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Determination of cholesterol, 7-dehydrocholesterol and cholecalciferol by HPLC with spectrophotometric and electrochemical detection
Dostálková, Lucie ; Schwarzová, Karolina (advisor) ; Vyskočil, Vlastimil (referee)
The aim of this thesis is to verify the possibility of simultaneous determination of three structurally related biologically active substances (cholesterol, 7-dehydrocholesterol and cholecalciferol) after previous separation by high-performance liquid chromatography followed by electrochemical (on a boron-doped diamond electrode) and spectrophotometric detection, which were compared in this work. The influence of the water content in the mobile phase (in the range of 0-10 %) on the retention factor of the analytes and their response for both types of detectors was investigated. Using all mentioted water contents, the analytes baseline-separated. As the water content increased, the retention factor of the analytes increased as well as the background current for higher positive detection potentials. Based on the recorded hydrodynamic voltammograms, the optimum detection potential + 1.8 V was chosen. The optimum wavelength for spectrophotometric detection was 200 nm. The concentration dependence was measured in an of 50 mmol l−1 sodium perchlorate in acetonitrile mixed with water (95:5, v/v). The spectrophotometric detector provided lower detection limits compared with the electrochemical detector, which had detection limits of 2.3 μmol l−1 for cholesterol, 1.4 μmol l−1 for 7-dehydrocholesterol and...
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Utilization of complexation of tebuconazole with Cu(II) ions for its voltammetric detection
Dostálková, Lucie ; Fischer, Jan (advisor) ; Křížek, Tomáš (referee)
Tebuconazole is a triazole fungicide used in agriculture that can be present in the environment and have a negative effect on various organisms. Therefore, the electrochemical properties of tebuconazole and its complexation with Cu(II) ions on a boron doped diamond electrode were studied for its possible indirect detection in the presence of these ions. For the determination of Cu(II) ions, conditions in the concentration range 0.1-10 mol l-1 were optimized by differential pulse voltammetry in a 0.01 mol l-1 HNO3 environment on anodically oxidized BDDE, the limit of quantitation was 0.087 µmol l-1 . After optimization of the conditions, the indirect determination of tebuconazole was tested. The signal of free Cu(II) ions after the addition of tebuconazole was monitored. A decrease in this signal was observed and a linear calibration dependence could be measured for a decrease in the signal of 10 µmol l-1 Cu(NO3)2 in the concentration range of 2-10 µmol l-1 tebuconazole and for 1 µmol l-1 Cu(NO3)2 in the concentration range of 2-10 µmol l-1 and 10-100 µmol l-1 tebuconazole. Complexation of tebuconazole with Cu2+ was shown to occur almost instantaneously. Tebuconazole itself gives an anodic peak at a potential of +1550 mV in aqueous medium of 0.01 mol l-1 HNO3. Using differential pulse voltammetry,...
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