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Development and utilization of electrochemical flow-through detectors
Baroch, Martin ; Dejmková, Hana (advisor) ; Vyskočil, Vlastimil (referee) ; Trnková, Libuše (referee)
The proposed dissertation thesis deals with the development and investigation of electrochemical flow systems using both conventional and unconventional electrode materials. In the first part of this thesis, the problem of porous flow-through large area electrodes is addressed. As a working electrode material, a free-standing porous boron-doped diamond (fs-pBDD) was used. This was used for the first time in the construction of an electrochemical cell designed for amperometric detection in flow methods. Testing of this electrode was performed using amperometric detection combined with flow injection analysis of a ruthenium complex solution. The detection limits achieved on this material were in the submicromolar range and the linear dynamic range of the concentration dependence spanned over three orders of magnitude. In addition to amperometry, fs-pBDD was also subjected to testing by cyclic voltammetry. The main reason for using this method was to determine the electrochemically active area, which contributed to the overall physicochemical characterization of this promising material. However, it was this step that brought into question the accuracy and precision of the calculation used. For this reason, the search for new ways to calculate the electrochemically active area of the working electrode...
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Electrochemical detection of n-propanol on Au and Pt electrodes modified with polyaniline-based composites
Pejzlová, Michaela ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
The electrochemical oxidation of aliphatic alcohols is problematic on conventional electrode materials and to develop methods for their detection, the catalytic properties of electrode surfaces need to be exploited. This thesis is concerned with the study of the electrochemical deposition of polyaniline (PANI) in acidic media on three different electrodes, platinum, gold and glassy carbon electrode. The properties of the PANI modified electrodes were tested in comparison to the unmodified electrodes. The electrooxidation of aliphatic alcohols n-propanol and 2-propanol in alkaline medium was studied by cyclic voltammetry. Subsequently, the effect of electrodeposited noble metals (palladium and gold) on the surfaces of unmodified and PANI modified electrodes on the electrooxidation of propanol was investigated by using the same procedures. From the linear part of the concentration dependence of n-propanol on the chosen electrodes, the limit of detection was determined. The lowest value was calculated for the platinum electrode with electrodeposited gold (LOD = 0.2 mmol l−1 ). PANI modified electrodes showed wider linear dynamic range than electrodes without this modification. Keywords: cyclic voltammetry, electrooxidation, glassy carbon electrode, gold electrode, metal electrodeposition, n-propanol,...
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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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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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Voltammetric Determination of Warfarin at a Screen-Printed Carbon Electrode
Žužičová, Victória ; Vyskočil, Vlastimil (advisor) ; Dejmková, Hana (referee)
In this Bachelor Thesis, the electrochemical behaviour of the drug warfarin sodium was studied at a screen-printed carbon electrode (SPCE) using DC voltammetry (DCV) and differential pulse voltammetry (DPV). The dependence of the voltammetric behaviour of the substance on the pH of the medium was studied in Britton-Robinson buffer (BR buffer) in the pH range of 2.0−12.0. A pH of 7.0 was chosen as the optimum pH for both voltammetric techniques. A repeatability of 3.8% for DCV and 4.3% for DPV was determined for the selected pH. Calibration dependence was monitored under the selected optimal conditions in the concentration range 2∙10−6 to 1∙10−4 mol∙dm−3 . The limit of detection (LOD) was determined to be 1.05∙10−6 mol∙dm−3 for DCV and 2.59∙10−7 mol∙dm−3 for DPV. The limit of quantification (LOQ) was 3.50∙10−6 mol∙dm−3 for DCV and 8.62∙10−7 mol∙dm−3 for DPV. These newly developed methods were used for the determination of the active ingredient in the pharmaceutical formulation Warfarin Orion 5 mg. The values measured by voltammetric methods were compared with those obtained by spectrophotometric measurements. Key words Electrochemistry, Warfarin, Anticoagulants, Direct Current Voltammetry, Differential Pulse Voltammetry, Screen-Printed Carbon Electrode
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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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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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