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Modification of carbon felt detector with copper microparticles
Baroch, Martin ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
The first aim of this work was to develop copper modified carbon felt electrode for detection of amino acids, which are not electrochemically active on ordinary carbon electrodes. Phenylalanine solution at a concentration 1.0 mmol dm-3 was chosen as the testing solution. Electrode modified with electrochemical deposition of copper from mixture of copper(II) sulphate and sodium sulphate provided very low responses which were decreasing during first measurements, apparently because of insufficient amount of copper. Therefore, further experiments were performed using copper microparticles as a modifier. Copper microparticles activated in nitric acid at a concentration 80 mmol dm-3 were applied at carbon felt by several techniques and in different parts of the felt, i.e. by stirring the felt in microparticles suspension, by dripping of the suspension to the part of the felt in contact with capillary (proximal), between two parts of the carbon felt (sandwich) and at a part of the carbon felt in contact with electrolyte in a measuring cell (distal). Electrodes modified in the distal and in the sandwich arrangement were chosen as the best ones. In the last part, calibration dependences for phenylalanine in concentration range from 0.025 mmol dm-3 to 1.0 mmol dm-3 were measured on the last two electrodes....
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Voltammetric Determination of Sudan I on Silver Solid Amalgam Electrode
Kadeřábková, Marta ; Fischer, Jan (advisor) ; Schwarzová, Karolina (referee)
The subject of this thesis was the development of method for determination of azo dye Sudan I (1-phenylazo-2-naphtol, CAS# 842-07-9) which is used in industry but it is undesirable in food products. The technique of differential pulse voltammetry (DPV) was used on a silver solid amalgam electrode modified by mercury meniscus (m-AgSAE) in 50 % methanol and Britton-Robinson (BR) buffer pH from 2 to 12 supporting electrolyte. Optimal conditions for Sudan I determination were in 50 % methanol and BR buffer pH 4,0, in which it was possible, without the need to regenerate the working electrode surface, to perform repeated measurements. Linear calibration of the substance was obtained in the range 1∙10-6 -1∙10-5 mol∙l-1 and 1∙10-5 -1∙10-4 mol∙l-1 . Limit of quantification was 6,2∙10-7 mol∙l-1 . Subsequently, usability of developed method was tested on samples containing Sudan I and food colorant Sunset Yellow (in the range from 1∙10-6 to 1∙10-5 mol∙l-1 ), but the method for these two analytes was not selective enough.
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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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