|
|
Polarographic and Voltammetric Determination of Fomesafen
Maška, Jan ; Barek, Jiří (advisor) ; Fischer, Jan (referee)
The work is related to the polarographic and voltammetric determination of Fomesafen on the basis of its cathodic reduction using classical dropping mercury electrode (DME), hanging mercury drop electrode (HMDE) and non-traditional mercury meniscus modified silver solid amalgam electrode (m-AgSAE). Silver solid electrode (AgSAE) was developed as an alternative to mercury electrodes regarding legislative complications limitating usage of mercury because of its supposed toxicity. Properties of this electrode are very similar to the ones of mercury electrodes, mainly outstandingly broad cathodic potential region but excelent sensitivity either. As an electrode material, silver amalgam was used which non-toxicity is obvious given for example even by its long-term usage in stomatology as a main item for production of tooth-fillings. For model determination, Fomesafen was chosen because of its previous and sometimes also present usage as a major component of herbicid agents in agriculture. Its factual toxicity was actually proven and it was also classified as a potential carcinogen for humans. Historically, its usage was relatively deliberately massive, significant was e.g. in USA, but presently it was already forbidden in many countries. The intention of the work was to compare the analytical qualities...
|
|
| |
|
| |
|
|
Electrochemical Biosensors and Detectors Based on Silver Solid Amalgam for Analysis in Flow Systems
Josypčuk, Oksana ; Barek, Jiří (advisor) ; Vytřas, Karel (referee) ; Ludvík, Jiří (referee)
In this Ph.D. thesis new possibilities of using amalgam electrodes are presented. First of all, the tubular detector based on silver solid amalgam (TD-AgSA) was designed for determination of reducible compounds in flow systems. It was tested on model solutions of Cd2+ , Zn2+ and 4-nitrophenol in amperometric mode under conditions of flow injection analysis. Results have shown that developed tubular detector is simple and low cost device suitable for detection of reducible compounds with good sensitivity, repeatability and long-term stability (at least 2 years) with possibility to work at potentials up to 2 V in aqueous solutions. Afterwards, this newly developed detector was successfully used for the determination of an active ingredient lomustine in pharmaceutical preparation CeeNU® Lomustine by non-stop-flow differential pulse voltammetry based on reduction of present nitroso group. For measurements in the flow system miniature reference electrodes saturated calomel electrode, mercury-mercurous sulfate, and mercury-mercuric oxide electrode based on paste silver solid amalgam were fabricated and tested for 14 months. The calomel electrode based on paste silver amalgam proved to be the most resistant to polarization and it was used in all experiments in this thesis. Next, the electrochemical...
|
|
|
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...
|
|
|
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...
|
|
|
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...
|
guest ::
RSS feed.