Voltammetric determination of clinical markers vanillylmandelic and homovanillic acid at boron-doped diamond electrode

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