National Repository of Grey Literature 104 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
New approaches for voltammetric determination of tumour biomarkers and antidotes in urine
Hrdlička, Vojtěch ; Barek, Jiří (advisor) ; Novotný, Ladislav (referee) ; Skopalová, Jana (referee)
This Ph. D. thesis presents new methods for the determination of selected clinically relevant electrochemically active compounds. The first part deals with development of determination of tumour biomarkers homovanillic acid (HVA) and vanillylmandelic acid (VMA) in human urine with the use of hollow-fibre based liquid-phase microextraction (HF-LPME) and differential pulse voltammetry (DPV) at cathodically pre-treated boron doped diamond electrode (BDDE). Optimum conditions for HF-LPME-DPV of HVA and VMA were as follows: butyl benzoate as supported liquid membrane formed on porous polypropylene hollow-fibre, 0.1 mol L−1 HCl as donor phase and 30 min extraction time. Optimum acceptor phases were 0.1 mol L−1 phosphate buffer of pH 6 with ionic strength set to 0.55 mol L−1 for HVAand 0.1 mol L−1 NaOH for VMA, respectively. HF-LPME-DPV concentration dependencies for HVA and VMAwere linear in the range from 0.4 to 100 µmol L−1 and 0.5 to 100 µmol L−1 . Limits of quantification (LOQ)/detection (LOD) were 1.2/0.4 µmol L−1 for HVA and 1.7/0.5 µmol L−1 for VMA, respectively. The applicability of the developed methods was verified by analysis of human urine. In the second part, voltammetric behaviour of heavy metal poisoning antidote 2,3- dimercapto-1-propane-sulfonic acid (DMPS) was investigated with the use...
Voltammetric and amperometric determination of homovanillic, vanillylmandelic, and 5-hydroxyindole-3-acetic acid
Němečková, Anna ; Barek, Jiří (advisor) ; Labuda, Ján (referee) ; Skopalová, Jana (referee)
Presented dissertation thesis is focused on the development of electrochemical methods for the determination of three important tumour biomarkers, namely homovanillic acid (HVA), vanillylmandelic acid (VMA), and 5-hydroxyindole-3-acetic acid (5-HIAA). First part of the study is focused on electrochemical behaviour of these analytes in batch arrangement using differential pulse voltammetry (DPV) at screen-printed carbon electrodes (SPCEs). It has been proved that presented method is sufficiently sensitive for monitoring above mentioned analytes. Moreover, it can be used for determination of HVA and VMA in mixture. Obtained limits of detection (LODs) were 0.24 µmol·L-1 for HVA, 0.06 µmol·L-1 for VMA, and 0.12 µmol·L-1 for 5-HIAA. The requirements to speed up the analysis and at the same time to reduce its price initialized our study of the determination of tested biomarkers in flow systems. Firstly, flow injection analysis with amperometric detection was investigated for the determination of all three biomarkers at the same SPCE, and then an analogous determination of structural more similar pair, HVA and VMA, was performed at a boron doped diamond electrode (BDDE). Obtained LODs of optimized methods were as follows: at SPCE 0.07 µmol·L-1 for HVA, 0.05 µmol·L-1 for VMA, and 0.03 µmol·L-1 for 5-HIAA,...
The Use of New Types of Carbon Electrodes for Voltammetric Determination of Organic Compounds
Birhanzlová, Tereza ; Barek, Jiří (advisor) ; Labuda, Ján (referee) ; Ludvík, Jiří (referee)
This Ph.D. thesis is focused on the use of a new type of non-toxic electrode (carbon film electrode - CFE) for voltammetric determination of environmental organic pollutants and on the development and use of a new type of solid electrode modified with carbon nanotubes for the determination of 2-nitrophenol (2-NP) and 8-nitroquinoline (8-NQ). The work is a continuation of the previous study of 5- nitroquinoline (5-NQ) using CFE in author's bachelor and diploma thesis. The determination of 5-NQ based on anodic oxidation is not possible at CFE and thus 2-NP was chosen as a model substance for voltammetric determination in both regions of potential window (cathodic and anodic). Further attention was paid to the development of a new type of carbon electrode with surface containing carbon nanotubes and its application for the determination of 8-NQ using differential pulse voltammetry (DPV) based on cathodic reduction of present nitro group. Silver solid electrode (AgE) as a substrate electrode for following modification was used. At first, the AgE itself was used for determination of 8-NQ in deionized water and in model samples of drinking and river water. Then the possibility of electrode surface modification using different type of carbon nanotubes was investigated. The AgE modified with carboxylated...
