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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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The Use of Silver Rotating Disk Electrode to Suppress Passivation During Voltammetric Determination of 4-Nitrophenol
Pitřinec, Jakub ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
In this bachelor's thesis results of the optimization of the measurement of 4-nitrophenol (1·10-4 mol·l-1 ) in the Britton-Robinson (BR) buffer medium on the silver rotating disk electrode are presented with the aim of suppressing the passivation of the electrode surface. The parameters of the differential pulse voltammetry (DPV) technique were optimized for the analytical use of the rotating disk electrode. In BR buffer pH 4,0 and at the electrode rotation speed of 250 rpm calibration dependences of 4-nitrophenol was obtained in the range of (1-10) ·10-5 mol·l-1 under selected optimal conditions and different methods of electrode surface pretreatment. The limit of quantification (LOQ) achieved with polishing before each measurement was 1,7·10-6 mol·l-1 and with polishing only before the concentration change was 8,8·10-6 mol·l-1 .
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Voltammetric Determination of 8-Hydroxy-5-nitroquinoline on a Silver Solid Amalgam Electrode
Bartůňková, Erika ; Vyskočil, Vlastimil (advisor) ; Fischer, Jan (referee)
This Bachelor Thesis is dedicated to the study of the electrochemically active substance 8-hydroxy-5-nitroquinoline. The stability of the prepared standard solution was monitored by UV/VIS spectrometry throughout the electrochemical measurements. A polished silver solid amalgam electrode was chosen as the working electrode. First, the optimum conditions for the measurements were determined by DC voltammetry and differential pulse voltammetry. The calibration dependence was subsequentlymeasuredbybothtechniquesintheconcentrationrangefrom1·10−7 to 1·10−5 mol/L. The DC voltammetry method was also used to measure the calibration dependence in model matrices of drinking and well water in the concetration order of 10−6 mol/L. To further investigate the electrochemical processes and controlling processes in the electrochemical transformation of 8-hydroxy-5-nitroquinoline, the cyclic voltammetry technique was used and applied at different polarization rates.
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Use of a Solid Bismuth Drop Electrode in the Determination of the Drug Metronidazole
Jarošová, Johanka ; Vyskočil, Vlastimil (advisor) ; Fischer, Jan (referee)
The subject of the present Bachelor Thesis was the study of a new commercial solid bismuth drop electrode (SBiDE) and its use to find optimal conditions for the voltammetric determination of the drug metronidazole using the differential pulse voltammetry technique (DPV). The voltammetric behavior of the selected drug was studied as a function of pH of aqueous Britton-Robinson buffer (BR buffer) solution. BR buffer at pH 12 was chosen as the optimal medium for the determination of the drug metronidazole on SBiDE, in which the concentration dependence of metronidazole was measured in the range of 1×10−6 - 6×10−4 mol/L. The limit of quantification (LQ) was 1.38×10−6 mol/L and the limit of detection (LD) was 4.41×10−7 mol/L. The newly developed voltammetric method was used for the determination of metronidazole in the pharmaceutical forms Efloran infusion solution 500 mg/100 mL, Entizol 250 mg tablet, Entizol 500 mg vaginal tablet and Noridem infusion solution 500 mg/100 mL. The selected voltammetric method was compared with the analytical method by UV-VIS absorption spectrometry in the environment of aqueous BR buffer solution at pH 12 in the concentration range of metronidazole 2×10−5 - 8×10−5 mol/L.
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Sulfate determination using ion selective electrode
Hrbková, Petra ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
In this bachelor thesis, literature survey was performed covering the topic of sulphate ion selective electrodes. For sulphates with their very hydrophilic nature and thus position at the end of the Hofmeister series, many ionophores have been tested to ensure sufficient selectivity for ISE. Standard methods used for sulphate determination such as gravimetry, ion chromatography or turbidimetry have certain disadvantages which are overcome by ISE. The basic properties of newly developed sulfate ion selective electrodes were tested. It was found that a sufficient stabilization time of the electrode in a sulfate anion solution of 10−4 mol dm−3 was one day. The electrode with a potential response most closely approximating the theoretical Nernst response showed linear behavior toward the sulfate anion in the concentration range of 10−6 -10−1 mol dm-3 with a slope of −9.2±2.9 mV per order of magnitude; however, the repeatability of the measurement was quite poor. Interference from nitrate, chloride and acetate anions was significant, monohydrogen phosphate and sulfite anions could be considered negligible.
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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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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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Amperometric determination of selected neurotransmitters using porous boron-doped diamond electrode
Vikartovský, Andrej ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
In this work, electrochemical behaviour of porous BDD electrode was observed during the determination of dopamine (DA) and norepinephrine (NE) using flow methods. For the separation of analytes isocratic elution with Britton-Robinson buffer of pH 6,0 was used as mobile phase, with flow rate 1 ml∙min−1. Separation column Kinetex® EVO C18 (150 × 4,6 mm). was used as reversed stationary phase. Porous BDD electrode was used for detection with applied electrical potential 1,1 V and UV detection with wavelenght 280 nm. Dependence of the signal on the concentration of analytes was observed for both detectors in the concentration range from 1∙10−6 to 4∙10−4 mol∙dm−3. Limits of detection, limits of quantification and linear dynamic ranges were determined. To determine stability of porous BDD electrode, repeatability with concentration of analytes 1∙10−4 mol∙dm−3 was measured as well as reproducibility after 4 and 6 weeks with same condition of measurement.
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Voltammetric Determination of 2,4-Dichlorophenoxyacetic Acid and 2,4-Dichlorophenol on a Screen-Printed Carbon Electrode
Jančová, Jana ; Vyskočil, Vlastimil (advisor) ; Fischer, Jan (referee)
The aim of the presented Master Thesis was to study an electrochemical behaviour of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4-dichlorophenol (2,4-DCP) resulting in the founding of optimum conditions for their voltammetric determination at a screen-printed carbon electrode (SPCE) using DC voltammetry (DCV) and differential pulse voltammetry (DPV). Voltammetric behaviour of both compounds was investigated in dependence on the pH of the medium (realized using Britton-Robinson buffer). The optimum pH for the voltammetric determination of 2,4-D on the SPCE was chosen to be pH 5,0 for both voltammetric techniques, and, for 2,4-DCP, it was chosen to be pH 6,0 for both voltammetric techniques. The determination of 2,4-D at a concentration of 1·10-4 μmol·L-1 showed good repeatability for both voltammetric techniques used (1.3% for DCV and 0.7% for DPV), and, for 2,4-DCP, it showed acceptable repeatability for both voltammetric techniques used (1.3% for DCV and 4.8% DPV). Under optimum conditions, the calibration dependence of 2,4-D was measured for DCV in the concentration range of 10-100 μmol·L-1 , with limit of quantification (LOQ) of 1.0 μmol·L-1 and limit of detection (LOD) 0.3 μmol·L-1 . Under optimum conditions, the calibration dependence of 2,4-D was measured for DPV in the concentration range...
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