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Influence of surface termination of boron-doped diamond electrode on the electrochemical behaviour of phenol and its derivatives
Nedvěd, Michal ; Schwarzová, Karolina (advisor) ; Gabriel, Jiří (referee)
This thesis is devoted to the study of electrochemical oxidation of meta-substituted phenolic substances on a boron-doped diamond electrode. In the first phase, it was studied the effect of pH on their electrochemical oxidation by the methods of classical "direct current" voltammetry (DCV) and differential pulse voltammetry (DPV). The study was performed on three types of boron doped diamond (BDD) surfaces: polished, anodic and cathodically activated. In the second phase, attention was paid to the Hammett correlation to study the effect of the substituent on the potential of electrochemical oxidation of selected phenolic compounds. Among the substituents studied were (-H, -CH3, -OCH3, -(CH2)2COOH, -COOH a -NO2). In general, the oxidation potentials were lower in the basic medium than in the acidic medium on all studied surfaces. An exception was the studied phenolic acids, which could not be detected in an alkaline medium on the O-terminated BDD, probably due to electrostatic repulsion between the partially negative electrode surface and the acid dianion. The highest correlation coefficient for the dependence composed of all studied phenols was obtained for the polished and H-terminated surface at pH 11, ie the dissociated form of phenolic substances. The high electron density leads to easy...
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Design of an electrochemical sensor for ethanol measurement
Božek, Jakub ; Jankovský, Jaroslav (referee) ; Otáhal, Alexandr (advisor)
This bachelor thesis deals with printed electrochemical sensors and the measurement of glucose and ethanol in blood solution. The theoretical part describes the sensors, their distribution and applications. Then the thesis focuses in detail on electrochemical sensors, measurements and their electrodes. Then, in the practical part, the sensor designs, fabrication of the sensors and the measurements made are presented.
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Determination of trace amounts of mercury by voltammetry
Hudzíková, Veronika ; Mravcová, Ludmila (referee) ; Řezáčová, Veronika (advisor)
This bachelor thesis concentrates on the optimalization of conditions for voltammetric determination of mercury in water. The theoretical part describes fundamental characteristics of mercury as a chemical element, impact on the environment and possible analytical methods for determination with emphasis on voltammetry. The experimental part includes the description of the optimalization of analysis conditions, applied methods and the analysis of real samples.
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Optimization of electrodeposition of polyaniline on platinum electrode for propanol oxidation
Dobiášová, Klára ; Schwarzová, Karolina (advisor) ; Coufal, Pavel (referee)
Optimization of electrodeposition of polyaniline on platinum electrode for propanol oxidation Dobiášová Klára 2023 Abstract Composites of polyaniline (PANI) with rare metal nanoparticles (metal/PANI) are a promising material for the oxidation of aliphatic alcohols. In this work, the deposition of a polyaniline (PANI) film on a platinum electrode (Pt-PANI electrode) was performed potentiostatically and using cyclic voltammetry (CV). For both methods, the parameters influencing the deposition were optimized. For cyclic voltammetry, electrodeposition in aniline solution is significantly influenced by the final potential Efin of the scan. The PANI film with the highest current response during the deposition itself, which correlates with the thickness of the formed film, was created in the case of Efin + 1.1 V; i.e. the peak potential of the aniline oxidation peak. However, this method proved unreliable due to the poor reproducibility of the current response corresponding to PANI formation. For the PANI film formed by the CV method, its color change related to its oxidation state was investigated, with the color change being imperceptible to the naked eye in a basic environment and the most visible colour change occurring between + 0.05 V and + 0.2 V in an acidic environment. Potentiostatic deposition of...
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Development of methods for the voltammetric determination of chloramphenicol and dinitramin at amalgam electrodes
Štafurová, Kristína ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
The first part of this diploma thesis deals with the determination of chloramphenicol (CLF) on the retractable-pen-based renewable silver amalgam film electrode (RAE) by differential pulse voltammetry (DPV). Calibration dependencies in the concentration range of 10-100 µmol dm−3 and 1-10 µmol dm−3 were obtained. Repeated RAE surface restoration when determining CLF does not contribute to the repeatability of the signal. The determination limit was 2,2 µmol dm−3 . In the second part of the work, the conditions for the determination of dinitramine (DN) were examined on the meniscus-modified silver solid amalgam electrode by DPV technique. The Britton-Robinson buffer pH 5 was chosen as the optimal medium. In this electrolyte, the impact of regeneration potentials on DN signal stability was monitored. Regeneration pulses or methanol rinses did not contribute to the stability of the signal. There is a strong passivation on the electrode, so this type of electrode is not suitable for determination of this analyte. The possible solution is to use RAE, in which mechanical surface restoration is an effective way of solving the passivation on the electrode surface. In the third part of the work, dinitramine was studied at the RAE. The best repeatability of the measurements was achieved by activation of the...
