The kinetic of oxygen atom transfer (OAT) reactions with various substrates by these photogenerated [MnV(Cor)(O)] were studied in CH3CN and CH2Cl2 solutions. [MnV(Cor)(O)] exhibits remarkable solvent and ligand effects on its reactivity and spectral behaviors. In the more electron-deficient TPFC system and in the polar solvent CH3CN, MnV-oxo corrole returned MnIII corrole in the end of oxidation reaction. However, in the less polar solvent CH2Cl2 or in the less electron-deficient TPC systems, MnIV product was formed instead of MnIII. With the same substrates and in the same solvent, the order of reactivity of MnV-oxo corrole was inverted as TPC > TPFC. The spectra and kinetic results are rationalized by a multiple oxidation model, where the electron-demand MnVoxo species may serve as direct two-electron oxidation for oxygen atom transfer reactions; and less electron-demand systems undergo a disproportionation reaction to form a putative manganese(VI)-oxo corrole as the true oxidant. The choice of pathways is strongly dependent on the nature of the solvent and corrole ligand. Furthermore, porphyrin-manganese(V)-oxo were produced in organic solvents by visible light irradiation of the corresponding porphyrin-manganese(III) nitrite complexes. The porphyrin systems studied were 5,10,15,20-tetrakispentafluoro phenylporphyrin (TPFPP), 5,10,15,20-tetrakis(2,6-difluorophenyl)porphyrin (TDFPP) and 5,10,15,20-tetrakis(2,6-dichlorophenyl)-porphyrin (TDCPP). Heterolytic cleavage of O-N bond of nitrite ligand results in two-electrons photo-oxidation. Under visible light irradiation, MnV-oxo porphyrins quickly returned to MnIII product. However, in absence of light, MnIV-oxo species were formed, as determined by their distinct UV-vis spectra, which permitted direct kinetic studies. The apparent rate constants for reaction of [MnIV(Por)(O)] species show inverted reactivity order with (TPFPP) < (TDFPP) < (TDCPP) in reactions with ethylbenzene. A model for oxidation under catalytic condition was presented.

This thesis deals with optimization of conditions of photochemical generation of volatile species of nickel for atomic absorption spectrometry. The volatile species of nickel were generated in the flow arrangement, when sample was injected to a stream of a reaction medium. Either formic acid was used as the reaction medium or formic acid with the addition of formate anions. Two types of a generator were tested, a generator with a PTFE tube wrapped around a mercury UV lamp and a high efficiency generator with an inside channel. At the same time, two types of a gas-liquid separator were tested. Diffusion flame was used as an atomizer due to its high robustness. Quartz atomizer didn't provide higher sensitivity and measurements had worse repeatability. All the parameters affecting atomization in the diffusion flame were optimized (flow rates and composition of gases, observation height). In the next section, conditions of generation (irradiation time, HCOOH concentration, addition of formate anions) were optimized. Interferences of inorganic acids in photochemical generation were investigated as well. It was found out that the generator with the inside channel provided slightly higher sensitivity and thus generation efficiency than the generator with the PTFE tube wrapped around. Transmission of...

The extraction of mercury species (methylmercury, ethylmercury, phenylmercury and inorganic mercury(II)) from fish tissue, its determination by reverse phase HPLC, UV-photochemical generation of cold vapour, and detection by atomic absorption spectrometry is described in this work. Various extraction agents and digestion methods were compared in order to find the best alternative. The mixture of 6.25% tetramethylammonium hydroxide and 0.05 mol·l-1 hydrochloride acid was chosen as the best extraction agent. In addition to the high extraction efficiency, the solution involved positively not only UV-photochemical generation, but also separation of observed species. On the contrary, the poor repeatability was achieved with the microwave-assisted digestion due to the proved sorption of mercury species on the Teflon vessels. Therefore, the extraction by high temperature (50-60 řC) in glass bottles was preferred. The results of the determination of the mercury species after the extraction from the real samples were compared to the outcomes obtained by AMA 254. The proposed extraction technique together with the RP-HPLC-UV-CVG-QTAAS is suitable for the speciation analysis of mercury.

This thesis deals with the development of a method suitable for determination Te(IV) by UV-photochemical generation of volatile compounds (UV-PVG) in liquid samples. Atomic absorption spectrometry (AAS) and atomic fluorescent spectrometry (AFS) were used as detection methods. The basis of the apparatus for UV-PVG was a mercury lamp wrapped by PTFE capillary. Firstly, the experimental parameters were optimized for both methods. The optimized parameters were the type, concentration, pH and flow rate of the reaction medium, the length of the PTFE reaction coil, carrier gas flow rate (argon), supportive gas flow rate (hydrogen) and atomization temperature. The figures of merit with both detection methods were determined and compared after the method was optimized. Detection limits achieved for these two detection methods were 6,0 µg dm-3 for AFS and 1,50 µg dm-3 for AAS. Performed interference study confirmed a significant effect of many cations of transition metals and hydride forming elements on tellurium determination. The influence of nitric acid in the sample was studied separately. The suitability of the method for tellurium determination was confirmed by using a spiked certified reference material.

