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ELECTROCHEMICAL DETECTOR WITH ELECTRODES ARRAY AND ROTATING DISK
SAJDLOVÁ, Zuzana
The thesis deals with the testing and optimization of hydrodynamic conditions of the electrochemical detector, which consists of a flow cell containing the electrochemical sensor with an array of electrodes. The flow cell includes a rotating disc-shaped component, which allows radial flow of analytes along the sensor electrodes. This principle imitates the rotating disk electrode, with the difference that here the electrodes are immobile. Hydrodynamic phenomena in this case are similar to RDE. Therefore, the theoretical part of my work deals with hydrodynamics and mass transfer for the well-described case of rotating disk electrode. It was found that in the current set-up under certain conditions, an analyte flowed back from the output cell channel to the sensor, even at the laminar flow. This causes a nonlinear response of the electrodes and their low reproducibility. The solution is to reduce the distance between the rotation component and the electrodes surface and reduce flow speed of analyzed liquid towards the sensor. A novel type of sensor with annular electrodes was designed and tested. It showed four times higher conversion rate of the analyte compared with the originally used AC9 electrochemical sensor having electrodes in the form of full circles lying on a circumference of a common circle. Based on calculations, conversion of the analyte on the plane electrode can be increased up to 100% when using this annular sensor, adjusting flow cell and reducing of the input flow rate. The detector was connected to the liquid chromatograph and its function was tested on two substances - ascorbic acid and dopamine. For the current detector these parameters were set: dynamic range, linearity, noise, detection limit, time constant and the temperature range at which the detector can be operated.
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The content of ascorbic acid in fruits of selected species of tomatoes
VOSPĚLOVÁ, Renata
The goal of this dissertation was to determine and to compare the content of the ascorbic acid in the fruitages of the selected mutations of the tomatoes. There was established a small site grower focus in the own garden, for which were selected three mutations of the tomatoes plants (Diana, Oranže, Dulcia). There was determined the content of the ascorbic acid by the titrating Method with 2,6-dichlorphenolindophenole in the fruitages of the tomatoes after the harvest. Further on there was determined the content of the ascorbic acid with the same method by the tomatoes, which were bought in the common shopping chains in the Czech republic.
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