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Study of redox reactions and adsorption of 4-nitrophenyl triazole labeled nucleosides and cresols on boron doped diamond electrodes for development of electroanalytical methods
Vosáhlová, Jana ; Schwarzová, Karolina (advisor) ; Havran, Luděk (referee) ; Navrátil, Tomáš (referee)
In this work, the application of boron-doped diamond electrodes with various surface pre- treatment were tested on selected oxidizable and reducible model compounds, specifically para and ortho cresols and 2'-deoxycytidine and 7-deazaadenosine labeled by 4-nitrophenyl triazole. The aim of the study was the investigation of electrochemical and adsorptive processes with respect to the development of electroanalytical methods of detection of the selected compounds, or utilization of boron-doped diamond electrodes as detectors in liquid-flow systems. Cresols were used as the model oxidizable compound. On O-terminated and polished boron- doped diamond electrodes, cresols provide oxidation signal owing to their oxidation to methylphenoxy radical at comparable potentials as on other carbon-based electrodes used as a reference in this work, i.e., glassy carbon electrode, pyrolytic graphite electrode, and carbon paste electrode. These carbon electrode materials show relatively high propensity to adsorption of reaction products, while such adsorption is minimal on boron-doped diamond. In situ anodic activation allows for a rapid regeneration of boron-doped diamond surface prior to each scan. A differential pulse voltammetric method that was developed with a detection limit of 0.61 mol∙l-1 to 2.97 mol∙l-1...
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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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Voltammetric Determination of 7-Dehydrocholesterol as a Biomarker of Smith-Lemli-Opitz Syndrom
Zárybnická, Adéla ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this thesis was the development of a voltammetric method for the determination of 7-dehydrocholesterol as a biomarker of congenital disease Smith-Lemli-Opitz syndrome. The concentration of 7-dehydrocholesterol in plasma will increase hundred-fold to hundreds to thousands µmol L-1 in patients suffering from Smith-Lemli-Opitz syndrome. The determination of 7-dehydrocholesterol was carried out in artifical serum in this work, which was prepared to mimic the conditions of postnatal diagnosis of Smith-Lemli-Opitz syndrome. 7-dehydrocholestrol provides a well developed voltammetric signal at approximately +0.8 V vs. Ag/AgNO3 in acetonitrile. Differential pulse voltammetry with optimized parameters was used for the determination of 7-dehydrocholesterol. The presence of protein in artificial serum (human serum albumin) resulted in an unacceptably high detection limit of the method (178 µmol L-1 in artificial serum). Therefore, human serum albumin was eliminated from the artificial serum samples by precipitating it with acetonitrile and subsequently centrifuging the resulting suspension. At the same time, the ratio of aqueous and organic components in the studied medium was also adjusted with acetonitrile to achieve an optimal voltammetric response of 7-dehydrocholestrol. With regard to the...
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Development and application of electrochemical flow-through detector with renewable working material
Mika, Jan ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee) ; Metelka, Radovan (referee)
The aim of this thesis was development and initial testing of new porous electrochemical detector for flow-through arrangements, especially for flow injection analysis (FIA) and liquid chromatography. One of the most advantageous properties of the detector is simple renewal of working material and thus its suitability for determination of strongly passivating substances. Glassy carbon microbeads and copper microparticles were tested as a working material within this study. Initially, basic electrochemical properties of the glassy carbon-based detector were examined by FIA using hydroquinone and potassium ferrocyanide as model substances. For both model substances high degree of conversion was achieved (around 100 %), and thus it was concluded that glassy carbon-based detector can be considered as coulometric. Hereafter, practical application of the carbon-based detector are presented on five electrochemically active substances closely related to the human medicine and pharmacy - thymol, tyrosine, sulfamethizole and vanillylmandelic acid (VMA) simultaneously determinined with homovanillic acid (HVA). Complexity of instrumental arrangement of flow-through methods had been increasing consecutively up to the HPLC determination with gradient programme. It was proved that the carbon-based detector is...
