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Modification of boron doped diamond electrode by electrochemical oxidation of p-aminobenzoic acid
Švárová, Eliška ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
This bachelor's thesis deals with the modification of a boron-doped diamond electrode (BDDE) by the electrochemical oxidation of p-aminobenzoic acid. Subsequently, the stability of the modified electrode was investigated by a study of various parameters. The modification of the electrode was performed using cyclic voltammetry (CV) in LiClO4 electrolyte. The success of the modification and its subsequent stability was investigated by the CV method in electrolyte KCl in the presence of the redox system [Fe(CN)6]4-/3- . Stability was tested in terms of ultrasonic cleaning in isopropanol and anodic cleaning in 0.5 mol l-1 H2SO4. It was found that the modification of the surface cannot be completely removed by ultrasonic cleaning in isopropanol, in contrast, pulses of period 2 seconds with a high positive potential are enough to completely remove the modification. Optimal conditions for surface stability were determined. The ideal number of cycles for surface modification was set at 5 cycles. The use of different electrolytes during modification (KClO4 and LiClO4) determined that in the case of modification in the KClO4 electrolyte, it is possible to measure in the range of the potential window from -400 to +1600 mV and in the case of LiClO4 in the range of -400 to +1500 mV without breaking the modified...
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Electrochemical study of the DNA desorption from the surface of carbon electrodes
Průcha, Jakub ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
This bachelor's thesis deals with the possibility of DNA desorption from the surface of carbon electrodes. Measurements were performed using linear scan voltammetry in a three- electrode configuration, with single-stranded DNA (ssDNA) of 31 nucleotides as the sample. The working electrodes were a boron-doped diamond electrode and an electrode made of highly oriented pyrolytic graphite. The efficiency of desorption was assessed by comparing the heights of oxidation signals of adsorbed nucleic bases, which were measured before and after the application of the desorption procedure. The first approach involved desorption through mixing or rinsing in solutions with different properties, specifically in organic solvents: methanol, acetone, toluene, and DMSO; in acids and bases: HCl, HNO3, NaOH; and subsequently in surfactants and detergents: Triton X-100, TWEEN 80, CTAB, and Tergazyme. Among the tested substances, a 0.1 mol·l-1 solution of NaOH and a 1 % solution of Tergazyme proved to be effective. Subsequently, the time and temperature dependence of the rinsing strength of these two solutions on ssDNA desorption were examined. From the conducted experiments, it was determined that time and temperature of the solution do not increase the efficiency of the desorption by NaOH solution. For rinsing with a...
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Testing of the electrochemical properties of flow-through diamond detector
Pecák, Jakub ; Dejmková, Hana (advisor) ; Vyskočil, Vlastimil (referee)
In the presented bachelor thesis, the functionality of a flow-through multitubular boron- doped diamond electrode (mtBDDE) was verified on two selected neurotransmitters, DA and NE, using the HPLC technique with isocratic elution. An aqueous solution of Britton-Robinson (B-R) buffer was chosen as the mobile phase and a Kinetex EVO C18 reverse column (150 x 4.6 mm) as the stationary phase. The flow rate of the mobile phase was set at 1 ml/min. For electrochemical detection, mtBDDE was used and UV detection at 280 nm was applied as an assistant to the main detector. The electrochemical response of the DA and NE solution (cΘ = 1.10-4 mol/dm3 ) was investigated in the form of hydrodynamic voltammograms over a potential range from 0.1 V to 1.3 V in different pH ranges of the mobile phase (2.5; 4.0; 6.0; 8.0 and 10.0). It was found that the potential wave shifts to lower potentials with increasing pH of the mobile phase, while the response of individual analytes does not change significantly with pH. Under optimal conditions, i.e., mobile phase B-R buffer at pH = 6 and a potential loaded on the mtBDDE of 0.6 V, the repeatability and reproducibility of the measurement results were verified. The electrode gave repeatable results (RSD < 4 %) comparable to the UV detector used (RSD ≤ 4 %) over the series of...
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A new approach to the electroanalysis of primary bile acids and related steroids
Klouda, Jan ; Schwarzová, Karolina (advisor) ; Skopalová, Jana (referee) ; Vyskočil, Vlastimil (referee)
In this doctoral thesis, a novel method for the determination of primary bile acids cholic acid and chenodeoxycholic acid is presented. Bile acids play various vital roles in the mammalian body. Moreover, their determination is extremely helpful in liver and biliary disease diagnosis and management. These saturated organic compounds lack strong chromophores and fluorophores in their structure, and thus are usually hard to detect in spectroscopy. For this reason, either instrumentally advanced but expensive methods, such as mass spectrometry, or less reliable enzymatic methods are commonly employed in bile acids quantitation. Hence, the demand for simple and reliable methods for their determination is strong. Bile acids are also known to be virtually inert for direct electrochemical oxidation. Herein, a simple method for their chemical activation for electrochemical oxidation on bare electrode materials was developed, optimized and applied to cholic acid and chenodeoxycholic acid determination. The activation is based on a dehydration reaction of a primary bile acid with 0.1 mol L-1 HClO4 in acetonitrile (water content 0.55%) that introduces double bond(s) into the originally fully saturated steroid core. This naturally increases the electron density in the structure, and thus allows electrochemical...
