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Study of electrochemical behaviour of tauroursodeoxycholic acid at mercury-based electrodes
Pišnová, Kateřina ; Schwarzová, Karolina (advisor) ; Navrátil, Tomáš (referee)
This thesis deals with electrochemical behaviour of tauroursodeoxycholic acid (TUDCA) at silver solid amalgam electrode modified by mercury meniscus (m-AgSAE), polished silver solid amalgam electrode (p-AgSAE) and hanging mercury dropping electrode (HMDE). This thesis is a part of a bigger scientific research that deals with synthesis and characterization of supramolecular systems based on natural steroid compounds and its conjugates. TUDCA offers one reduction peak at m-AgSAE in the environment of Britton - Robinson buffer in range of pH 6.0 - 13.0. The potential of this peak is around −1200 mV. Using cyclic voltammetry was determined that the process on the electrode surface is quasireversible, the reduction is controlled by diffusion and the anodic process is controlled by adsorption. Concentration dependence measured at HMDE by direct current voltammetry in 0.04 mol∙l-1 borat buffer (pH 9.1) is linear in two concentration intervals - 1∙10-3 - 2∙10-4 mol∙l-1 and 1∙10-4 - 8∙10-6 mol∙l-1 of TUDCA. There was no linear dependence between the increase of concentration of TUDCA and the height of the peak obtained on amalgam electrodes by methods DC, DP, cyclic and "square-wave" voltammetry. On HMDE was in several short concentration intervals measured by a CV method a linear dependence of cathodic and...
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Determination of metronidazole on modified carbon paste electrode
Axmannová, Hana ; Dejmková, Hana (advisor) ; Navrátil, Tomáš (referee)
This bachelor thesis examines the possibilities of suppression of the oxygen signal of carbon paste electrode by modification of the electrode with a reductant. Two modifiers were chosen: sodium sulphite and sodium hypophosphite. The unmodified carbon paste electrode was used for the comparison. The possibilities of using these developed electrodes were verified via determination of metronidazole by the differential pulse voltammetry. The conditions for the determination of metronidazole were optimized; for unmodified carbon paste electrode (CPE) buffer of pH 10 was selected as the optimum medium, for carbon paste electrode modified with sodium sulphite (S-CPE) buffer of pH 7 was selected, and finally for carbon paste electrode modified with sodium hypophosphite (F-CPE) buffer of pH 4 was selected as the optimum medium. In this media, concentration dependences were measured and detection and quantification limits were obtained. The possibility of increase of the sensitivity of determination by the accumulation step was studied, but the accumulation of metronidazole was not observed after 5 minutes. The detection and quantification limits for CPE were 1,7×10-5 mol/l and 5,6×10-5 mol/l, for S-CPE 6,8×10-5 mol/l and 2,3×10-4 mol/l and finally for F-CPE 1,3×10-5 mol/l and 4,3×10-5 mol/l. The developed...
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The electrochemical study of the degradation of the natural dyes from historical objects
Ramešová, Šárka ; Schwarzová, Karolina (advisor) ; Navrátil, Tomáš (referee)
The oxidation of quercetin (3,3',4',5,7-pentahydroxyflavone) and luteolin (3',4',5,7-tetrahydroxyflavone) has been studied. These intensively coloured polyphenolic compounds belong to a large group of naturally occuring flavonoid compounds. They were used with advantage as colourants in old tapestries. The study concerns the analysis of degradation processes of the original dyes. Degradation products formed during the ageing process can be used as fingerprints for the determination of the original colours. The degradation processes of flavonoid compounds were studied by electrochemical methods, absorption spectrometry and separation methods in aqueous media. The oxidation mechanism involves electron transfer coupled with chemical reaction and is influenced by the acidobasic properties of quercetin. The dissociation constants pK1 and pK2 of quercetin and pK1 and pK2 of luteolin were determined by combining of independent methods: acid-base titration and UV-Vis spectroscopy. The stability of both compounds significantly depends on the presence of the oxygen. The distribution of the oxidation products of quercetin in aqueous media within the exposure to oxygen was monitored by LC-MS/MS and LC- DAD analysis.
