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Development and utilization of electrochemical flow-through detectors
Baroch, Martin
The proposed dissertation thesis deals with the development and investigation of electrochemical flow systems using both conventional and unconventional electrode materials. In the first part of this thesis, the problem of porous flow-through large area electrodes is addressed. As a working electrode material, a free-standing porous boron-doped diamond (fs-pBDD) was used. This was used for the first time in the construction of an electrochemical cell designed for amperometric detection in flow methods. Testing of this electrode was performed using amperometric detection combined with flow injection analysis of a ruthenium complex solution. The detection limits achieved on this material were in the submicromolar range and the linear dynamic range of the concentration dependence spanned over three orders of magnitude. In addition to amperometry, fs-pBDD was also subjected to testing by cyclic voltammetry. The main reason for using this method was to determine the electrochemically active area, which contributed to the overall physicochemical characterization of this promising material. However, it was this step that brought into question the accuracy and precision of the calculation used. For this reason, the search for new ways to calculate the electrochemically active area of the working electrode...
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Development and utilization of electrochemical flow-through detectors
Baroch, Martin ; Dejmková, Hana (advisor) ; Vyskočil, Vlastimil (referee) ; Trnková, Libuše (referee)
The proposed dissertation thesis deals with the development and investigation of electrochemical flow systems using both conventional and unconventional electrode materials. In the first part of this thesis, the problem of porous flow-through large area electrodes is addressed. As a working electrode material, a free-standing porous boron-doped diamond (fs-pBDD) was used. This was used for the first time in the construction of an electrochemical cell designed for amperometric detection in flow methods. Testing of this electrode was performed using amperometric detection combined with flow injection analysis of a ruthenium complex solution. The detection limits achieved on this material were in the submicromolar range and the linear dynamic range of the concentration dependence spanned over three orders of magnitude. In addition to amperometry, fs-pBDD was also subjected to testing by cyclic voltammetry. The main reason for using this method was to determine the electrochemically active area, which contributed to the overall physicochemical characterization of this promising material. However, it was this step that brought into question the accuracy and precision of the calculation used. For this reason, the search for new ways to calculate the electrochemically active area of the working electrode...
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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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Determination of synthetic antioxidants using HPLC with electrochemical detection on carbon felt detector
Baroch, Martin ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
Title: Determination of synthetic antioxidants using HPLC with electrochemical detection on carbon felt detector Author: Martin Baroch Supervisor: RNDr. Hana Dejmková, Ph.D. Department: Department of Analytical Chemistry The aim of this work was to find suitable conditions for HPLC separation with subsequent coulometric detection on a carbon felt detector. The analytes were synthetic phenolic antioxidants, specifically propyl gallate (PG), tert-Butylhydroquinone (tBHQ), butylated hydroxyanisole (BHA) and butylhydroxytoluene (BHT). For the complete separation of the analytes, gradient elution was required. As a mobile phase methanol and acetate-phosphate buffer of pH 4.5 were used. Concentration of methanol in mobile phase was linearly increased from 55 % to 95 % during 8 minutes and next 2 minutes was concentration of methanol held at 95 %. As a stationary phase was used Lichrospher® RP- 18 (125×4 mm, 5 µm) (LichroCART) column. Potentials putted on a carbon-fiber working electrode were 1.40 V for BHT and 0.80 V for other analytes. Two potentials were chosen for a better detector response to BHT. The calibration dependence of the signal on the concentration was observed in the concentration range of · 10-4 - 1 · 10-6 mol dm-3 for all analytes. In this range the dependencies are linear. Inaccurate...
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