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Voltammetric Determination of Tumor Biomarkers using Flow Injection Analysis with Amperometric Detection
Makrlíková, Anna ; Matysik, F.-M. ; Barek, J. ; Vyskočil, V.
Three tumor biomarkers (homovanillic acid, vanillylmandelic acid,\nand 5-hydroxyindole-3-acetic acid) have been determined by flow\ninjection analysis with amperometric detection at screen-printed\ncarbon electrodes in optimum medium of Britton-Robinson buffer\n(0.04 mol l-1, pH = 2.0). Dependences of the peaks current on the\nconcentration of biomarkers were linear in the tested concentration\nregion from 0.05 to 100 mu mol l-1, with the limits of detection of\n0.065 mu mol l-1 for homovanillic acid, 0.053 mu mol l-1 for vanillylmandelic\nacid, and 0.033 mu mol l-1 for 5-hydroxyindole-3-acetic acid (calculated\nfrom heights), and 0.024 mu mol 1-1 for homovanillic acid,\n0.020 mu mol l-1 forvanillylmandelic acid, and 0.012 mu mol l-1 for 5-hydroxyindole-3-acetic acid (calculated from areas), respectively.
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Pilot Experiments With a Micro-Volume Voltammetric Cell for the Determination of Electrochemically Reducible Organic Compounds
Skalová, Štěpánka ; Barek, J. ; Rodrigues, J. A. ; Goncalves, L.M. ; Navrátil, Tomáš ; Vyskočil, V.
A new micro-volume voltammetric cell for analysis of small volumes\nof electrochemically reducible organic compounds was developed\nand tested. The sample (20-100 mu L) is placed in a narrow glass tube\nwith an agar membrane at the bottom and the working electrode is\nimmersed into the sample. The agar membrane, as anion permeable\nlayer, electrically connects the workin g e lectrode immersed in the\nanalysed sample in the glass tube with a large-volume compartment\n(20 mL) filled with Britton-Robinson buffer, where conventional nonminiaturized\nreference and auxiliary electrodes are placed. The system\nwas tested using a polished silver solid amalgam electrode\n(p-AgSAE) as a working electrode. Sodium anthraquinone-2-sulfonate\nwas used as a model compound because it is intended to use this\nsystem to monitor electrochemically reducible organic compounds.
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Marketing communication of travel agencies on the social media environment
Barek, Jan ; Gála, Libor (advisor) ; Molnár, Zdeněk (referee)
The following master thesis is focused on the issue of marketing communication of travel agencies on the social media environment. It maps the current involvement of five selected social media to the promotion of the seven most important travel agencies in the Czech Republic. The author compares the real state of communication to social media with his own exploration of travel agent preferences. The comparison is based on a series of recommendations for the marketing communication of travel agencies on social media at the end of the work.
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Voltammetric Determination of Diafenthiurone Using Carbon Paste Electrode
Markvart, Jan ; Barek, Jiří (advisor) ; Zima, Jiří (referee)
In this bachelor thesis voltammetric behavior of Diafenthiuron using carbon paste electrode was investigated. Methodes used in this thesis were differential pulse voltammetry, cyclic voltammetry and DC voltammetry. Britton-Robinson buffer of optimal pH in mixture with methanol was used as a base electrolyte. Optimal pH of Britton-Robinson buffer was pH 3 for DC voltammetry and cyclic voltammetry and pH 5 for differential pulse voltammetry. Under optimal conditions limit of detection and limit of quantification for differential pulse voltammetry and DC voltammetry in 50% methanol were estimated. For differential pulse voltammetry detection limit was found to be 1,5* 10-5 mol/l and quantification limit was found to be 5* 10-5 mol/l. For DC voltammetry the detection limit was 1,7* 10-5 mol/l and quantification limit was 5,8* 10-5 mol/l.
