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Utilization of complexation of tebuconazole with Cu(II) ions for its voltammetric detection
Dostálková, Lucie ; Fischer, Jan (advisor) ; Křížek, Tomáš (referee)
Tebuconazole is a triazole fungicide used in agriculture that can be present in the environment and have a negative effect on various organisms. Therefore, the electrochemical properties of tebuconazole and its complexation with Cu(II) ions on a boron doped diamond electrode were studied for its possible indirect detection in the presence of these ions. For the determination of Cu(II) ions, conditions in the concentration range 0.1-10 mol l-1 were optimized by differential pulse voltammetry in a 0.01 mol l-1 HNO3 environment on anodically oxidized BDDE, the limit of quantitation was 0.087 µmol l-1 . After optimization of the conditions, the indirect determination of tebuconazole was tested. The signal of free Cu(II) ions after the addition of tebuconazole was monitored. A decrease in this signal was observed and a linear calibration dependence could be measured for a decrease in the signal of 10 µmol l-1 Cu(NO3)2 in the concentration range of 2-10 µmol l-1 tebuconazole and for 1 µmol l-1 Cu(NO3)2 in the concentration range of 2-10 µmol l-1 and 10-100 µmol l-1 tebuconazole. Complexation of tebuconazole with Cu2+ was shown to occur almost instantaneously. Tebuconazole itself gives an anodic peak at a potential of +1550 mV in aqueous medium of 0.01 mol l-1 HNO3. Using differential pulse voltammetry,...
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Development of voltammetric methods for detection of cholesterol and its prekursor lathosterol
Bláhová, Eva ; Schwarzová, Karolina (advisor) ; Fischer, Jan (referee)
Cholesterol is an irreplaceable sterol found in animal cells, lathosterol is one of its precursors. The first aim of this Thesis is to develop a method for determining cholesterol after liquid- liquid extraction from milk matrices by differential pulse voltammetry on a boron doped diamond electrode in the presence of perchloric acid in acetonitrile where cholesterol provides an irreversible anodic response at the potential between +1300 and +1600 mV depending on the water content. The second aim is a study of the voltammetric behavior of lathosterol on boron doped diamond and glassy carbon electrodes using cyclic voltammetry and differential pulse voltammetry mainly in perchloric acid but also sodium perchlorate where lathosterol provides an irreversible anodic response at the potential of about +1650 mV on the boron doped diamond electrode and at the potential of +1350 mV on a glassy carbon electrode. The effect of other acids - sulfuric, nitric and phosphoric - on the response of lathosterol was also investigated. The influence of the water content in the measured solution and the influence of the polarization rate on the response of lathosterol were studied. Furthermore, the calibration dependence of lathosterol was measured using differential pulse voltammetry after optimization of its...
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Development of voltammetric methods for detection of phytosterols on carbon-based electrodes
Zelenský, Michal ; Schwarzová, Karolina (advisor) ; Fischer, Jan (referee)
The aim of this diploma thesis was to develop an electrochemical method for three phytosterols, namely stigmasterol β-sitosterol and ergosterol using voltammetry techniques on glassy carbon electrode and boron doped diamond electrode. The work builds on previous results, where it was shown that the electrochemical oxidation of phytosterols requires perchloric acid in acetonitrile. When this acid is used, a dehydration reaction occurs. Calibration dependences were measured here for all phytosterols in an environment with a water content of 0.43%. The stability of the signal with increasing distilled water content was further investigated. Then the calibration dependences in the increased water content were measured again. If we want to use HPLC-type separation techniques, we must first find out how the phytosterols will behave in this environment, and therefore the signal stability on the buffer content was investigated. The buffers used were phosphate and acetate buffer. Subsequently, the concentration dependence was measured in an environment with a higher content of phosphate buffer. Furthermore, the possibility of detecting two phytosterols at once was investigated. Key words: dehydration, glassy carbon electrode, boron doped diamond electrode, oxidation, phytosterols, voltammetry
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Development of electroanalytical methods for detection of bile acids possessing 7α hydroxyl group
Jelšíková, Kristýna ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
This master's thesis contains a study of electrochemical processes of selected bile acids possessing 7 hydroxyl group (cholic, chenodeoxycholic and −muricholic). The measurements were performed on boron−doped diamond electrode in the non-aqueous medium of acetonitrile and perchloric acid (water content 0.55 %) by cyclic voltammetry. It is known that the electrochemical activity of 7 bile acids is increased by a dehydration reaction between perchloric acid and the 7 bile acid. The subject of the study was the stability of the voltammetric response of chemically activated bile acids in the region of negative potentials. It was found that the presence of oxygen in the measured solution is an important factor for obtaining the cathodic signal of 7 bile acids. It probably performs a regenerative function; the product of the electrochemical reduction is re-oxidized in its presence, which leads to an increase in the voltammetric response. At the same time, it is important that the direction of the scan in cyclic voltammetry first proceeds to positive values. A potential of +2.0 V (vs. Ag/AgNO3 in acetonitrile) must be reached for the HO● radicals to be formed. It is these radicals that presumably lead to the formation of the product(s) of bile acids electrochemical oxidation that can be subsequently...
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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,...
