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Voltammetric detection of 27-hydroxycholesterol on boron-doped diamond electrode
Michnová, Kristýna ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
The aim of this bachelor thesis was to study the voltammetric behavior of 27-hydroxycholesterol using boron-doped diamond electrode. The influence of several factors on the current response of 27-hydroxycholesterol was investigated: the effect of the supporting electrolyte, concentration of perchloric acid, polarization rate, water content, and pH effect. The study was conducted using cyclic voltammetry in a perchloric acid or sodium perchlorate in acetonitrile. 27-hydroxycholesterol provided a current response in the anodic region with a potential around +1450 mV vs. Ag/0.01 mol l-1 AgNO3 in 1 mol l-1 NaClO4 in acetonitrile in the presence of 0.1 mol l−1 perchloric acid in acetonitrile (water content 0.43 %) and 0.1 mol l−1 sodium perchlorate in acetonitrile. Furthermore, concentration dependence was measured using differential pulse voltammetry resulting in a limit of detection (LOD) of 2.71 μmol l−1 and a limit of quantitation (LOQ) of 9.04 μmol l−1 . It was demonstrated that the direct current voltammetry method does not achieve comparable limit values. Key words 27-hydroxycholesterol, boron-doped diamond electrode, oxidation, oxysterols, voltammetry
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Voltammetry and liquid chromatography of cholesterol, its precursors, and oxidation products
Kubešová, Jana ; Schwarzová, Karolina (advisor) ; Baluchová, Simona (referee)
Electrochemical detection of sterols is difficult. This thesis aims to study the voltammetric behaviour of selected oxysterols, i.e. 25-hydroxycholesterol and 7-ketocholesterol on the boron-doped diamond electrode. Further, an HPLC method with spectrophotometric and electrochemical detection was developed for separation of selected sterols. The study was performed using cyclic and differential pulse voltammetry. 0.1 mol l−1 perchloric acid in acetonitrile (water content 0.55 %) was chosen as the most suitable electrolyte. 25- hydroxycholesterol provides anodic signal at the potential of +1500 mV and 7-ketocholesterol at +1900 mV in that media. Electrochemical reduction of 7-ketocholesterol was also studied. However, the observed cathodic signal isn't reproducible. The stability of oxysterols in the presence of perchloric acid was confirmed by UV-VIS spectroscopy. Calibration dependence of oxysterols was measured using differential pulse voltammetry and resulted in the limit of detection of 0.82 µmol l−1 for 25-hydroxycholesterol and 0.66 µmol l−1 for 7-ketocholesterol. In the second part of the thesis, an HPLC method was developed for the separation of a sterol mixture on a reversed-phase C18 column using a mobile phase containing 50 mmol l−1 sodium perchlorate in acetonitrile with 0% or 6% water...
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Electrochemistry of Acetaminophen
Mikysek, T. ; Ludvík, Jiří
The contribution is focused on electrochemical oxidation of acetaminophen mainly in non-aqueous media. The influence of various organic solvents as well as the pH effect is described herein. The redox properties of acetaminophen were studied by means of cyclic voltammetry, and rotating-disk voltammetry. We found that the protonation/deprotonation of acetaminophen acts as a ratedetermining step, where the stability of phenoxy radical intermediate plays an important role.
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Study of DNA-doxorubicine interaction by electrochemical methods on nanostructured electrodes
Přibyl, Jakub ; Fohlerová, Zdenka (referee) ; Kynclová, Hana (advisor)
Cancer diseases are one of the leading causes of mortality worldwide, for this reason, great attention anticancer drugs. Doxorubicin falls into the category of the most widely used cancer drugs. The method of electrochemical impedance spectroscopy were investigated properties of golds electrodes without deposit nanoparticles and electrodes with deposit gold nanoparticles. Using voltammetric measurements we detected doxorubicin and investigated the interaction of doxorubicin with oligonucleotides on gold electrodes without nanoparticles and electrodes modified with gold nanoparticles.
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Thick-film sensors for heavy metals detection
Gajdoš, Libor ; Majzlíková, Petra (referee) ; Prášek, Jan (advisor)
This project describes the possibilities of heavy metals detections in solutions using differential pulse voltammetry with tree-electrode electrochemical thick-film sensors. In the theoretical part, the thick-film technology is described as well as thick-film pastes’ types and compositions, followed by introduction to electrochemistry and electro-analytical methods of measurement. This project also describes the three measured heavy metals – cadmium, lead and copper. In the practical part, heavy metals’ ions detection in solutions using carbon working electrode and determination of the detection limit and sensitivity are described and discussed. Finally the evaluation of obtained results and results comparison to hygienic limits are included.
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Preparation and characterisation of ceramic electroactive materials for Na-ion batteries
Vaněk, Martin ; Libich, Jiří (referee) ; Čech, Ondřej (advisor)
Hlavním cílem této práce je charakterizace vzorků titanátů, jako materiálů pro sodíko-iontové (Na-ion) akumulátory. Syntéza některých vzorků je součástí této práce. Charakterizace je zaměřena na elektrochemické vlastnosti, složení a morfologii použitých materiálů. První část se zabývá lithium-iontovými (Li-ion) akumulátory. Byly vybrány, protože jsou ve vědeckých článcích dobře popsány a základní funkční princip je aplikovatelný také na Na-ion akumulátory. Materiály používáné pro katody, anody a elektrolyty následují po krátké části shrnující parametry a konstrukci Li-ion akumulátorů. Následující kapitola je zaměřena na sodíko-iontové akumulátory. Srovnání sodíku a lithia je následováno materiály používanými pro elektrody a elektrolyty (s důrazem na anodové materiály). Třetí část popisuje analytické metody použité pro charakterizaci elektrod a materiálů. Jedná se o elektrochemickou charakterizaci (cyklická voltametrie a galvanostatické cyklování s potenciálovým omezením), morfologii (rastrovací elektronová mikroskopie) a složení (X-ray difrakční spektroskopie). Poslední dvě kapitoly obsahují syntézu a charakterizaci sodného titanátu a charakterizaci dvou vzorků TiO2. Výsledky této práce jsou shrnuty v závěru.
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Hair as a bioindicator of contamination of risk metals
Zmijová, Marie ; Řezáčová, Veronika (referee) ; Zlámalová Gargošová, Helena (advisor)
The use of hair as a bioindicator of environmental contamination by risk elements is becoming more and more common. This bachelor thesis deals with the use of this matrix for analysis using the voltammetric method. It focuses on the optimization of the method for determining the concentration of cadmium, copper, lead and zinc in real hair samples and monitors the effects on the incorporation of these elements into the hair fiber. The presence of zinc and copper was confirmed in all samples analyzed. Cadmium could only be quantified in one sample. The effect of gender and age on the concentration of elements has not been demonstrated. Concentration of lead has been linked to smoking, with higher concentrations found in smoker’s hair than in non-smoker’s.
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Optimization of thick-film electrochemical sensor's electrode system
Cupal, Miroslav ; Adámek, Martin (referee) ; Prášek, Jan (advisor)
Master’s thesis deals with thick/film sensor’s electrodes optimization. The aim of this work is to determine how the geometric size and shape of the electrodes affect the output current response. Technology and electro-analytical method is described in the theoretical part. The practical part is aimed at thick-films electrodes and sensors optimalization. It is here each optimization TLV electrodes in terms of their impact on the size of the output current response three-electrode electrochemical system using standard electrodes. Similarly, there is a study of the effect size performed on one common electrode free-electrodes sensor. Finally, there are studied various forms of electrode area three-electrode thick-film sensor in terms of their effect on the output current response. Summarized results are described in the final part of the work.
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