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Voltammetric determination of pesticides using meniscus modified silver solid amalgam electrode
Gajdár, Július ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
The aim of this bachelor thesis is to find the optimal conditions for voltammetric determination of pesticides cypermethrin, deltamethrin and difenzoquat on meniscus modified silver solid amalgam electrode using differential pulse voltammetry. Conditions under which cypermethrin and deltamethrin could be determinated were found in previously published works. These conditions were reproduced. Substances were studied in methanol and dimethylformamide solutions. The optimal conditions for determination of these two substances were not found. Voltammetric behaviour of difenzoquat was studied in different pH using Britton-Robinson buffer. The optimal pH 11 was chosen. The reproducibility of measurement was studied at concentration 1·10-4 mol·l-1 , peak was stable (RSD = 3%). Sharp maxima were found at high concentrations of analyte, addition of gelatine led to one well- defined peak. Peak potencial was - 1,4 V. Calibration dependences were measured at concentrations 2·10-7 mol·l-1 - 1·10-4 mol·l-1 . Limit of determination was 6,1·10-7 mol·l-1 . Linear dynamic range of this method was found between concentrations 6,1·10-7 - 2·10-5 mol·l-1 . Difenzoquat was determined in model samples of drinking and river water. Limits of detemination were achieved at concentrations 3,4·10-7 mol·l-1 in drinking water and...
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Electrochemical determination of carboxine using carbon paste electrode
Jarošová, Romana ; Dejmková, Hana (advisor) ; Vyskočil, Vlastimil (referee)
Pesticides are substances widely used for preventing damage by weeds, insects and fungi on plants, feedstuffs, foodstuffs, etc. Those compounds were often overused and this resulted in widespread contamination of the environment. Water ecosystem is the most endangered one - pesticides possess a huge risk for living organisms and primary sources of drinking water. Therefore, development of new analytical methods utilizable for reliable monitoring of these substances in environment is of necessity. Main objective of this diploma thesis was finding the optimal conditions for determination of carboxin using differential pulse voltammetry (DPV), high-performance liquid chromatography with spectrophotometric (HPLC-UV) and electrochemical (HPLC-ED) detection, latter using carbon paste electrode (CPE) as working electrode, reaching the lowest possible limits of detection (LD). Next objective was the application of the developed methods for the determination of carboxin in the sample matrix of river and drinking water. And since the recent trend in development of new analytical methods is their portability (usage in situ), application of miniaturized carbon paste electrode (mCPE) was investigated. Optimal conditions for voltammetric determination using CPE and mCPE were: mixture of Britton-Robinson buffer...
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The use of carbon-based electrodes for the development of new electrochemical methods for the determination of aminonitrophenols
Dejmková, Hana
4 ABSTRACT Methods for the determination of five isomers of aminonitrophenol were developed, based on the technique of differential pulse voltammetry (DPV) and HPLC with amperometric detection. As the working electrodes, boron-doped diamond film electrode (BDDFE) and glassy carvon paste electrode (GCPE) were employed. Preliminary electrode testing was performed by cyclic voltammetry. The methods were aimed to the determination of all five aminonitrophenol isomers in hair dyes and to the determination of 2-amino-4- nitrophenol and 4-amino-2-nitrophenol in body fluids after solid phase extraction. From the voltammetric methods, the one using BDDFE for the cathodic determination in hair dyes exhibits sufficient selectivity. The performance of chromatographic methods was found suitable for the determination of aminonitrophenols in both observed matrices. The applicability of the developed methods was successfully confirmed by the determination of tested analyted in real samples of hair dyes and spiked samples of urine. Preceding measurements are described, dealing with the determination of other oxidizable compounds, containing phenolic or aniline moieties on BDDFE. The obtained results confirm that in some cases, BDDFE shows more resistance to fouling than other carbon-based electrodes, but in most cases, the...