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Mercury speciation determined by thermo-desorption analysis at two sites contaminated by mining
Hojdová, Maria ; Navrátil, Tomáš (advisor) ; Borůvka, Luboš (referee) ; Hruška, Jakub (referee)
Historic mercury mining represents an envinrnmental threat due to high llg concentration in waste materia|. Mercur1'ores \\'ere mined for more than l50 years at t\ťo siles in the centr.a| ('zech Republic, hut thc extent of Hg contamination in the vicinity of former l-lg mining sites has not been yet inr'stigatď. The objectives of the study weÍe to eva|uate thc Hg sorrrces in mine wastes. assess the extent of Hg contamination in historical ntining area ancl to cstimate potential mohility of Hg in the mine waste and soils. The method of thermal tlesorption in combination tvith Í(.P-oES (TDA-lCP.oEs) has been app|ie<l to dctermine llg speciation irr solid samples. Mine rvaste matďa| was samp|e<| at two mining sites. .|edová Hora and Svatá, in ccntral Bohemia. Three soi| profi|es were col|cclď to caphlre likely high and low impact sites rvithin the mining area at Jedová l{ora' Database of thcmto-<|esorption cun,cs o[ I{g chemica| conrpottnds ant| rcference materia|s was crcated for the TDÁ ftrr comparativc purposes. Both mine wastes and soils collected near the llg nines were highly elcvated in total l-lg corcentrations (up to 120 pg g-r and l0 pg g-', respectively). Soils exhibited the highest tlg concentrations mostly in subsurface Ah soil horizons. Higher lJg concentrations in Ah horizons relative...
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Electrochemical studies of the analytical utilization of self-assembled monolayers of calix[4]arene on the surface of polycrystalline gold electrode
Hrdlička, Vojtěch ; Navrátil, Tomáš (advisor) ; Ludvík, Jiří (referee)
This MSc. Thesis deals with electrochemical studies of the analytical utilization of self-assembled monolayers of thiolated calix[4]arene (C4A) and/or undecanthiole (C11SH) on the surface of a polycrystalline gold electrode. Hydroquinone, nitrobenzene, 2-nitrophenole and 4-nitrophenole have been used as tested model compounds. The real surface area of the electrode was determined using these two methods: From the charge of desorption peak of α-gold oxides (5.72±0.48 mm2 ) and using the Randles- Ševčík equation. (6.14±0.59 mm2 ). The preparation of the electrode consisted of polishing on alumina, immersing into piranha solution and cyclic voltammetry. The area of electrode surface was well reproducible. Stability of thiol monolayer in the area of negative potentials was tested. The C11SH layer is very stable; the desorption peak was recorded in basic solutions only (at −1.3 V vs. 3M Ag/AgCl). The position of the desorption peak of C4A is more pH dependent and it was recorded at −1.08 V at pH 13. The properties of the electrode modified by C11SH and or C4A were investigated using the model compound hydroquinone. It is assumed that the oxidation of the hydroquinone does not take place inside the C4A cavity; hence the hydroquinone molecule is too big to pass through the cavity. C11SH and C4 + C11SH act...
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Leaching characterization of platinum group elements from automotive catalytic converters
Štědrý, Robin ; Mihaljevič, Martin (advisor) ; Navrátil, Tomáš (referee)
The distribution of platinum group elements and increase of thein emissions in the environment are mostly related to the use of automobile catalyst. The antropogenic emissions of these noble metals accumulate aloung the roads. The methods such as ICP-OES and XRD were used for determinativ of phase and elemental composition of these samples. The matrix of the gasoline catalyst is composed of Al, Ce oxides with Pt-Pd-Rh coatings. Matrix of diesel catalyst is composed of cordierite with Pt coatings. ICP-MS was used for determination Pt, Pd and Rh. Before the analysis was performed such as pre-concetration fire assay fusion into a NiS button. The leaching characterization of Pt, Pd and Rh was examined during kinetic batch experiments in sodium chloride (1g/l, NaCl), 20 mM Na2P4O7 (NaPyr), fulvic acid (FK, DOC 50 mg/L) and 20 mM citric acid . The results show, that the dissolution of Pt and Pd is the fastest in citric acid and sodium pyrophosphate. Sodium chloride in the concentrations employed, which could be derived from melt waters formed during winter road treatment, does not have a substantiv impal on the speciation and mobilization of Pt and Pd. Organic acid does not have significantly impct on the release of Pt and Pd to the solution. The calculated normalized bulk released NRi values in the range 0,16...
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