Vanillylmandelic and Homovanillic acid: Electroanalysis at non-modified and polymer-modified carbon-based electrodes

The electrochemical behaviour of two main catecholamine metabolites serving as diagnostic tumour biomarkers, homovanillic acid (HVA) and vanillylmandelic acid (VMA), on anodically oxidized boron doped diamond (BDD) electrodes, non-modified glassy carbon electrodes (GCE), and GCE modified by polymers, namely by Nafion (Nafion/GCE) and by poly(neutral red) (PNR/GCE), was investigated. The voltammetric responses of both biomarkers are strongly dependent on pH of the aqueous buffer solution and electrode material used. BDD electrodes exhibit more positive oxidation potentials and lower current densities for oxidation of both analytes, depending also on the surface termination. Concentration dependences were measured in 0.1 mol L⁻¹ phosphate buffer pH 3.0, as 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 electrodes, non-modified GCE, Nafion/GCE, and PNR/GCE, respectively. The limits of quantification for both organic compounds on all tested electrode materials are sufficiently low for their determination in urine. Verification of the possibility of simultaneous voltammetric determination of the studied biomarkers in the mixture was also carried out.