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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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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 Boron Doped Diamond Electrode for Determination of 5-hydroxyindoleacetic Acid
Hrdlička, Vojtěch ; Navrátil, Tomáš
A new method for voltammetric determination of clinical biomarker 5-hydroxyindoleacetic\nacid (HIAA) at the boron-doped diamond electrode (BDDE) was developed. Anodically and\ncathodically pretreated BDDEs were tested in the pH ranges from 1 to 12, pre-treatment at\n+2.0V/60 s, and pH 3 was found to be the optimum.\nThe optimum square wave voltammetry (SWV) parameters were: f = 12 Hz, amplitude 60\nmV, and potential step 4 mV. SWV concentration dependency was constructed in the range\nfrom 0.1 to 100 μmol L−1, limits of determination and detection were 0.3 and 0.1 μmol L−1,\nrespectively. HIAA oxidation electrode process at BDDE was diffusion-controlled, as\nuncovered by cyclic voltammetry. Interestingly, HIAA peak potential was constant in various\nranges of pH, indicating a non-Nernstian behavior at the BDDE, in contrast to a previously\npublished electrooxidation mechanism consisting of a coupled H+/e− transfer.
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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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Novel Approaches in Electrochemical Determination of Xenobiotic Compounds and in Study of Their Interaction with DNA
Hájková, Andrea ; Vyskočil, Vlastimil (advisor) ; Trnková, Libuše (referee) ; Labuda, Ján (referee)
Presented Ph.D. Thesis is focused on the development of analytical methods applicable for determination of selected xenobiotic compounds and for monitoring DNA damage they can induce. The main attention has been paid to the development and testing of non-toxic electrode materials for preparation of miniaturized electrochemical devices and novel electrochemical DNA biosensors. 2-Aminofluoren-9-one (2-AFN) was selected as a model environmental pollutant, which belongs to the group of hazardous genotoxic substances. Its carcinogenic and mutagenic effects may represent a risk to living and working environment. 2-AFN has one oxo group, where the cathodic reduction occurs, and one amino group, where the anodic oxidation occurs. The voltammetric behavior of 2-AFN in the negative potential region was investigated at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE) representing a non-toxic and more mechanically robust alternative to mercury electrodes. This working electrode was subsequently used for the development of a newly designed miniaturized electrode system (MES), which has many benefits as the possibility of simple field measurements, easy portability, and the measurement in sample volume 100 µL. Moreover, a glassy carbon electrode (GCE) was used for further investigation of...
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Factors influencing electrochemical oxidation of m-cresol at boron-doped diamond electrode
Procházková, Kateřina ; Schwarzová, Karolina (advisor) ; Vyskočil, Vlastimil (referee)
This study investigates electrochemical oxidation of m-cresol on boron-doped diamond electrode using direct current voltammetry (DCV), differential pulse voltametry (DPV) and cyclic voltammetry (CV). In aqueous media in pH range 2.0 - 12.0 m-cresol provides one oxidation peak. The electrode reaction is diffusion-controled. Because of electrode passivation two types of pretreatment were applied for reactivation of electrode surface., i.e. alumina polishing and anodic activation using potential of +2400 mV. Peak heights and potentials are strongly dipending on the type of pretreatment for DCV and DPV - the difference in peak potentials can reach 430 mV. Using optimal conditions for alumina polishing in 0.01 μmol·L-1 NaOH the linear dynamic range is 1.0 - 75 μmol·L-1 for DCV and 0.75 - 75 μmol·L-1 for DPV. And for anodic activation in BR buffer pH 2.0 the linear dynamic range is 0.75 - 75 μmol·L-1 for DCV and DPV. The influence of boron-doping level was investigated using a semiconductive and mettalic-type BDD film. For the latter the sensitivity in DP voltammetry is two times higer and for both types the linear dynamic range is ca 1 - 25 μmol·L-1 . The voltammetric response of m-cresol was further investigated in the presence of cationic surfactants. In the presence of CTAB and CPB the peak current...
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A new approach to the electroanalysis of primary bile acids and related steroids
Klouda, Jan
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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Novel Approaches in Electrochemical Determination of Xenobiotic Compounds and in Study of Their Interaction with DNA
Hájková, Andrea
Presented Ph.D. Thesis is focused on the development of analytical methods applicable for determination of selected xenobiotic compounds and for monitoring DNA damage they can induce. The main attention has been paid to the development and testing of non-toxic electrode materials for preparation of miniaturized electrochemical devices and novel electrochemical DNA biosensors. 2-Aminofluoren-9-one (2-AFN) was selected as a model environmental pollutant, which belongs to the group of hazardous genotoxic substances. Its carcinogenic and mutagenic effects may represent a risk to living and working environment. 2-AFN has one oxo group, where the cathodic reduction occurs, and one amino group, where the anodic oxidation occurs. The voltammetric behavior of 2-AFN in the negative potential region was investigated at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE) representing a non-toxic and more mechanically robust alternative to mercury electrodes. This working electrode was subsequently used for the development of a newly designed miniaturized electrode system (MES), which has many benefits as the possibility of simple field measurements, easy portability, and the measurement in sample volume 100 µL. Moreover, a glassy carbon electrode (GCE) was used for further investigation of...
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A new approach to the electroanalysis of primary bile acids and related steroids
Klouda, Jan
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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