Development of electrochemical methods for study of antibacterial compounds in small volumes
Gajdár, Július ; Barek, Jiří (advisor) ; Šiškanova, Tatiana (referee) ; Labuda, Ján (referee)
Main goal of this Ph.D. thesis is to develop voltammetric methods for the electrochemical study of novel antimycobacterial compounds hydroxynaphthalene- carboxamides. Firstly, this study was focused on the miniaturization of voltammetric methods and construction of an electrochemical microcell due to usually small volume of samples that are associated with an analysis of biologically active compounds in biological matrices. Therefore, all aspects of the voltammetric procedure were studied in a relation to miniaturization. Microcells were based on commercially available electrodes: glassy carbon electrode as a reliable electrode material with well-described characteristics and a novel silver solid amalgam electrode. This study was carried out with analytes 4-nitrophenol, pesticide difenzoquat, and 1-hydroxy-N-(4-nitrophenyl)naphthalene-2-carboxamide. Attention was paid especially to the optimization of oxygen removal procedures in the drop of a solution. Developed miniaturized methods had the same parameters for the determination of studied compounds as in bigger volumes. The proposed electrochemical microcell can be generally used for voltammetric analysis of those samples of biological or environmental origin that are usually available in very limited volumes. Second part of the thesis was focused...
Miniaturized boron doped diamond film electrode for neuroblastoma biomarkers determination
Hrdlička, Vojtěch ; Barek, J. ; Navrátil, Tomáš ; Taylor, Andrew
Cathodically pretreated miniaturized boron doped diamond film electrodewas successfully tested for the purposes of in-situ determination of neuroblastoma biomarkers after hollow-fibre based microextraction. Electrode was tested using K-3[Fe(CN)(6)] and vanillyl-mandelic acid as model substances. Limits of detection and determination are 2.2 and 6.6 mu mol L-1, respectively. Linear range was 2.2-100 mu molL(-1), repeatability 1.34% (n = 10).
Development of Novel Electrochemical Methods Using Various Membrane Materials for Monitoring of Selected Anticancer Drugs and Phytochelatins
Skalová, Štěpánka ; Barek, Jiří (advisor) ; Labuda, Ján (referee) ; Trnková, Libuše (referee)
Present Ph.D. Thesis is focused on the development of electrochemical methods for determination of anticancer drugs using various types of membranes for their preliminary separation. Furthermore, this Thesis reports the study of transport mechanisms of heavy metals in the presence of phytochelatins across biological membranes. Sodium anthraquinone-2-sulphonate (AQS) was used as a model compound for its similar structure with anthraquinone-based (AQ-based) anticancer drugs (doxo/daunorubicin) and also due to its better availability. All these compounds can be easily electrochemically oxidized and/or reduced. Redox behaviour of AQS was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in a cathodic region on mercury meniscus modified (m-AgSAE) and polished silver solid amalgam (p-AgSAE) electrodes, Obtained results were used for the development of a micro-volume voltammetric cell (MVVC). Its applicability for voltammetric determination of anticancer drugs was verified by using doxorubicin (DX) as a model substance. The second part of this Thesis deals with therapeutic monitoring of anticancer drugs in the blood circulation of the patients. For pilot experiments, a liquid-flow system with dialysis catheter and amperometric detection was used. The flow rate of carrier...