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Electrochemical oxidation of selected bile acids in acetonitrile
Habániková, Shannelle Diana ; Schwarzová, Karolina (advisor) ; Fischer, Jan (referee)
The concentration of bile acids is an important parameter in hepatobiliary tract diseases. This work deals with the electrochemical oxidation of the chenodeoxycholic (CDCA) and cholic acid (CA) at boron dopped diamond (BDD) electrode in comparison with the oxidation at glassy carbon (GCE) and platinum electrode (PtE), in a mixed environment of acetonitrile and water (0.26 % from 0.1 mol·l-1 HClO4, supporting electrolyte). The measurement was carried out in an electrochemical cell with salt bridge containing 0.5 mol·l-1 NaClO4 separating the working and the Pleskov's reference electrode (0.01 mol·l-1 AgNO3 and 1 mol·l-1 NaClO4 in acetonitrile). Cyclic voltammetry (CV) characterization of BDD electrode by a redox pair [Fe(CN)6]4-/3- (c = 0.1 mmol·l-1) in 1 mol·l-1 KCl was performed. Quasi-reversible behaviour was observed and the difference of the anodic and the cathodic peak potential ranged from 80 to 200 mV, depending on the scan rate. Alumina polishing (4 min) of the BDD electrode was identified as the most appropriate method of activating the surface and it was applied between consecutive voltammetric scans in the presence of CA and CDCA. Irreversible anodic peaks of CDCA and CA in acetonitrile-water (0.26 %) were observed at the relatively high potentials of about +1100 ± 100 mV, depending on...
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Voltammetric detection of stigmasterol at boron-doped diamond electrode in mixed media
Benešová, Lenka ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
V o l t a m m e t r i c d e t e c t i o n o f s t i g m a s t e r o l a t b o r o n d o p e d d i a m o n d e l e c t r o d e i n m i x e d m e d i a L e n k a B e n e š o v á Univerzita Karlova v Praze Přírodovědecká fakulta Praha 2015 Abstract The aims of the study thesis was to suggest suitable solvent for oxidation of stigmasterol on boron doped diamond electrode. Cyclic voltammetry in mixed media of water and organic solvents was used for this purpose. First of all, the effect of organic solvent on potential window of boron doped diamond electrode was studied. Solvents used were methanole, isopropanole, N-dimethylformamide and acetonitrile; the water components was phosphate buffer (0,075 mol.l-1, pH 3,0). It was deduced from the results, that suitable solvent for detection of stigmasterol on was the acetonitrile, which provided sufficiently large potential window in anodic area. Keywords: boron doped diamond electrode, cyclic voltammetry, organic solvent, oxidation, stigmasterol
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Study of electrochemical behaviour of quinine and cinchonidine at boron doped diamond electrode
Brunovská, Veronika ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
In this thesis, it was for the first time studied the electrochemical behaviour of cinchona alkaloids quinine and cinchonidine by cyclic voltammetry and differential pulse voltammetry using boron doped diamond (BDD) thin film as an electrode material. Cyclic voltammograms did not exhibit any significant anodic signals corresponding to a simple electrode reaction. However, current increase with indistinctive maxima compared to the basic electrolyte was recorded in Britton - Robinson buffers with pH 2,0 − 12,0 medium. Accordingly, insignificant signals observable in the cathodic area at far negative potential close to the potential of decomposition of the supporting electrolyte , presumably to the reduction of quinoline skeleton. It was found by means of differential pulse voltammetry that the number of those observable current maxima varies for quinine and cinchonidine in different supporting electrolytes. Quinine provided the best developed anodic peaks in the medium of BR buffer pH 5,0 and 6,0 and cinchonidine in pH 7,0, 9,0 and 12,0. The calibration dependence of anodic peak of quinine in BR buffer pH 5,0 is linear in the concentration range 6∙10−6 mol∙l−1 − 1∙10−4 mol∙l−1 with limit of quantitation 4,39∙10−6 mol∙l−1 . In the cathodic area the limit of quantitation is 4,33∙10−5 mol∙l-1 . The...
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Voltammetric determination of homovanillic acid at boron doped diamond electrode for hollow fibre microextraction
Hrdlička, V. ; Barek, J. ; Navrátil, Tomáš
Presented work deals with hollow-fibre assisted liquid/liquid/liquid microextraction (HF-LPME) and subsequent voltammetric detection of clinical biomarker homovanillic acid (HVA). Three main areas are discussed: hollow fibre assisted extraction of HVA, voltammetric detection of HVA under basic conditions, and sensing in very small volumes. Using HF-PLME, HVA was extracted with 1-octanol as a supported liquid membrane with enrichment factor of 55 after 60 minutes of extraction. A novel method of miniaturized voltammetric determination of HVA using cathodically pretreated boron doped diamond electrode was also developed. Using differential pulse voltammetry, limit of detection, limit of quantificati was 1.9 mu mol dm(-3) on 6.6 mu mol dm(-3).
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Lab-made Sensors Based on Boron-doped Diamond for Determination of Herbicide Linuron
Štěpánková, M. ; Šelešovská, R. ; Janíková, L. ; Vojs, M. ; Marton, M. ; Behúl, M. ; Nováková, Kateřina ; Chýlková, J.
Voltammetric behaviour of substituted urea herbicide linuron (LIN) was investigated using two types of boron-doped diamond electrodes (BDDE): commercial BDDE and lab-made sensors based on boron-doped diamond (LM-BDDE). Various methods like cyclic voltammetry (CV), direct current voltammetry (DCV) and differential pulse voltammetry (DPV) were examined. It was found that LIN provides one oxidation peak using all of the tested working electrodes and the highest current response was recorded in the acidic media. Thus, Britton-Robinson (B-R) buffer of pH 2 was used as a supporting electrolyte. Parameters of DPV were optimized and the low limits of detection (LOD) were reached 1.41×10−7 M for commercial boron-doped diamond electrode and 8.81×10−9 M, respectively, which represents the lowest LOD obtained for lab-made boron-doped diamond electrodes.
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