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Voltammetric Determination of Selected Nitroaromatic Explosives
Křížová, Tereza ; Vyskočil, Vlastimil (advisor) ; Fischer, Jan (referee)
This Diploma Thesis is focused on study of electrochemical behavior of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (picric acid) on finding the optimum conditions for their determination using direct current voltammetry (DCV) and differential pulse voltammetry (DPV) at a mercury meniscus modified silver solid amalgam electrode (m-AgSAE) in the solution of Britton-Robinson (BR) and on finding of the limit of quantification (LQ) for these substances. Practical applicability of the newly developed methods was verified on direct determination of TNT and picric acid in model samples of drinking and river water. Moreover, the electrochemical behaviors of TNT and picric acid was studied using cyclic voltammetry (CV). Optimum medium for the determination of TNT at m-AgSAE was: methanol-BR buffer pH 4.0 (1:9). Upon the DCV it is proper to apply regeneration potentials Ereg,1= 0 mV and Ereg,2= -1100 mV and upon the DPV was apply regeneration potentials Ereg,1= 0 mV and Ereg,2= -600 mV were applied. The concentration dependence of the peak current was found to be linear for both techniques over the concentration range of 1·10-6 -1·10-4 mol/l with LQ of 0.54 µmol/l (for DCV) and 0.46 µmol/l (for DPV). The method developed for the determination of TNT were verified on the model samples of drinking...
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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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Voltammetric determination of diazepam and nordiazepam on meniscus modified silver solid amalgam electrode
Samiec, Petr ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
Voltammetric methods for the determination of diazepam (DZ) and nordiazepam (NDZ) were developed. Techniques differential pulse voltammetry (DPV) and DC voltammetry for determination of both substances at meniscus modified silver solid amalgam electrode (m-AgSAE) were used. Effect of pHa in media of mixture of Britton-Robinson buffer and methanol (9:1) and 0,1 mol.l-1 NaOH was studied. Stability of the signal with repeated measurements in 0,1 mol.l-1 and methanol (9:1) was monitored. Optimal pHa 13,2 of 0,1 mol.l-1 NaOH was used for determination of DZ by DPV and DCV techniques. Optimal pHa 10,2 in media of mixture of Britton-Robinson buffer and methanol (9:1) was used for determination of NDZ by DPV and DCV techniques. Under these conditions were measured linear dependences in the calibration. Concentration range of DZ was measured with DCV in range of 1.10-4 - 6.10-6 mol.l-1 and DPV with DCV technique in range of 1.10-4 - 2.10-6 mol.l-1. Concentration range of NDZ was measured with DCV technique in range of 1.10-4 - 4.10-6 mol.l-1 and DPV technique in range of 1.10-4 - 2.10-6 mol.l-1. The limit of detection was calculated for DZ 6,6 .10-6 mol.l-1 with DCV and 1.10-6 mol.l-1 with DPV. The limit of detection was calculated for NDZ 5,5.10-6 mol.l-1 with DCV and 1,7.10-6 mol.l-1 with DPV. Developed method...
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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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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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Voltammetric Determination of Genotoxic 6-Nitrochrysene at a Mercury Meniscus Modified Silver Solid Amalgam Electrode
Šmídková, Monika ; Vyskočil, Vlastimil (advisor) ; Fischer, Jan (referee)
This Bachelor Thesis is devoted to the study of electrochemical behavior of 6-nitrochrysene (6-NCH) and to the finding of the 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). For measuring the concentration dependences of 6-NCH, the optimum medium methanol - BR buffer pH 9.0 (1:1) and the proper regeneration potentials Ereg,1 = 0 mV, Ereg,2 = -600 mV have been chosen for DCV at m-AgSAE and the medium methanol - BR buffer pH 10.0 (1:1) and the proper regeneration potentials Ereg,1 = 0 mV, Ereg,2 = -750 mV have been chosen for DPV at m-AgSAE. The concentration dependence was found to be linear only for the lowest concentration range of 10-7 mol·l-1 . In the concentration range of 10-6 mol·l-1 , the concentration dependences observed were polynomial. This result indicates a possible adsorption of 6-NCH on the surface of working electrode. Reached limits of quantification (LQ) were 1·10-7 mol·l-1 for DCV at m-AgSAE and 5·10-8 mol·l-1 for DPV at m-AgSAE. For comparison, the concentration dependence of 6-NCH was measured in methanol using UV-VIS spectrophotometry. Reached LQ ~ 1·10-7 mol·l-1 is comparable with LQs reached using DCV and DPV techniques.
