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Utilization of carbon-based solid electrodes to electrochemical oxidation of acyclovir
Vaněčková, Eva ; Schwarzová, Karolina (advisor) ; Fischer, Jan (referee)
Electrochemical oxidation of acyclovir at glassy-carbone electrode and boron-doped diamond electrode gives one pH-dependent oxidation signal; the corresponding electrode reaction is controlled by diffusion. It is followed by a second indistinctive signal in the pH range 2,0 - 9,0. Further, optimization of conditions was carried out for determination of acyclovir using DC and DP voltammetry. The calibration dependence on GC electrode in B−R buffer (pH = 6,0) is linear only in the concentration range from 2 to 10 μmol∙l−1 for DCV with limit of detection 0,38 μmol∙l−1; for DPV it is not linear. BDD electrode has to be activated to prevent its passivation. Anodic activation at +2,4 V for 15 s with simultaneous stirring of solution results in relative standard deviation of 0,9% for acyclovir concentration of 1∙10−4 mol∙l−1. Using DCV and DPV methods linear concentration dependences were obtained in 0,1 mol∙l-1 nitric acid and in pH 6,0 B−R buffer. The lowest limit of detection and limit of quantification (LOD = 0,47 μmol∙l−1 a LOQ = 1,55 μmol∙l−1) and linear range from 0,6 to 100 μmol∙l−1 was reached in pH 6,0 B−R buffer. Further, standard addition method was used to quantify acyclovir in Zovirax tablets. Satisfactory recoveries of 101,1 ± 2,3 % using DCV and 98,8 ± 2,2 % using DPV at BDD (compared with the...
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Voltammetric determination of clinical markers vanillylmandelic and homovanillic acid at boron-doped diamond electrode
Baluchová, Simona ; Schwarzová, Karolina (advisor) ; Zima, Jiří (referee)
This thesis investigates electrochemical oxidation of two main catecholamine metabolites vanillylmandelic and homovanillic acid at anodically oxidized boron-doped diamond electrode using voltammetric techniques. Their behavior in aqueous media depends on its pH value significantly; the highest and best developed voltammetric signals are provided in an acidic medium when both organic compounds occur in their non-ionized form. The phosphate buffer pH 3.0 was chosen as supporting electrolyte for analysis of these two substances and the conditions of determination were optimized. Calibration dependences are linear for both studied compounds in the concentration range from 4 to 100 μmol∙l−1 . Using differential pulse voltammetry limits of detection for homovanillic acid (LOD = 0.57 μmol∙l−1 ) and for vanillylmandelic acid (LOD = 0.41 μmol∙l−1 ) were achieved. The possibility of their simultaneous determination at boron-doped diamond was also verified. The oxidation mechanisms of homovanillic acid and vanillylmandelic acid at boron-doped diamond electrode were studied by cyclic voltammetry and in both cases it is diffusion-controlled reaction.
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Study of electrochemical behaviour of quinine and cinchonidine at boron doped diamond electrode
Brunovská, Veronika ; Schwarzová, Karolina (advisor) ; Nesměrák, Karel (referee)
In this thesis, it was for the first time studied the electrochemical behaviour of cinchona alkaloids quinine and cinchonidine by cyclic voltammetry and differential pulse voltammetry using boron doped diamond (BDD) thin film as an electrode material. Cyclic voltammograms did not exhibit any significant anodic signals corresponding to a simple electrode reaction. However, current increase with indistinctive maxima compared to the basic electrolyte was recorded in Britton - Robinson buffers with pH 2,0 − 12,0 medium. Accordingly, insignificant signals observable in the cathodic area at far negative potential close to the potential of decomposition of the supporting electrolyte , presumably to the reduction of quinoline skeleton. It was found by means of differential pulse voltammetry that the number of those observable current maxima varies for quinine and cinchonidine in different supporting electrolytes. Quinine provided the best developed anodic peaks in the medium of BR buffer pH 5,0 and 6,0 and cinchonidine in pH 7,0, 9,0 and 12,0. The calibration dependence of anodic peak of quinine in BR buffer pH 5,0 is linear in the concentration range 6∙10−6 mol∙l−1 − 1∙10−4 mol∙l−1 with limit of quantitation 4,39∙10−6 mol∙l−1 . In the cathodic area the limit of quantitation is 4,33∙10−5 mol∙l-1 . The...
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