The master thesis deals with comparison of atomic fluorescence spektrometry and high resolution continuum source atomic absorption spektrometry for three methods generation of volatile compounds Antimony. In both methods of atomic antimony detection, it compares the most common chemical generation of volatile compounds (hydrides) with two alternative methods - electrochemical and UV - photochemical. The values of performance parameters for the determination of Sb(III) and Sb(V) were determined for all the above combinations. In the case of chemical generation, a surprisingly almost four times higher limit of detection of Sb(III) was found in connection with AFS detection than AAS detection. The final part was devoted to UV - photochemical vapor generation, with AAS detection for Sb(III) reaching limit of detection 4,96 ppb, for Sb(V) 8,63 ppb. Although UV - photochemical generation of volatile antimony compounds did not reach such performance parameters as chemical or electrochemical generation, it was observed that the sensitivity of antimony determination increased greatly when introducing oxygen into the apparatus. The interference study also found a significant positive effect of Fe(II) on the generation efficiency, and this modification partially persisted without further introduction of these...

The mercury occurs in the environment in a variety of forms. Mercury compounds can be found in the soil, atmosphere, water and living organisms. Although some of the mercury substances are very toxic, they are often used in various sectors of industry, agriculture and medicine. Mercury compounds differ in their toxicity, so it is necessary to do speciation analysis. The aim of this diploma thesis was to develop and validate a new analytical method for the determination of mercury compounds in different samples. This method involves the combination of high performance liquid chromatography, UV-photochemical cold vapor mercury generation and atomic absorption spectrometry. Effective separation of mercury(II), methylmercury(I), ethylmercury(I) and phenylmercury(I) ions and subsequent comparable efficient of mercury cold vapor generation from all of forms was achieved using these techniques. The reached detection limits were 8 µg l-1 , 31 µg l-1 , 16 µg l-1 and 38 µg l-1 . At the end of experimental work, the proposed method of RP-HPLC-UV-CVG- QTAAS was used for the determination of mercury compounds in real samples (fish tissue and water samples: Labe, Vltava and tap water) and in certified reference materials (DORM-3 and DOLT-4). Several methods for extraction of mercury species from solid samples...

The presented thesis deals with UV-photochemical generation of volatile compounds of Se and Te from various species. The aim of the project was to expand the current state of knowledge by the application of photocatalytic reduction of higher oxidation states of Se and Te for the speciation analysis based on UV-photochemical generation of volatile compounds. The first step of the study was the assembly of the apparatus for the photocatalysed UV-photochemical generation of volatile compounds. The material of reactor and the whole experimental set-up were based on literature survey and previous research done in our research group. Experiments were directed towards finding the optimum conditions for generation of volatile compounds of selected model elements Se and Te. Se was studied as the element most commonly determined by the UV-photochemical generation of volatile compounds. Conversely, Te was selected as a model analyte representing elements forming less stable volatile compounds. The second part was the application of the optimised method of photocatalysed UV- photochemical generation of volatile Se compound to the determination of Se in water matrices, liquid certified reference materials and also samples of dietary supplements. TiO2/UV-photochemical generation was also successfully modified to...

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...

This thesis deals with the study of UV-photochemical generation of volatile compounds (UV-PVG) in connection with atomic absorption spectrometry (AAS). Selenium (Se(IV)) was selected as a model analyte and many experiments were carried out to expand the current sum of knowledge of the topic. The study was commenced by assembling the UV-PVG apparatus in the continuous flow mode. The detection method used was AAS with externally heated quartz furnace atomizer. The focus of the first step of the study was on the construction of the volatile compounds generator (UV-photoreactor) with emphasis on the material used; tubes made of teflon or quartz of different diameters were tested. The construction of the apparatus was followed by optimization of the reaction conditions (the type and concentration of the photochemical agent and other agents, which increase the analytical signal; the carrier gas and the auxiliary hydrogen gas flow rate; the sample flow rate). Eventually, the analytical figures of merit of the selenium determination using the proposed method were found. The results showed that teflon reaction tubes are a good competitor to those made of quartz. The accuracy of the method has been successfully verified by analysis of certified reference material and its applicability has been further tested...