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Voltammetric Determination of Selected Nitrated Heterocyclic Compounds Using Various Amalgam-Based Electrodes
Fischerová, Dana ; Barek, Jiří (advisor) ; Vytřas, Karel (referee) ; Navrátil, Tomáš (referee)
Development and testing of new non-toxic electrode materials, their preparation and the development of analytical methods applicable for determination of selected substituted nitrobenzimidazoles is the main aim of this Ph.D. Thesis. New working electrodes based on the modification of surface of polished silver solid amalgam electrode (p-AgSAE) by other electrodes materials which contain mainly mercury (mercury meniscus modified silver solid amalgam electrode (m-AgSAE), mercury film modified silver solid amalgam electrode (MF-AgSAE)), bismuth (bismuth film on silver solid amalgam electrode (BiF-AgSAE)) or carbon (electrode modified by microcrystalline natural graphite-polystyrene composite transducer (CFE)) were developed. The optimum deposition time for preparation of film electrodes were discover and verified. Their electrochemical behavior (stable and reproducible responses during measurement) were investigated and further used in voltammetric determination of mutagenic or carcinogenic environmental pollutants 2-amino-6-nitrobenzimidazole (ANBT) and 5-nitro- benzimidazole (5-NBIA). These analytes could be determined by direct current voltammetry (DCV) or differential pulse voltammetry (DPV). The attempt at increasing the sensitivity using adsorptive striping DCV or DPV at all tested electrodes...
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Electrochemical Determination of Fomesafen
Maška, Jan ; Barek, Jiří (advisor) ; Fischer, Jan (referee)
The submitted work deals with the application of voltammetric determination of Fomesafen using non-traditional mercury meniscus modified silver solid amalgam electrode on model samples of Fomesafen in real aqueous matrices of drinking and river water. This method of measurement has been developed and optimized in my bachelor thesis, which the diploma thesis is related to. Fomesafen belongs to a group of herbicides used on a mass scale in the late 20th century in the USA and in many countries around the world still used even today. Among its side effects according to the EPA include, among others, potential carcinogenicity to humans and confirmed carcinogenicity to some mammals (such as rats) which led to a legislative regulation on its use in many countries around the world including the USA, the European Union and many others. Silver solid amalgam electrode has been developed with the intention to limit the use of mercury in accordance with new legislation of the European Union and the concept of green analytical chemistry. Despite the low levels of mercury mainly bound in the form of virtually harmless silver amalgam electrode retains very similar electrochemical properties with proven mercury electrodes. As part of the thesis, direct determination of a number of partial extraction of Fomesafen...
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Silver Amalgam Electrodes in Electroanalysis of Selected Agrochemicals
Daňhel, Aleš ; Barek, Jiří (advisor) ; Vytřas, Karel (referee) ; Ludvík, Jiří (referee)
4 ABSTRACT Development and testing of novel non-toxic electrode materials, detection arrangements and analytical methods applicable in determination of selected agrochemicals is the main aim of this Ph.D. Thesis. New working electrodes based on silver solid amalgam paste (AgSA-PE) with organic pasting liquid and other based on crystallic silver amalgam (CAgAE) were developed, their electrochemical behaviour investigated and further used in voltammetric determination of widespread and toxic environmental pollutant 4-nitrophenol (4-NP). This analyte could be determined by DPV at AgSA-PE with limit of detection (LD) 1×10í6 mol lí1 and using CAgAE with LD 4×10í7 mol lí1 , both in 0.2 mol lí1 acetate buffer pH 4.8. Attempts to decrease LDs by utilization of adsorptive stripping voltammetry were not successful in either case. Crystallic silver amalgam was also successfully used for construction of microcylindric flow-through cell and tested for amperometric determination of nitrophenol mixture in HPLC-ED system. Both novel electrodes were found to be suitable alternatives to toxic mercury electrodes and the CAgAE seems to be promising working electrode for flowing systems. Method for sample preparation and voltammetric determination of broad-spectrum herbicide Glyphosate in contaminated soil samples was also...
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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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