Stripping voltammetric determination of zinc ions using a graphite-based electrochemical sensor modified with Alizarin Red S.

A simple, low-cost, and sensitive electrochemical sensor was developed for the determination of zinc ions by anodic stripping voltammetry (ASV). The sensor (denoted G/W/ARS/MES) consists of a graphite-wax paste modified in situ with Alizarin Red S (ARS). The nature of the Zn-ARS interaction was examined by quantum-chemical calculations together with FT-IR and UV-Vis spectroscopy, which consistently indicated coordination of Zn(II) through the hydroxyl and carbonyl groups of ARS. Under optimised conditions-a universal buffer of pH 4.5-5.5, a 0.1 M H3PO4 + 0.1 M KNO3 supporting electrolyte and an 80 s accumulation time-the modified sensor produced a well-resolved Zn(II) stripping peak at - 1040 mV, shifted by about 280 mV from that of the unmodified electrode and clearly separated from the signals of Cd(II), Pb(II), and Cu(II). The peak current varied linearly with concentration over the range 2.0-35.0 µg L-1 (R2 = 0.9910), with a detection limit of 0.57 µg L-1. The method showed good repeatability and high selectivity and was applied to the determination of trace Zn(II) in waste, ground, and industrial-zone waters and in agricultural soils of the Jizzakh and Tashkent regions. The results agreed well with those obtained by atomic absorption spectrometry, confirming the accuracy of the proposed method.