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Voltammetric determination of drugs doxycycline and dimenhydrinate using carbon film electrode
Humpolíková, Jiřina ; Fischer, Jan (advisor) ; Dejmková, Hana (referee)
This bachelor's thesis concerns the determination of doxycycline (DX) and dimenhydrinate (DMH) by the methods DC voltammetry (DCV) and differential pulse voltammetry (DPV) on a carbon film electrode (CFE). The optimum conditions for voltammetric determination of DX and DMH were found and under these conditions, concentration dependences were measured and the limits of quantification (LOQ) were calculated for each method. The media of BR-buffer pH 12.0 was chosen as optimum for DCV and DPV determination of DX at CFE. For both DCV and DPV, the linear concentration dependences were obtained in concentration ranges of DX from 20 µmol·l-1 to 100 µmol·l-1 with LOQ 15,4 µmol·l-1 for DCV and 15,2 µmol·l-1 for DPV. DX was determined in drug using DCV under optimized conditions and for comparison of used voltammetric method DX in drug was determined also using UV-VIS spectrophotometry with consistent results. The optimum medium of BR buffer pH 3.0 was chosen for determination of DMH by DCV and pH 2.0 for DPV. The calibration range 2,0 - 10,0 µmol·l-1 of DMH was received using DCV and 0,2 - 1,0 µmol·l-1 of DMH was recevied using DPV at CFE with reached LOQ 0,08 µmol·l-1 for DCV and 0,02 µmol·l-1 for DPV. DMH was determined in comertional drugs using DCV on founded conditions. The stability of stock solution...
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Polarographic and Voltammetric Determination of Fomesafen
Maška, Jan ; Barek, Jiří (advisor) ; Fischer, Jan (referee)
The work is related to the polarographic and voltammetric determination of Fomesafen on the basis of its cathodic reduction using classical dropping mercury electrode (DME), hanging mercury drop electrode (HMDE) and non-traditional mercury meniscus modified silver solid amalgam electrode (m-AgSAE). Silver solid electrode (AgSAE) was developed as an alternative to mercury electrodes regarding legislative complications limitating usage of mercury because of its supposed toxicity. Properties of this electrode are very similar to the ones of mercury electrodes, mainly outstandingly broad cathodic potential region but excelent sensitivity either. As an electrode material, silver amalgam was used which non-toxicity is obvious given for example even by its long-term usage in stomatology as a main item for production of tooth-fillings. For model determination, Fomesafen was chosen because of its previous and sometimes also present usage as a major component of herbicid agents in agriculture. Its factual toxicity was actually proven and it was also classified as a potential carcinogen for humans. Historically, its usage was relatively deliberately massive, significant was e.g. in USA, but presently it was already forbidden in many countries. The intention of the work was to compare the analytical qualities...
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Voltammetric Determination of Chloramphenicol and Ofloxacin at Boron Doped Diamond Film Electrodes
Ječmínková, Jana ; Fischer, Jan (advisor) ; Vyskočil, Vlastimil (referee)
Voltammetric methods for the determination amphenicol antibiotic chloramphenicol (CAP) and quinolone antibiotic Ofloxacin (OFL) were developed. TTechniques differential pulse voltammetry (DPV) and DC voltammetry (DCV) for determination of both substances at boron doped diamond film electrode (BDDFE) were used. The effect of pH of Britton-Robinson buffer was tested and the stability of the signal with repeated measurements was monitored. Optimal pH 6 was used for determining of CAP by both, DPV and DCV techniques. Media of pH 4 for determining of OFL by DPV and DCV was optimal. Under these conditions linear dependences in the calibration concentration region 1.10 -6 - 1.10-4 mol.l -1 were obtained. The limit of determination for the method for CAP by DPV at 3.10 mol.l , by -6 -1 DCV at 3.10 mol.l and for -6 -1 OFL by DPV at 1.10 mol.l -6 -1 and by DCV at 4.10 mol.l -7 -1 was found. The developed methods were used for the determination of CAP in the drug samples Spersadex comp. and OFL determination in drug samples Zanocin 200. Method for solid phase extraction of OFL from samples of urine with voltammetric detection was developed with limit of determination at 7.10 mol.l . -6 -1
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