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Voltammetric Determination of 4-Nitrobiphenyl at a Mercury Meniscus Modified Silver Solid Amalgam Electrode
Horáková, Eva ; Schwarzová, Karolina (referee) ; Barek, Jiří (advisor)
The presented bachelor thesis is devoted to study of electrochemical behavior of 4-nitrobiphenyl (4-NBP) and to finding of optimum conditions for its' determination using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE). The aim was to achieve the lowest possible limit of determination and to verify the applicability of the newly developed method for determination of 4-NBP in model samples of drinking water. Methanol-acetate buffer pH 4,8 (3:7) was found as an optimum medium for the determination of 4 NBP at a m-AgSAE in deionized water. During DCV it is not necessary to apply electrochemical regeneration of the working electrode, during DPV it is proper to apply following regeneration potentials: Ereg,1 = 0 mV, Ereg,2 = -1300 mV. The concentration dependence of the peak current was found to be linear for both methods for 10-5, 10-6 and 10-7 mol∙l-1 concentration ranges. The limit of determination of 4-NBP both by DCV and by DPV is 2∙10-7 mol∙l-1. The optimum medium for the determination of 4-NBP in drinking water is the mixture of the sample and acetate buffer pH 4,8 in the 9:1 ratio.. During DCV regeneration was not applied, during DPV it was applied with the following regeneration potentials: Ereg,1...
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Voltammetric Determination of Metronidazol at a Polished Silver Solid Amalgam Composite Electrode
Škvorová, Lucie ; Zima, Jiří (referee) ; Barek, Jiří (advisor)
The aim of this work was to find out the optimal conditions for voltammetric determination of metronidazole, which is used as an anti-tumor drug. The stability of stock solution of metronidazole in deionized water was monitored using UV-VIS absorption spectrophotometry. Optimum conditions for voltammetric determination of metronidazole at a polished silver solid amalgam composite electrode (p-AgSA-CE) have been investigated. The dependence of voltammetric behavior of metronidazole (1∙10-4 mol/L) on pH of analyzed solution has been investigated using DC voltammetry (DCV) and differential pulse voltammetry (DPV) in the pH range 2,1 - 12,1 in aqueous media of Britton- Robinson (BR) buffer. For electrochemically reducible nitro group of metronidazole, the mechanism of voltammetric reduction at p-AgSA-CE was proposed. The optimum medium of aqueous BR buffer pH 4.0 was chosen for measuring the concentration dependences for both voltammetric techniques. The concentration range 2∙10-6 - 1∙10-4 mol/L of metronidazole was measured using DCV and DPV at p-AgSA-CE with reached limits of quantification (LQs) 2∙10-6 mol/L and 4∙10-6 mol/L for DCV and DPV, respectively. For comparison of used voltammetric techniques with supplemental analytical method, the concentration range 2∙10-6 - 1∙10-4 mol/L of metronidazole...
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Voltammetric Determination of 4-Aminobiphenyl at Modified Carbon Paste Electrodes
Kalusová, Michaela ; Barek, Jiří (advisor) ; Navrátil, Tomáš (referee)
Amino derivatives of polycyclic aromatic hydrocarbons are well-known chemical carcinogens which should be carefully monitored in our environment. They are amenable to anodic oxida- tion on suitable solid or paste electrodes. This fact was exploited for voltammetric determina- tion of 4-aminobiphenyl on unmodified carbon paste electrode and carbon paste electrodes modified by montmorillonite and sepiolite. The optimum pH of BR buffer for measurement on unmodified carbon paste electrode is pH 2, pH 10 for CPE-SEP and pH 11 for CPE-MMT. It was possible to increase sensitivity of the determination using adsorptive stripping voltam- metry on modified electrodes. The optimum time for accumulation of 4-aminobiphenyl is 5 minutes. The limits of quantification of the order of 10−6 mol dm−3 were obtained for each electrode. After accumulation, the limits of quantification decreased to the 10−7 mol dm−3 . The newly developed method was tested for the determination of 4-aminobiphenyl in model sam- ples of drinking and river water, reaching limits of quantification of the order of 10−7 mol dm−3 .
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Determination of double bond position in higher hydrocarbons
Jersáková, Jana ; Barek, Jiří (advisor) ; Valterová, Irena (referee)
Hydrocarbons including alkenes are in addition to wax esteres, alcohols, ketones and acids one of the main compounds of insect cuticle. Hydrocarbons protect insect body against dry, water and UV radiation. In some species they play an important role in mutual communicative and recognition. Hydrocarbons profile can in some cases serve as fingerprint defining species specificity. Therefore, the position of double bonds in cuticular hydrocarbons is important. This work describes utilization of catalytic hydroxylation with polymer-supported osmium tetroxide as a derivatization technique to determine double bond position. Reaction conditions of hydroxylation and mass spectrometric fragmentation of derivatized alkenes were optimized for standard containing one double bond. These conditions were applied to real samples from the american cockroach Periplaneta americana and blowfly Neobellieria bullata.
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Determination of Selected Nitrophenols Using Modified Carbon Paste Electrodes
Hranická, Zuzana ; Barek, Jiří (advisor) ; Zima, Jiří (referee)
The voltammetric behavior of selected nitrophenols (2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol) was investigated by differential pulse voltammetry (DPV) and by adsorptive stripping voltammetry (AdSV) at an unmodified electrode (CPE) and a clay-modified carbon paste electrodes modified by montmorillonite (MMT-CPE) and sepiolite (SEP-CPE) using electrochemical reduction and oxidation in Britton-Robinson buffer. For reduction, optimum conditions have been found at pH 2 for 2-NP and 4-NP, at pH 3 for 2,4-DNP and at pH 4 for 2,4,6-TNP. For oxidation, optimum conditions have been found at pH 2 for 2-NP and 4-NP and at pH 5 for 2,4-DNP. Voltammetric determination using electrochemical oxidation is not a suitable method for 2,4,6-TNP. The lowest detection limits were obtained for 2-NP using cathodic AdSV on SEP-CPE with 2,9·10-7 mol.dm-3 , for 4-NP using cathodic DPV on MMT-CPE with 2·10-6 mol.dm-3 , for 2,4-DNP using cathodic AdSV on SEP-CPE with 2,7·10-7 mol.dm-3 and for 2,4,6-TNP using cathodic DPV on unmodified electrode with 4,8·10-7 mol.dm-3 . Determination of mixture 2-NP and 4-NP and the possibility of the selective determination using open circuit sorption with DPV detection was further studied.
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