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E x p l o r i n g t h e p o s s i b i l i t y o f u s i n g c a r b o n c o m p o s i t e e l e c t r o d e a s a d i s p o s a b l e s e n s o r f o r d e t e r m i n a t i o n o f p e s t i c i d e s
Bavol, Dmytro ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
In this master's thesis electrochemical determination of cymoxanil and famoxadone was performed on different types of electrodes. The work was focused on finding out optimal conditions for determination of these analytes in aqueous environments by differential pulse voltammetry (DPV) using a composite fiber rod electrode (CFRE), a glassy carbon electrode (GCE) and a capillary carbon paste electrode (CPE). Cymoxanil/famoxadone shows in aqueous environment BR buffer - methanol (9:1) single peak, whose position and height depends on the pH. As pH optimum for CFRE in the cathodic potential range for cymoxanil, pH 4 was chosen, the GCE was chosen pH 7 in the anodic area for famoxadone monitored by the GCE was chosen pH 4, pH 2 was chosen for the CPE. Under the optimal conditions, repeatability in oxidation and reduction area was verified. The optimum conditions of cymoxanil determination on CFRE and famoxadone determination on CPE were utilized for the measurement of the calibration curves. The second set of calibration curves was measured with addition of cymoxanil/famoxadone. Newly developed voltammetric methods were used for the determination of cymoxanil and famoxadone in samples of river water and soil.
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Large-Surface Carbon Film Electrode - A Novel Sensor for Voltammetric Determination of Electrochemically Oxidizable Organic Compounds
Šmejkalová, Hana ; Vyskočil, Vlastimil (advisor) ; Dejmková, Hana (referee)
of the Diploma Thesis In this Diploma Thesis, the electrochemical behavior of 4-nitrophenol (4-NP) was studied at a newly prepared large-surface carbon film electrode (ls-CFE) using techniques of DC voltammetry (DCV) and differential pulse voltammetry (DPV) with the aim to develop sensitive analytical methods for its determination. Voltammetric behavior of 4-NP was investigated in the region of anodic potentials, in dependence on the pH of the medium used (realized using Britton-Robinson buffer). The optimum pH values for the determination of 4-NP were chosen as follows: pH 3.0 (for DCV) and pH 7.0 (for DPV). During anodic oxidation of 4-NP on the ls-CFE at the concentration of the analyte of 1·10-4 mol/l, the passivation of the electrode surface occurred. Thus, it was decided to record series of measurements always at a new carbon film. Using the sample of 4-NP (at the concentration of 1·10-4 mol/l), the repeatability of the application of individual carbon films was tested, with obtained RSD values of 3.7% and 3.6% for DCV and DPV, respectively. Under optimum conditions, the calibration dependences of 4-NP were measured in the concentration range from 1·10-6 to 1·10-4 mol/l, with the limits of quantification (LQs) of 1.5·10-6 mol/l (for DCV at the ls-CFE) and 4.6·10-7 mol/l (for DPV at the...
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Determination of metronidazole on modified carbon paste electrode
Axmannová, Hana ; Dejmková, Hana (advisor) ; Navrátil, Tomáš (referee)
This bachelor thesis examines the possibilities of suppression of the oxygen signal of carbon paste electrode by modification of the electrode with a reductant. Two modifiers were chosen: sodium sulphite and sodium hypophosphite. The unmodified carbon paste electrode was used for the comparison. The possibilities of using these developed electrodes were verified via determination of metronidazole by the differential pulse voltammetry. The conditions for the determination of metronidazole were optimized; for unmodified carbon paste electrode (CPE) buffer of pH 10 was selected as the optimum medium, for carbon paste electrode modified with sodium sulphite (S-CPE) buffer of pH 7 was selected, and finally for carbon paste electrode modified with sodium hypophosphite (F-CPE) buffer of pH 4 was selected as the optimum medium. In this media, concentration dependences were measured and detection and quantification limits were obtained. The possibility of increase of the sensitivity of determination by the accumulation step was studied, but the accumulation of metronidazole was not observed after 5 minutes. The detection and quantification limits for CPE were 1,7×10-5 mol/l and 5,6×10-5 mol/l, for S-CPE 6,8×10-5 mol/l and 2,3×10-4 mol/l and finally for F-CPE 1,3×10-5 mol/l and 4,3×10-5 mol/l. The developed...
