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Optimization of anodic and cathodic pre-treatments of boron doped diamond electrode surfaces for electroanalysis
Baudisová, Kateřina ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
This bachelor thesis deals with the optimization of anodic and cathodic pretreatment of BDD electrodes and subsequent comprehensive characterization and comparison of electrochemical parameters of unmodified, O-terminated and H-terminated BDD electrodes. The study was carried out using cyclic voltammetry of two model inner sphere redox systems [Fe(CN)6]4−/3− and dopamine/dopamine-o-quinone. Boron concentrations in the BDD films ranged from 500 ppm to 8000 ppm. O-termination of the electrode surface was most effectively achieved when an activation potential of Eakt = +3.0 V was inserted for 10 min into 0.5 mol l−1 H2SO4. For the dopamine/dopamine-o-quinone system, the O-terminated BDD electrodes caused deceleration of electron transfer compared to the unmodified BDD electrodes, which was accompanied by an increase in the potential difference with the highest ΔEp at 500 ppm BBD electrode (ΔEp = 711 mV). To achieve the H-terminal surface, single and cumulative reduction was tested by inserting Eakt = −3.0 V. A sufficient single reduction time for the [Fe(CN)6]4−/3− system was determined to be 60 s, whereas in the case of dopamine, the electrochemical parameters did not stabilize at the selected reduction times, but the cathodic and anodic peak signal at the H-terminated 1000 ppm BDD electrode was up...
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Amperometric determination of selected neurotransmitters using porous boron-doped diamond electrode
Vikartovský, Andrej ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
In this work, electrochemical behaviour of porous BDD electrode was observed during the determination of dopamine (DA) and norepinephrine (NE) using flow methods. For the separation of analytes isocratic elution with Britton-Robinson buffer of pH 6,0 was used as mobile phase, with flow rate 1 ml∙min−1. Separation column Kinetex® EVO C18 (150 × 4,6 mm). was used as reversed stationary phase. Porous BDD electrode was used for detection with applied electrical potential 1,1 V and UV detection with wavelenght 280 nm. Dependence of the signal on the concentration of analytes was observed for both detectors in the concentration range from 1∙10−6 to 4∙10−4 mol∙dm−3. Limits of detection, limits of quantification and linear dynamic ranges were determined. To determine stability of porous BDD electrode, repeatability with concentration of analytes 1∙10−4 mol∙dm−3 was measured as well as reproducibility after 4 and 6 weeks with same condition of measurement.
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The width of potential window of boron doped diamond electrodes in dependence on their pretreatment and composition of the mixed electrolyte solution
Dvořáková, Klára ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The diploma thesis focuses on the range of the potential window of the BDD electrode in dependence on the composition of the mixed electrolyte solution and the treatment of the electrode surface. The measurements were performed on a polished (p-BDD) and O-terminated (O-BDD) electrode by the method of linear sweep voltammetry (LSV) in a three-electrode system. It was confirmed that in an environment with a suitable organic solvent, the range of the potential window widens. The measured solutions consisted of deionized water containing sodium perchlorate with a concentration of 1 mmol l−1 and one organic solvent in which sodium perchlorate with a concentration of 1 mmol l−1 was also dissolved. Acetonitrile, methanol, N,N-dimethylformamide and isopropanol were used in solutions (0 %, 1 %, 5 %, 10 %, 50 %, 70 %, 90 %, 95 %, 99 % or 100 % volume percent). Expansion, or the shortening of the potential window range was evaluated separately for each solvent in the anodic and cathodic regions. The expansion of the window on both sides was confirmed in acetonitrile as the concentration of the solvent increases, so it is based on this experiment as a universal solvent suitable for the determination of reducing and oxidizing analytes, from measurements on O-BDD and also on p-BDD. In the case of the remaining...
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Comparison of the gold microelectrode and conventional electrode for the saccharide determination using pulsed amperometry
Smítková, Karolína ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
This bachelor's thesis deals with combination of pulsed amperometric detection (PAD) with flow injection analysis (FIA) in order to use them to detect glucose and consequently carbohydrates in solution. Pulsed amperometry is efficient detection method for many of organic compounds in which, as the name suggests, a sequence of three or four potential pulses is applied at the working electrode. If the pulse parameters are suitable, then it is possible to eliminate the unwanted passivation of the working electrode due to the adsorption of oxidation products and intermediate products of aliphatic compounds, which would lead to a reducion of its active surface. The aim od this work is to show the effect of the change of the value of the applied potential pulses on the peak heights corresponding to the oxidation of the glucose in solution and to evaluate their repeatability. As a working electrode, it compares a gold electrode of conventional size and a gold microelectrode. The determination was performed in a borate buffer with pH = 10. First of all, cyclic voltammograms of solution with concentration of glucose 1·10-2 mol dm-3 were measured to obtain the initial values of the applied pulses. Subsequently, the dependence of the peak heights on their injection order for different values of individual...
