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Determination of antioxidant activity of lichens
Jirásková, Barbora ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
Antioxidant properties were studied on seven members of the Cladonia lichen family using the DPPH method, Reducing Power method, Folin-Ciocalteu method and two electrochemical methods: cyclic voltammetry (CV) and flow injection analysis (FIA) with amperometric detection.Both electrochemical methods were carried out with the use of glassy carbon electrode (GCE) and carbon paste electrode (CPE), FIA and CV were evaluated on the potential of E = 1,2 V. The carbon paste electrode turned out not to be ideal for these kinds of measurements, possibly for unknown interactions betweeen the carbon paste and the analysed extract. The inapplicability of the electrode took shape of low to zero correlation between this and most of the other methods. Evaluation of the measured data could infer that the studied Cladonia family lichens really contain substances with antioxidant properties, of which the most would probably be of phenolic type.
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New Methods of Oxygen Removal from Analyzed Solutions in Voltammetric Determination of Organic Compounds
Batěk, Jan ; Vyskočil, Vlastimil (advisor) ; Schwarzová, Karolina (referee)
The aim of this Bachelor Thesis was to verify new methods of oxygen removal from analyzed solutions in voltammetric determination of organic compounds. A method of chemical reduction was chosen to remove dissolved oxygen. Carbohydrazide, N,N-diethylhydroxylamine and 2-butanone oxime were used for removal of dissolved oxygen. These substances are used to remove oxygen from boiler systems. The last agent used to remove oxygen was sodium sulfite. Differential pulse voltammetry (DPV) was used to monitored the ability of oxygen scavengers. The effect of pH of the solution (Britton-Robinson buffer) on oxygen removal was also investigated. A solution of 4-nitrophenol at a concentration of 1∙10−4 mol∙l−1 was used as a model substance in these assays. We have found that carbohydrazide had no effect to remove oxygen in the whole pH range. Using sodium sulphite, oxygen was removed from the analyzed solution at pH 8, 10 and 12. Determination of 4-nitrophenol was thus possible. Using N,N-diethylhydroxylamine at pH 10 and 12 and 2-butanone oxime at pH 8, 10 and 12, oxygen was removed from the analyzed solutions. However, these substances are unsuitable for the determination of 4-nitrophenol.
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Development of electroanalytical methods for detection of cholesterol and 7-dehydrocholesterol
Benešová, Lenka ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The aim of this Thesis is development of electroanalytical methods for determination of cholesterol and 7-dehydrocholesterol on boron doped diamond electrodes based on electrochemical oxidation of products of acid-induced dehydration reaction. Two approches have been applied, relying on their detection in 0,1 mol.l-1 perchloric acid in acetonitril containing variable water content 0,43 % - 40 %. Cyclic voltammetry revealed substantial difference in oxidation peak pontecials for 7-dehydrocholesterol (+850 mV) and cholesterol (+1500 mV) in 0,1 mol.l-1 perchloric acid in acetonitrile containing 5 % of water. The limit of detection using differential pulse voltammetry were 6,19 µmol.l-1 a 19,2 µmol.l-1 for a mixture of 7-dehydrocholesterol and cholesterol, respectively. For flow injection analysis with amperometric detection (FIA-AD) the water content in run buffer, detection potencial and the distance between the capillary outlet and electrode surface in wall-jet arrangement of amerometric flow-through detection cell were optimized. Achieved detection limits are in range of 0,61 - 3,43 µmol.l-1 depending on the detection potencial and water concent in the run buffer. The developed FIA-AD method was used for determination of a model mixture solution of 7- dehydrocholesterol and cholesterol. Key words...
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