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Boron doped diamond and its utilization in electroanalysis of derivatives of aromatic compounds
Zavázalová, Jaroslava ; Schwarzová, Karolina (advisor) ; Šelešovská, Renáta (referee) ; Navrátil, Tomáš (referee)
This work is devoted to the study of boron doped diamond as electrode material, its properties and use in electroanalytical methods - in voltammetric and subsequently amperometric methods in combination with high performance liquid chromatography. The series of boron doped diamond films was tested with respect to the effect of boron concentration on their morphology, quality, electrochemical and spectral properties using scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and cyclic voltammetry and differential pulse voltammetry. Further, the effect of boron concentration on the determination of selected substances was investigated, both for their oxidation (2-aminobiphenyl, benzophenone-3) and for their reduction (5-nitroquinoline). Furthermore, a voltammetric and amperometric method was developed for the determination of a mixture of aminobiphenyls and aminonaphthalenes using a boron doped diamond electrode. The effects of activation cleaning programs on the signal of benzophenone-3 were investigated using a boron doped diamond electrode, and the determination of benzophenone-3 on boron doped diamond electrode in the presence of the selected surfactant was studied. Boron doped diamond as carbon-based material was compared with other selected carbon materials such as glassy...
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Voltammetric behaviour of cholesterol on glassy carbon electrode
Bláhová, Eva ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this Thesis is a study of voltammetric behaviour of cholesterol on glassy carbon electrode in the presence of acetonitrile and strong acid. The electrochemical oxidation occurs after dehydration of cholesterol induced by the acid. The study was performed using cyclic voltammetry, mostly in the presence of perchloric acid. Further, influence of other acids - sulphuric, nitric and phosphoric acid - was studied. Cholesterol provides in the presence of perchloric and sulphuric acid one anodic signal at the potential of +1400 mV vs. Ag/0,01 mol.l-1 AgNO3 in 1 mol.l-1 NaClO4 in acetonitrile. The influence of polarization rate, water content and concentration of perchloric acid in the supporting electrolyte on the oxidation signal of cholesterol was studied. Calibration dependence of cholesterol was measured using differential pulse voltammetry. The limit of detection was determined to be 4,83.10-6 mol.l-1 . Key words: Dehydration, glassy carbon electrode, cholesterol, oxidation, voltammetry
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Modification of carbon felt detector with copper microparticles
Baroch, Martin ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
The first aim of this work was to develop copper modified carbon felt electrode for detection of amino acids, which are not electrochemically active on ordinary carbon electrodes. Phenylalanine solution at a concentration 1.0 mmol dm-3 was chosen as the testing solution. Electrode modified with electrochemical deposition of copper from mixture of copper(II) sulphate and sodium sulphate provided very low responses which were decreasing during first measurements, apparently because of insufficient amount of copper. Therefore, further experiments were performed using copper microparticles as a modifier. Copper microparticles activated in nitric acid at a concentration 80 mmol dm-3 were applied at carbon felt by several techniques and in different parts of the felt, i.e. by stirring the felt in microparticles suspension, by dripping of the suspension to the part of the felt in contact with capillary (proximal), between two parts of the carbon felt (sandwich) and at a part of the carbon felt in contact with electrolyte in a measuring cell (distal). Electrodes modified in the distal and in the sandwich arrangement were chosen as the best ones. In the last part, calibration dependences for phenylalanine in concentration range from 0.025 mmol dm-3 to 1.0 mmol dm-3 were measured on the last two electrodes....
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Voltammetric Determination of Sudan I on Silver Solid Amalgam Electrode
Kadeřábková, Marta ; Fischer, Jan (advisor) ; Schwarzová, Karolina (referee)
The subject of this thesis was the development of method for determination of azo dye Sudan I (1-phenylazo-2-naphtol, CAS# 842-07-9) which is used in industry but it is undesirable in food products. The technique of differential pulse voltammetry (DPV) was used on a silver solid amalgam electrode modified by mercury meniscus (m-AgSAE) in 50 % methanol and Britton-Robinson (BR) buffer pH from 2 to 12 supporting electrolyte. Optimal conditions for Sudan I determination were in 50 % methanol and BR buffer pH 4,0, in which it was possible, without the need to regenerate the working electrode surface, to perform repeated measurements. Linear calibration of the substance was obtained in the range 1∙10-6 -1∙10-5 mol∙l-1 and 1∙10-5 -1∙10-4 mol∙l-1 . Limit of quantification was 6,2∙10-7 mol∙l-1 . Subsequently, usability of developed method was tested on samples containing Sudan I and food colorant Sunset Yellow (in the range from 1∙10-6 to 1∙10-5 mol∙l-1 ), but the method for these two analytes was not selective enough.
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