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Electrochemical properties of synthetic drugs 3-fluorophenmetrazine and 4-methylpentedrone
Jiroušková, Eliška ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The aim of this Thesis was to clarify electrochemical properties of two new psychoactive substances. These substances are an alternative to classical drugs because they are not controlled by current legislation. It is important to determine the metabolites of these substances to be able to detect them in organism. Their electrochemical properties could explain the process of the first phase of biotransformation in human organism. Two synthetic stimulants were studied - 3-fluorophenmetrazine and 4-methylpentedrone, used as substitutes for cocaine or ecstasy. The purity of substances was controlled by HPLC with UV/Vis diode array detector and the stability was verified by UV/Vis spectrophotometry. Electrochemical properties were studied in phosphate buffer using cyclic voltammetry. For both substances was calculated theoretical HOMO and LUMO spatial distribution. This information was important to estimate parts of molecules, that can be reduced or oxidised. The analytical method was developed on glassy carbon electrode using differential pulse voltammetry. Substance 3-fluorophenmetrazine was determined in phosphate buffer pH 9,0 with limit of detection of 5,1 µmol l-1 . The linear range of calibration curve is from 7,0 to 107,0 µmol/l, R = 0,9988. 4-methylpentedrone was determined in phosphate...
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Polarographic Determination of Genotoxic 2-Amino-9-fluorenone
Hájková, Andrea ; Vyskočil, Vlastimil (advisor) ; Dejmková, Hana (referee)
of Bachaleor Thesis The aim to this work was to find the optimum conditions for polarographic determination of genotoxic 2-amino-9-fluorenone (2-AFN) that can negatively affect the living and working environment. Foremost, the stability of 2-AFN stock solution in methanol was monitored using UV-VIS spectrophotometry and an optimal ratio of buffered aqueous and methanolic phase was found out for following polarographic measurements at a classical mercury dropping electrode (DME). The dependence of polarographic behavior of 2-AFN (of concentration 1×10-4 mol dm-3 ) on pH of analyzed solution was measured using DC tast polarography (DCTP) and differential pulse polarography (DPP) in the pH range 1.9 - 12.8, in the medium of Britton-Robinson (BR) buffer - methanol (9:1). The mechanism of polarographic reduction of electrochemically reducible oxo group at 2-AFN has been proposed on the basis of thus observed behavior. The optimum medium of BR buffer pH 4.0 - methanol (9:1) has been chosen for both polarographic techniques. The concentration range from 1×10-6 to 1×10-4 mol dm-3 was measured using DCTP at DME and from 1×10-7 to 1×10-4 mol dm-3 using DPP at DME. Reached limits of quantification (LQs) were 5×10-7 mol dm-3 and 1×10-7 mol dm-3 for DCTP at DME and DPP at DME, respectively. For comparison, the...
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Voltammetric Determination of Anticancer Drug Flutamide and Its Metabolite 4-Nitro-3-trifluoromethylaniline
Radová, Jitka ; Barek, Jiří (advisor) ; Dejmková, Hana (referee)
The subject of this Diploma Thesis has been the study of electrochemical behavior of anticancer drug flutamide (FLD) and one of its metabolites 4-nitro-3-trifluoromethylaniline (NTMA). The aim was to find and define the optimum conditions for the determination of both compounds at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE) and at a carbon film electrode (CFE) using DC voltammetry (DCV) and differential pulse voltammetry (DPV). This Diploma Thesis follows closely the Bachelor Thesis, defended at the Department of Analytical Chemistry, Faculty of Science, Charles University in Prague. In this Bachelor Thesis, a voltammetric determination of FLD using DCV and DPV at m-AgSAE has been described, with attained limits of quantification (LQs) 5.0·10-6 mol.dm-3 (for DCV) and 3.0·10-6 mol.dm-3 (for DPV). In presented Diploma Thesis, voltammetric behavior of NTMA has been studied in dependence on the pH of the medium of Britton-Robinson (BR) buffer-methanol (9:1). The optimum conditions have been found for the determination of this substance using DCV and DPV at m-AgSAE and CFE in the cathodic area. As the optimum media, BR buffer-methanol (9:1) of resulting pHf 8.3 (for both DCV and DPV at m-AgSAE) and of pHf 5.1 (for both DCV and DPV at CFE) have been chosen. Further, the LQs have...
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