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National Repository of Grey Literature 2 records found  Search took 0.01 seconds. 
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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