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Optimization of electrochemical determination of aminoderovatives of polycyclic aromatic hydrocarbons using chemometric methods
Krejčová, Markéta ; Dejmková, Hana (advisor) ; Schwarzová, Karolina (referee)
In this work, separation conditions of aminoderivatives of polycyclic aromatic hydrocarbons (APAH) mixture were optimized by high performance liquid chromatography with amperometric detection. For the purpose of comparison, the spectrophotometric detector was connected in series with the electrochemical detector. Three-electrode system in the wall-jet arrangement with carbon paste working electrode was chosen for amperometric determination. For the purpose of the optimization, design of experiment was employed, specifically Box-Behnken Design which uses three levels of values of each parameter. Studied parameters were pH of acetate-phosphate buffer, initial percentage of the methanol in mobile phase and its gradient. Derringer's desirability function was applied to evaluate the compromise between the analysis time and the resolution of neighbouring peaks. Using the amperometric detection, ten times lower limits of detection were achieved in comparison with spectrophotometric detection. After preconcentration of the mixture of analytes in the river water by the solid phase extraction, the lowest limit of detection was gained for 2-aminobiphenyl (2·10−10 g ml−1 ) and the highest for 2-aminofluorene (1·10−9 g ml−1 ).
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Investigation of electrochemical properties of carbon fiber rod electrode
Bavol, Dmytro ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
Properties of carbon fiber rod electrode (CFRE) were studied in this bachelor thesis. The potential window width in various basic electrolytes such as NaOH, KCl, and HClO4 was measured. Cyclic voltammetry (CV) was employed to investigate the course of the electrode reaction as well as the influence of the size and modification of the electrode surface on the results of the measurement of a model redox system ferrocyanide/ferricyanide. The CFRE applicability was verified by the determination of pesticide 2,6-dichloro-4-nitroaniline (dichloran) using DC voltammetry (DCV) and differential pulse voltammetry (DPV). In the presence of BR buffer- methanol (9:1), dichloran provides one or two redox waves, whose position and height depend on the pH. pH 10 was selected as optimum for all further measurements. Hence, the reproducibility dependency was found in this medium.
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Voltammetric determination of anilazine on silver solid amalgam electrode
Bystrianský, Martin ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
Anilazine (4,6-dichloro-N-(2-chlorophenyl)-1,3,5-triazin-2-amine) is a fungicide from a group of triazine pesticides. These have been very widely used but for their toxicity for water environment they are being cancelled. Use of anilazine is not allowed anymore in the European Union. However, traces of its residues are able to find in environmental samples. The diploma thesis deals with determination of anilazine using silver solid amalgam electrode modified by mercury meniscus (m-AgSAE). Differential pulse voltammetry was used. For the determination, an acidic solution is necessary. In the work Britton-Roninson buffer pH = 2 was used. This is because of electrochemical reduction of anilazine (and other triazines) which is started by protonization of heterocycle ring. Anilazine exhibits one single well-defined peak, the potential of the peak was about Ep = -827 mV (vs. 3 mol l-1 argentochloride electrode). The limit of quantification achieved in surface water was 2 µmol.l-1. Other two possibilities of getting lower limit of quantification were examined - Adsorptive Stripping Voltammetry (AdSV) and preconcentration by Solid Phase Extraction (SPE). Using AdSV the limit of quantification LQ = 0,5 µmol.l-1. Conditions of adsorption were as following: Eacc = -100 mV, tacc = 60 s. For SPE, 200-mg columns...
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