National Repository of Grey Literature 121 records found  previous11 - 20nextend  jump to record: Search took 0.01 seconds. 
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...
Determination of cholesterol, 7-dehydrocholesterol and cholecalciferol by HPLC with spectrophotometric and electrochemical detection
Dostálková, Lucie ; Schwarzová, Karolina (advisor) ; Vyskočil, Vlastimil (referee)
The aim of this thesis is to verify the possibility of simultaneous determination of three structurally related biologically active substances (cholesterol, 7-dehydrocholesterol and cholecalciferol) after previous separation by high-performance liquid chromatography followed by electrochemical (on a boron-doped diamond electrode) and spectrophotometric detection, which were compared in this work. The influence of the water content in the mobile phase (in the range of 0-10 %) on the retention factor of the analytes and their response for both types of detectors was investigated. Using all mentioted water contents, the analytes baseline-separated. As the water content increased, the retention factor of the analytes increased as well as the background current for higher positive detection potentials. Based on the recorded hydrodynamic voltammograms, the optimum detection potential + 1.8 V was chosen. The optimum wavelength for spectrophotometric detection was 200 nm. The concentration dependence was measured in an of 50 mmol l−1 sodium perchlorate in acetonitrile mixed with water (95:5, v/v). The spectrophotometric detector provided lower detection limits compared with the electrochemical detector, which had detection limits of 2.3 μmol l−1 for cholesterol, 1.4 μmol l−1 for 7-dehydrocholesterol and...
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.
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...
Voltammetric behaviour of cholesterol and lanosterol on boron doped diamond electrode
Kubešová, Jana ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this thesis is to investigate procedures leading to regeneration of boron- doped-diamond's (BDD electrode) surface and study of voltammetric behaviour of cholesterol and lanosterol on BDD electrode. Three options of regeneration of electrode's surface were were studied: the stirring, the mechanical polishing using alumina and the anodic oxidation. The anodic oxidation was studied using electrolytes: 0,1 mol l−1 perchloric acid in acetonitrile, 0,1 mol l−1 sodium perchlorate in acetonitrile and tetrahexylammonium hexafluorofosphate in acetonitrile. Each electrolyte was studied with 0 or 0,43 % and 20 % volume of water. Further, voltammetric behaviour of cholesterol on BDD electrode in the presence of 0,1 mol l−1 perchloric acid in acetonitrile was investigate. The second part of the thesis was the study of voltammetric behaviour of lanosterol on BDD electrode in the presence of 0,1 mol l−1 perchloric acid in acetonitrile and 0,1 mol l−1 sodium perchlorate in acetonitrile. The study was performed using cyclic voltammery. Lanosterol provides two anodic signals in the presence of both electrolytes, the first one at the potential of +1200 mV, the second one at the potential of +1500 mV. The stability of lanosterol in the presence of perchloric acid and sodium perchlorate was studied by...
Comparison of the gold microelectrode and conventional electrode for the saccharide determination using pulsed amperometry
Smítková, Karolína ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
This bachelor's thesis deals with combination of pulsed amperometric detection (PAD) with flow injection analysis (FIA) in order to use them to detect glucose and consequently carbohydrates in solution. Pulsed amperometry is efficient detection method for many of organic compounds in which, as the name suggests, a sequence of three or four potential pulses is applied at the working electrode. If the pulse parameters are suitable, then it is possible to eliminate the unwanted passivation of the working electrode due to the adsorption of oxidation products and intermediate products of aliphatic compounds, which would lead to a reducion of its active surface. The aim od this work is to show the effect of the change of the value of the applied potential pulses on the peak heights corresponding to the oxidation of the glucose in solution and to evaluate their repeatability. As a working electrode, it compares a gold electrode of conventional size and a gold microelectrode. The determination was performed in a borate buffer with pH = 10. First of all, cyclic voltammograms of solution with concentration of glucose 1·10-2 mol dm-3 were measured to obtain the initial values of the applied pulses. Subsequently, the dependence of the peak heights on their injection order for different values of individual...
Electrochemical properties of synthetic drugs 3-fluorophenmetrazine and 4-methylpentedrone
Jiroušková, Eliška ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The aim of this Thesis was to clarify electrochemical properties of two new psychoactive substances. These substances are an alternative to classical drugs because they are not controlled by current legislation. It is important to determine the metabolites of these substances to be able to detect them in organism. Their electrochemical properties could explain the process of the first phase of biotransformation in human organism. Two synthetic stimulants were studied - 3-fluorophenmetrazine and 4-methylpentedrone, used as substitutes for cocaine or ecstasy. The purity of substances was controlled by HPLC with UV/Vis diode array detector and the stability was verified by UV/Vis spectrophotometry. Electrochemical properties were studied in phosphate buffer using cyclic voltammetry. For both substances was calculated theoretical HOMO and LUMO spatial distribution. This information was important to estimate parts of molecules, that can be reduced or oxidised. The analytical method was developed on glassy carbon electrode using differential pulse voltammetry. Substance 3-fluorophenmetrazine was determined in phosphate buffer pH 9,0 with limit of detection of 5,1 µmol l-1 . The linear range of calibration curve is from 7,0 to 107,0 µmol/l, R = 0,9988. 4-methylpentedrone was determined in phosphate...

National Repository of Grey Literature : 121 records found   previous11 - 20nextend  jump to record:
See also: similar author names
3 SCHWARZOVÁ, Kateřina
3 Schwarzová, Kateřina
2 Schwarzová, Klára
10 Schwarzová, Kristýna
Interested in being notified about new results for this query?
Subscribe to the RSS feed.