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Development of voltammetric methods for detection of bile acids and their conjugates
Petráňová, Karolína ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this thesis is to study the electrochemical properties of bile acids and their conjugates. Specifically, cholic acid, chenodeoxycholic acid, taurocholic acid, taurochenodeoxycholic acid, glycocholic acid, and glycochenodeoxycholic acid were studied. The measurements were carried out on a boron-doped diamond electrode in an environment of acetonitrile and perchloric acid, with a water content of 0.55% in the solution by method of cyclic voltammetry. In order for bile acids to be electrochemically active, they must first be dehydrated, which takes place in a reaction with perchloric acid. This reaction requires a relatively long time, so it was accelerated by heating the compounds. The goal of this work was to determine the conditions under which the dehydration products of bile acids can be detected. The water content that can be added to the solution after dehydration to keep the voltammetric signal stable was determined. Furthermore, it was found that the voltammetric determination can be carried out even at a pH that is not extremely acidic in which is the the dehydration carried out. Finally, calibration dependencies were compiled.
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Development of electrochemical methods for study of antibacterial compounds in small volumes
Gajdár, Július ; Barek, Jiří (advisor) ; Šiškanova, Tatiana (referee) ; Labuda, Ján (referee)
Main goal of this Ph.D. thesis is to develop voltammetric methods for the electrochemical study of novel antimycobacterial compounds hydroxynaphthalene- carboxamides. Firstly, this study was focused on the miniaturization of voltammetric methods and construction of an electrochemical microcell due to usually small volume of samples that are associated with an analysis of biologically active compounds in biological matrices. Therefore, all aspects of the voltammetric procedure were studied in a relation to miniaturization. Microcells were based on commercially available electrodes: glassy carbon electrode as a reliable electrode material with well-described characteristics and a novel silver solid amalgam electrode. This study was carried out with analytes 4-nitrophenol, pesticide difenzoquat, and 1-hydroxy-N-(4-nitrophenyl)naphthalene-2-carboxamide. Attention was paid especially to the optimization of oxygen removal procedures in the drop of a solution. Developed miniaturized methods had the same parameters for the determination of studied compounds as in bigger volumes. The proposed electrochemical microcell can be generally used for voltammetric analysis of those samples of biological or environmental origin that are usually available in very limited volumes. Second part of the thesis was focused...
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The width of potential window of boron doped diamond electrodes in dependence on their pretreatment and composition of the mixed electrolyte solution
Dvořáková, Klára ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The diploma thesis focuses on the range of the potential window of the BDD electrode in dependence on the composition of the mixed electrolyte solution and the treatment of the electrode surface. The measurements were performed on a polished (p-BDD) and O-terminated (O-BDD) electrode by the method of linear sweep voltammetry (LSV) in a three-electrode system. It was confirmed that in an environment with a suitable organic solvent, the range of the potential window widens. The measured solutions consisted of deionized water containing sodium perchlorate with a concentration of 1 mmol l−1 and one organic solvent in which sodium perchlorate with a concentration of 1 mmol l−1 was also dissolved. Acetonitrile, methanol, N,N-dimethylformamide and isopropanol were used in solutions (0 %, 1 %, 5 %, 10 %, 50 %, 70 %, 90 %, 95 %, 99 % or 100 % volume percent). Expansion, or the shortening of the potential window range was evaluated separately for each solvent in the anodic and cathodic regions. The expansion of the window on both sides was confirmed in acetonitrile as the concentration of the solvent increases, so it is based on this experiment as a universal solvent suitable for the determination of reducing and oxidizing analytes, from measurements on O-BDD and also on p-BDD. In the case of the remaining...
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Voltammetric Determination of Psilocin and Psilocybin at Carbon-fiber PLA Electrode
Choińska-Mlynarczyk, Marta ; Navrátil, Tomáš
Psilocin and psilocybin are two neuroactive drugs. They can be used in experimental treatment in psychiatry, moreover, also as illicit drugs to achieve hallucinations and relaxation. Easy access to these two alkaloids indicates that their monitoring in the environment and the body fluids is necessary. Electrochemistry offers fast, simple, and easy methods of their determination using laboratory-manufactured electrodes from 3D printed carbon-fiber polylactic materials. This technique of electrode fabrication can be characterized by many benefits, e.g., desired shape or diameter of the electrode, well-developed voltammetric signals, and low background currents.
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Differences in Electrochemical Reduction of Mono- and Polynuclear Acylgermanes
Liška, Alan ; Frühwirt, P. ; Haas, M. ; Ludvík, Jiří ; Gescheidt-Demmer, G.
Ail the studied compounds accept first electron under formation a stable anion radical. The\ncorresponding reduction potentials in aprotic media depend on electronic (inductive,\nmesomeric) properties of the substituents, their number, and position. Here, aromatic acyl group\n(benzoyl group with various substitution on aromatic ring) is the principal substituent. The\nredox properties of presented organoelement compounds with central heteroatom Ge (Si, Sn)\nare controlled by peripheral carbonyl groups (in role of redox centers), their number, and\naromatic ring substitution. The measured first reduction potentials E1 values are found in wide\nrange (> 900 mV) due to the fact that the redox centers are carbony 1 groups connected through\nheteroatom in case of acylgermanes, while for di- and trinuclear derivatives (which are\nmolecules with multiple redox centers) the easiest reducible center is the bridging aromatic unit\ninfluenced by the closest carbonyl groups. Thus, it is possible to distinguish both groups ofnonequivalent\ncarbonyl substituents.
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