The voltammetric oxidation of hypoxanthine, xanthine, and uric acid was investigated by means of linearsweep voltammetry, cyclic voltammetry, and controlled-potential coulometry. Hypoxanthine, xanthine, and uric acid each gave a single oxidation peak at a different potential, with a stationary glassy carbon electrode, over the wide pH range of 0–13. Hypoxanthine was initially oxidized in a two-electron step to xanthine, which was then further oxidized in a two-electron step to uric acid, as well as the enzymatic oxidation. All three substances were strongly adsorbed on the surface of the glassy carbon electrode, so that the concentration vs .anodic peak current curves were not linear. The adsorption on the electrode was very dependent on the pH, and especially at pH values around neutrality the anodic peaks were ill-defined. However, in such acid solutions as H3PO4 and H2SO4, the voltammetric oxidation was a diffusion-controlled process and the differences between the peak potentials were most pronounced (ca. 400 mV). Consequently, it was possible to determine simultaneously three hydroxypurine bases by using 1 M H2SO4 or 1 M H3PO4 as a supporting electrolyte, without prior treatment or separation procedures.

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Adenine, adenosine, guanine, and guanosine were voltammetrically oxidized in a glassy carbon electrode in aqueous solutions, but at different potentials. In general, the nucleosides were oxidized at more positive potentials than their bases. The bases and their nucleosides were strongly adsorbed on the surface of the glassy carbon electrode at the pH values around neutrality, so that the concentration vs. anodic peak current curves were not linear. The adsorption on the electrode was very dependent on the pH, and at pH values below 4 good linear relationships were observed between the anodic peak current and the concentration. The differences between the peak potentials of each of the purine bases and their nucleosides were most pronounced at pH 2–4. Consequently, it was possible to determine simultaneously both in mixtures of the purine bases and their nucleosides by using Britton-Robinson buffer as a supporting electrolyte in the pH range of 2–4. The proposed method is simple and rapid, since no prior treatment or separation procedure is required.

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