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Development of voltammetric methods for detection of phytosterols on carbon-based electrodes
Zelenský, Michal ; Schwarzová, Karolina (advisor) ; Fischer, Jan (referee)
The aim of this diploma thesis was to develop an electrochemical method for three phytosterols, namely stigmasterol β-sitosterol and ergosterol using voltammetry techniques on glassy carbon electrode and boron doped diamond electrode. The work builds on previous results, where it was shown that the electrochemical oxidation of phytosterols requires perchloric acid in acetonitrile. When this acid is used, a dehydration reaction occurs. Calibration dependences were measured here for all phytosterols in an environment with a water content of 0.43%. The stability of the signal with increasing distilled water content was further investigated. Then the calibration dependences in the increased water content were measured again. If we want to use HPLC-type separation techniques, we must first find out how the phytosterols will behave in this environment, and therefore the signal stability on the buffer content was investigated. The buffers used were phosphate and acetate buffer. Subsequently, the concentration dependence was measured in an environment with a higher content of phosphate buffer. Furthermore, the possibility of detecting two phytosterols at once was investigated. Key words: dehydration, glassy carbon electrode, boron doped diamond electrode, oxidation, phytosterols, voltammetry
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Development of electroanalytical methods for detection of bile acids possessing 7α hydroxyl group
Jelšíková, Kristýna ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
This master's thesis contains a study of electrochemical processes of selected bile acids possessing 7 hydroxyl group (cholic, chenodeoxycholic and −muricholic). The measurements were performed on boron−doped diamond electrode in the non-aqueous medium of acetonitrile and perchloric acid (water content 0.55 %) by cyclic voltammetry. It is known that the electrochemical activity of 7 bile acids is increased by a dehydration reaction between perchloric acid and the 7 bile acid. The subject of the study was the stability of the voltammetric response of chemically activated bile acids in the region of negative potentials. It was found that the presence of oxygen in the measured solution is an important factor for obtaining the cathodic signal of 7 bile acids. It probably performs a regenerative function; the product of the electrochemical reduction is re-oxidized in its presence, which leads to an increase in the voltammetric response. At the same time, it is important that the direction of the scan in cyclic voltammetry first proceeds to positive values. A potential of +2.0 V (vs. Ag/AgNO3 in acetonitrile) must be reached for the HO● radicals to be formed. It is these radicals that presumably lead to the formation of the product(s) of bile acids electrochemical oxidation that can be subsequently...
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Optimization of anodic and cathodic pre-treatments of boron doped diamond electrode surfaces for electroanalysis
Baudisová, Kateřina ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
This bachelor thesis deals with the optimization of anodic and cathodic pretreatment of BDD electrodes and subsequent comprehensive characterization and comparison of electrochemical parameters of unmodified, O-terminated and H-terminated BDD electrodes. The study was carried out using cyclic voltammetry of two model inner sphere redox systems [Fe(CN)6]4−/3− and dopamine/dopamine-o-quinone. Boron concentrations in the BDD films ranged from 500 ppm to 8000 ppm. O-termination of the electrode surface was most effectively achieved when an activation potential of Eakt = +3.0 V was inserted for 10 min into 0.5 mol l−1 H2SO4. For the dopamine/dopamine-o-quinone system, the O-terminated BDD electrodes caused deceleration of electron transfer compared to the unmodified BDD electrodes, which was accompanied by an increase in the potential difference with the highest ΔEp at 500 ppm BBD electrode (ΔEp = 711 mV). To achieve the H-terminal surface, single and cumulative reduction was tested by inserting Eakt = −3.0 V. A sufficient single reduction time for the [Fe(CN)6]4−/3− system was determined to be 60 s, whereas in the case of dopamine, the electrochemical parameters did not stabilize at the selected reduction times, but the cathodic and anodic peak signal at the H-terminated 1000 ppm BDD electrode was up...
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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...
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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...
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Study of degradation behavior of abacavir using a diamond film electrode
Pražáková, Lucie ; Kubíčková, Anna (advisor) ; Kozlík, Petr (referee)
In this work the electrochemical degradation behavior of the drug abacavir is studied with the use of boron-doped diamond electrode. Oxidative degradation of the active substance abacavir, used to treat patients with HIV disease, was studied in a batch of three-electrode and two-electrode settings. In this work, the characteristics of five working boron-doped diamond electrodes, differing in a boron/carbon doping ratio of 500 ppm, 1000 ppm, 2000 ppm, 4000 ppm and 8000 ppm, were studied. The degradation in the three-electrode arrangement took place under potenciostatic electrolysis at potentials from 0,6 V to 2,0 V. The degradation in the two-electrode arrangement took place under conditions of potenciostatic electrolysis at higher potentials from 2,0 to 4,5 V. Optimal degradation, to the required values up to 25 %, was achieved at a potential of 3,5 V for an oxidation time of 10 minutes on a boron-doped diamond electrode with a boron/carbon doping ratio of 500 ppm and 1000 ppm. Separation and determination of abacavir and its degradation products were performed by ultra-high performance liquid chromatography with a mass detector. The degradation of abacavir produced two known degradation products, DP1 with relative retention times of 0,40 and DP2 with relative retention times of 0,45. The...
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