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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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Voltammetric Determination of Dinitronaphthalenes Using Single Crystal Silver Amalgam Electrode
Tvrdíková, Jana ; Barek, Jiří (advisor) ; Dejmková, Hana (referee)
Voltammetric methods for determination of 1,3-dinitronaphthalene (1,3-DNN), 1,5-dinitronaphthalene (1,5-DNN) and 1,8-dinitronaphthalene (1,8-DNN) using DC voltammetry (DCV) and differential pulse voltammetry (DPV) at novel single crystal silver amalgam electrode (CAgAE) were developed in this work. Developed methods may be used for determination of 1,3-DNN within a concentration range 2 - 10 μmol.L-1 with LoQ 2 μmol.L-1 using DCV and 1 - 100 μmol.L-1 with LoQ 1 μmol.L-1 by DPV; 1,5-DNN wihin a concentration range 2 - 10 μmol.L-1 with LoQ 2 μmol.L-1 using DCV and 1 - 10 μmol.L-1 with LoQ 1 μmol.L-1 by DPV and 1,8-DNN within a concentration range 2 - 10 μmol.L-1 with LoQ 2 μmol.L-1 using DCV and 0,3 - 1 μmol.L-1 with LoQ 0,3 μmol.L-1 by DPV. An attepmt to decrease LoQ by adsorptive stripping differential pulse voltammetry was not successful. Process of electrochemical reduction of selected dinitronaphthalenes on the working electrode was also studied by cyclic voltammetry. This work verified the use of CAgAE as alternative electrode material to mercury electrodes for determination of electrochemically reducible organic compounds in aqueous-methanolic media. Small dimensions of the CAgAE are the main advantages which predetermine its use in voltammetric microvolume batch analysis and amperometric detection in...
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Determination of amino acids using a coulometric detector with replaceable filling
Prokešová, Edita ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
This Master Thesis evolves the previously developed construction of coulometric detector with replaceable filling with microspheres of glassy carbon, modifies the filling proces and introduces copper microparticles as the electroactive material. In case of carbon microbeads, different composition of the filling suspension and rapid fillig replacement by means of air bubbles injecting is tested; in case of copper microbeads, also the general construction of the detector was modified and besides the filling process, suitable procedure for the activation of the copper surface and for the cleaning of the detector was seeked. Multivariate statistical analysis was used for the development of method for the determiantion of tyrosine using FIA with electrochemical detection on the detector made of glassy carbon beads. The optimum conditions for the determination of tyrosine were: flow rate 0.6 ml·min-1 , the potential of 1.3 V, the volume ot the injection loop of 50 µl, in a B-R buffer pH 4.5. The limit of detection was determined to 0.5 µmol·dm-3 and the limit of quantification to 1.6 µmol·dm-3 . Phenylalanine was determined by the FIA with the coulometric detection, using detector filled with copper microparticles. optimum conditions for the determination were as follows: flow rate 0.6 ml·min-1 phosphate...
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Voltammetric determination of triclosan at carbon paste electrode
Malá, Petra ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
Differential pulse voltammetry was used to study the behaviour of triclosan at a carbon paste electrode. The influence of various pH values of Britton-Robinson buffer and various amounts of methanol was studied. Optimal found value of pH was pH 11 and there was no difference in voltammetric signal in the media with various amounts of added methanol. Accumulation on the electrode surface was negligible and did not result in significant triclosan signal increase. The limit of detection of 1,2·10-7 mol dm-3 and the limit of quantification of 2,0·10-7 mol dm-3 triclosanwere found. Real samples were studied by differential pulse voltammetry, high-performance liquid chromatography and spectrophotometry. The results were compared and applicability of differential pulse voltammetry to real samples without special preparation step was evaluated. Surfactants present in samples obscured the voltammetric determination of triclosan in some samples even in case of the utilization of standard addition method.
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Voltametric Determination of 4-Nitrophenol at a Bismuth Film Electrode
Hausner, Jiří ; Barek, Jiří (advisor) ; Dejmková, Hana (referee)
This Bachelor Thesis is focussed on the study of electrochemical behaviour of 4-nitrophenol (4-NP) and the search for optimal conditions for its voltammetric determination at a bismuth film-modified gold electrode (BiF-AuE). Voltammetric behaviour of 4-NP (c = 1×10-4 mol L-1 ) was investigated using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) in dependence on the pH of the medium used (Britton-Robinson buffers). For both techniques, Britton-Robinson buffer of pH 7.0 was chosen as the optimum medium. Repeatability of the determination of 4-NP (c = 1×10-4 mol L-1 ) was 0.6 % and 0.9 % for DCV and DPV, respectively. Calibration dependences of 4-NP were measured in the concentration range from 1×10-6 to 1×10-4 mol L-1 under the optimum conditions. Attained limits of quantification (LQs) were 7.6×10-7 mol L-1 and 1.5×10-6 mol L-1 for DCV and DPV, respectively. The applicability of the newly developed voltammetric methods for the determination of 4-NP was verified on model samples of drinking water with LQ 7.5×10-6 mol L-1 for DCV at the BiF-AuE and 1.4×10-6 mol L-1 for DPV at the BiF-AuE.
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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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The use of carbon-based electrodes for the development of new electrochemical methods for the determination of aminonitrophenols
Dejmková, Hana ; Zima, Jiří (advisor) ; Ludvík, Jiří (referee) ; Vytřas, Karel (referee)
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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Voltammetric determination of oxidizable derivatives of aromatic hydrocarbons using screen printed electrode
Janovcová, Marcela ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
Development of the cheap, fast and reliable methods for the determination of aminoderivatives of polycyclic aromatic hydrocarbons has great significance not only for analytical chemistry, but mainly for human, because most of these compounds are either suspected or even proven carcinogens. This work deals with the determination of two proven carcinogens 2-aminonaphthalene (2-AN) and 4-aminobiphenyl (4-ABP) using screen printed carbon electrodes (SPCE). Using the methods of cyclic voltammetry (CV) and differential pulse voltammetry (DPV) properties and behavior of these electrodes were investigated. The possibility of the activation with phosphate buffer, pH = 7, was observed and the cleaning of the electrode using electrochemical cycling was demonstrated. Using DPV the detection limit of 2-AN 16 µmol·dm-3 and of 4-ABP 7,3 µmol·dm-3 was reached in B-R buffer pH = 12.
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Application of carbon based electrodes for electrochemical detection in flow system
Mika, Jan ; Dejmková, Hana (advisor) ; Fischer, Jan (referee)
Carbon is due to its electrochemical properties a favourite material for construction of electrodes suitable for detection in flow system. The two most often used techniques (coulometric and amperometric) will be discussed in this Thesis. Carbon paste electrodes (CPE) represent the amperometric detectors. CPE are unstable in the medium with high content of organic solvents, which might complicate their application in HPLC, where the mobile phase contains organic component. It is interesting, that glassy carbon paste electrodes are more stable under such conditions. The change of surface and response of the electrode caused by the effect of methanol are described in this Thesis along with the possible reason of stability of GCPE. Roughing of the surface exposed to methanol is demonstrated by confocal microscopy. This effect leads to increase of height of the peak, background current and noise and to the shift of peak potential to less positive values. These changes are dependent on the time of exposure and the concentration of methanol. Coulometric detectors work with high conversion effectiveness and sensitivity, but in case of their passivation, reactivation is a relatively complicated problem, often leading to the replacement of electrode material. Answer to this problem can be given by using...
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