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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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Transparent boron-doped diamond electrode (t-BDDE) for spectroelectrochemistry
Lušpai, K. ; Keszeliová, D. ; Barlog, M. ; Petrák, Václav
In this work we have studied the properties of high quality boron-doped diamond layers prepared on transparent substrate and their use as working electrode for EPR/UV-VIS-NIR spectroelectrochemistry. Final goal of this work is to benefit from the wide potential window of boron-doped diamond electrodes even in the field of the EPR/UV-VIS-NIR spectroelectrochemistry. The studied electrodes are compatiable with UV-VIS-NIR measurements. Spectral background is stable within the whole electrochemical window. Some of the electrodes, with lower doping level, are also compatible with EPR spectroscopy. In this work, the electrodes and their properties are presented and usability is demonstrate by the spectrochemistry on real sample.
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Transparent boron-doped diamond electrode (t-BDDE) for spectroelectrochemistry
Lušpai, K. ; Keszeliová, D. ; Barlog, M. ; Petrák, Václav
In this work we have studied the properties of high quality boron-doped diamond layers prepared on transparent substrate and their use as working electrode for EPR/UV-VIS-NIR spectroelectrochemistry. Final goal of this work is to benefit from the wide potential window of boron-doped diamond electrodes even in the field of the EPR/UV-VIS-NIR spectroelectrochemistry. The studied electrodes are compatiable with UV-VIS-NIR measurements. Spectral background is stable within the whole electrochemical window. Some of the electrodes, with lower doping level, are also compatible with EPR spectroscopy. In this work, the electrodes and their properties are presented and usability is demonstrate by the spectrochemistry on real sample.
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Voltammetric and Amperometric Determination of Nitrophenols Using Boron-Doped Diamond Film Electrode
Karaová, Jana ; Barek, Jiří (advisor) ; Šelešovská, Renáta (referee) ; Jaklová Dytrtová, Jana (referee)
Presented Ph.D. Thesis is focused on the use of the boron-doped diamond (BDD) electrodes for voltammetric and amperometric determination of selected nitrophenols: 2-nitrophenol (2NP), 4-nitrophenol (4NP), and 2,4-dinitrophenol (2,4DNP). These compounds are listed as "priority pollutants" by United States Environmental Protection Agency (US EPA) due to their negative impact on living organisms and are mainly used in agriculture as plant growth stimulators. BDD electrodes are used for determination of wide range of electrochemically both reducible and oxidisable organic compounds and have become a popular electrode material thanks to its commercial availability and excellent mechanical and electrochemical properties. A differential pulse voltammetric method was developed for the determination of 2NP, 4NP and 2,4DNP at a BDD film electrode using electrochemical reduction and of 4NP and 2,4DNP using electrochemical oxidation. The method was successfully applied for the direct determination of these compounds in drinking and river water in the concentration range from 4×10-7 to 2×10-5 mol.L-1 . To improve the limit of quantification, a preconcentration by solid phase extraction from 100 mL (drinking and river water) and 1000 mL (drinking water) of water samples was used with limit of determination...
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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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Boron-doped diamond electrodes: Utilization for determination of reducible organic compounds
Vosáhlová, Jana ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
In this study the possibilities of utilization of boron-doped diamond (BDD) electrodes for electrochemical reduction of organic compounds and their determination in aqueous media were investigated. For this purpose BDD electrodes have several advantages (relative wide potential window in cathodic region, low sensitivity towards oxygen evolution) but are not frequently used. For the study were selected biologically active organic compounds with typical reducible groups. Vanillin (natural essential oil, synthetic aroma; reducible aromatic aldehyde) is not reducible at BDD electrode. Azidothymidine (antiviral drug; reducible azido group) shows voltammetric signal in Britton -Robinson buffer at pH 6.0 - 8.0, but its analytical utilization is difficult due to the close positioning to the decomposition of the supporting electrolyte. The height and potential of the reduction signal of 5-nitroquinoline (environmental pollutant; reducible nitro group on the aromatic nucleus and at higher potentials reducible heterocycle) is significantly influenced by the boron concentration in BDD film. Reduction of quinoline skeleton is visible in the range of pH6.0 - 11.0 in BR buffer. For differential pulse and DC voltammetry (reduction of nitro group) in BR buffer pH 5.0 limits of detection 0.2 µmol.l-1 and 2.7...
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Voltammetric determination of clinical markers vanillylmandelic and homovanillic acid at boron-doped diamond electrode
Baluchová, Simona ; Schwarzová, Karolina (advisor) ; Zima, Jiří (referee)
This thesis investigates electrochemical oxidation of two main catecholamine metabolites vanillylmandelic and homovanillic acid at anodically oxidized boron-doped diamond electrode using voltammetric techniques. Their behavior in aqueous media depends on its pH value significantly; the highest and best developed voltammetric signals are provided in an acidic medium when both organic compounds occur in their non-ionized form. The phosphate buffer pH 3.0 was chosen as supporting electrolyte for analysis of these two substances and the conditions of determination were optimized. Calibration dependences are linear for both studied compounds in the concentration range from 4 to 100 μmol∙l−1 . Using differential pulse voltammetry limits of detection for homovanillic acid (LOD = 0.57 μmol∙l−1 ) and for vanillylmandelic acid (LOD = 0.41 μmol∙l−1 ) were achieved. The possibility of their simultaneous determination at boron-doped diamond was also verified. The oxidation mechanisms of homovanillic acid and vanillylmandelic acid at boron-doped diamond electrode were studied by cyclic voltammetry and in both cases it is diffusion-controlled reaction.
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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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