Voltammetric determination of 1-hydroxy-N-(4-nitrophenyl)naphthalene-2-carboxamide by voltammetry at a glassy carbon electrode in microvolumes of dimethyl sulfoxide
Gajdar, J. ; Goněc, T. ; Jampílek, J. ; Brázdová, Marie ; Bábková, Zuzana ; Fojta, Miroslav ; Barek, J. ; Fischer, J.
Voltammetric reduction and oxidation of 1-hydroxy-N-(4-nitrophenyl) naphthalene-2-carboxamide was investigated at glassy carbon electrode in dimethyl sulfoxide. Cyclic voltammetry was used to investigate the mechanism of reduction of nitro group and oxidation of hydroxyl group. The analyte was successfully determined in dimethyl sulfoxide by differential pulse voltammetry and the whole voltammetric procedure was miniaturised. Square wave voltammetry was employed to reduce the interference from dissolved oxygen. Determination in one drop (20 mu L) of 0.1 mol L-1 tetrabutyl-ammonium tetrafluoroborate in dimethyl sulfoxide provided very similar results compared to determination in the bulk solution. Limits of quantification were 5.0 mu mol L-1 for cathodic voltammetry and 5.3 mu mol L-1 for anodic voltammetry.
Voltammetry of 1-Hydroxy-N-(4-nitrophenyl)naphthalene-2-carboxamide at a Glassy Carbon Electrode
Gajdar, J. ; Goněc, T. ; Jampílek, J. ; Brázdová, Marie ; Bábková, Zuzana ; Fojta, Miroslav ; Barek, J. ; Fischer, J.
This electrochemical study is aimed at an investigation of a reaction mechanism and determination of 1-hydroxy-N-(4-nitrophenyl)naphthalene-2-carboxamide in media with various amount of an organic solvent (dimethyl sulfoxide or methanol). The studied analyte is a model substance from a group of recently prepared drugs with antibiotic characteriss Mechanism of reducible nitro group and oxidisable hydroxyl group is compared with studies of substructures and structurally similar compounds. Preliminary comparison of different media was carried out to find the best parameters for the determination.
Voltammetric Techniques for Analysis in a Single Drop of a Solution
Gajdar, J. ; Goněc, T. ; Jampílek, J. ; Brázdová, Marie ; Bábková, Zuzana ; Fojta, Miroslav ; Barek, J. ; Fischer, J.
This contribution describes miniaturization of voltammetric methods and some of the main problems caused by reducing the sample volume to 20 mu L. This study was carried out in dimethyl sulfoxide solutions and buffered aqueous solutions with 10% DMSO at a glassy carbon electrode. A novel antibiotic agent, 1-hydroxy-N-(4-nitrophenyl) naphthalene-2-carboxamide, was used as a model substance. This analyte was determined by cathodic and anodic voltammetry. Elimination of the negative influence of dissolved oxygen was performed in various manners. Two most effective methods were square wave voltammetry that can be used in the presence of dissolved oxygen and removal of oxygen in a microcell with nitrogen atmosphere inside.
Determination of a Novel Antimycobacterial Agent in a Single Drop of a Solution by Voltammetry at a Glassy Carbon Electrode
Gajdar, J. ; Goněc, T. ; Jampílek, J. ; Brázdová, Marie ; Bábková, Zuzana ; Fojta, Miroslav ; Barek, J. ; Fischer, J.
One of the novel antimycobacterial agents from the group of hydroxynaphthalene carboxamides (namely I-hydroxy-X-(4-nitrophenyl)naphthalene-2-carboxamide) was investigated using voltammetric methods for the first time. The study was carried out at a glassy carbon electrode by methods of cathodic and anodic differential pulse voltammetry in micro volumns (20 mu L) of an aqueous solution at pH 7 containing 10% dimethyl sulfoxide and in a real matrix of a bacterial growth medium. The miniaturized method was compared with the macro volume determination. The presence of oxygen in micro volumes presents the biggest obstacle for the miniaturized method.

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See also: similar author names
6 Barek, J.
2 Barek, Jan
2 Barek, Jaroslav
1 Barek, Jiří
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