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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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Vanillylmandelic and Homovanillic Acid: Electroanalysis at Carbon-Based Electrodes
Baluchová, Simona ; Schwarzová, Karolina (advisor) ; Dejmková, Hana (referee)
The objective of the present work is the study of the electrochemical behaviour of two diagnostic tumor markers of great importance, vanillylmandelic acid (VMA) and homovanillic acid (HVA), on carbon-based electrodes by using cyclic and differential pulse voltammetry. A comparison was made among non-modified glassy carbon electrode (GCE) and GCE modified by multi-walled carbon nanotubes, Nafion (Nafion/GCE) and poly(neutral red) (PNR/GCE), and further boron doped diamond (BDD) electrode which was activated by anodic polarization (Eakt = +2,4 V, t = 30 s) or by polishing on alumina slurry. Significant differences in the voltammetric responses of VMA and HVA were found, not only among utilized electrode materials which also influenced the way of controlling the oxidation process, but also they depend on the pH value of aqueous media in which these acids occurred. An acidic environment is the most suitable for their determination. Calibration dependences were measured in 0.1 mol∙l−1 phosphate buffer pH 3.0 which was chosen as an optimal supporting electrolyte for differential pulse voltammetric determination. Achieved detection limits were 0.6, 0.9, 0.8 and 1.2 μmol∙l−1 for HVA and 0.4, 1.5, 2.4 and 1.1 μmol∙l−1 for VMA at BDD electrode, non-modified GCE, Nafion/GCE and PNR/GCE, respectively. Limits...
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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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