Ultra-Sensitive Anodic Stripping Voltammetry for the Determination of Xanthine at a Glassy Carbon Electrode

Abstract.

An electrochemical anodic stripping procedure for ultra-trace assay of xanthine in Cu²⁺ solution at a glassy carbon electrode (GCE) is described. Cyclic voltammetry was used to characterize the nature of the process taking place at the GCE. The anodic stripping response in the presence of Cu²⁺, at 150 mV (peak I) and 600 mV (peak II), is evaluated with respect to various experimental and instrumental conditions. Voltammetric studies show that the mechanism of the overall reaction is similar to that of the oxidation of purine derivatives at a pyrolytic graphite electrode. It is found that the copper metal deposited onto the GCE was oxidized to Cu⁺ at around −180 mV vs. Ag/AgCl and the generated Cu⁺ reacted with xanthine to accumulate on the GCE as an insoluble compound. The Cu⁺-xanthine compound accumulated on the GCE was redissolved by the oxidation of Cu⁺ to Cu²⁺ at ca. 150 mV, and the concentration of xanthine in the vicinity of the GCE increased. The results enabled us to use the measurement of the oxidation peak current as the basis of a simple, accurate and rapid method of determining xanthine within a concentration range of 19.9 to 166 nM for peak (I) and 0.24 to 17.2 µM for peak (II). Promising results were obtained for xanthine determination by using an external mixing step prior to stripping measurements, which yielded a detection limit of 0.138 µg L⁻¹ (9.1×10⁻¹⁰ M) xanthine. The effect of some interferences (e.g. purine compounds, amino acids and some metal ions) was considered.