Speciation analysis of Sb(III) and Sb(V) by adsorptive stripping voltammetry in the presence of Pyrogallol red

Abstract

This work presents an adsorptive stripping voltammetric method for the speciation of antimony based on the formation of their complexes with Pyrogallol red (PGR). Both Sb(III) and Sb(V) form complexes with PGR, however Sb(III) forms complex rapidly whereas Sb(V) forms complex very slowly. After the Sb^V-PGR complex is formed, on the surface of the mercury electrode is reduced to Sb^III-PGR. Then the electrochemical signal is the reduction of Sb^III-PGR complex to Sb(0). The variation of peak current with pH, accumulation time (t_acc), accumulation potential (E_acc), and PGR concentration (C_PGR) were optimized. The best experimental conditions for Sb(III) were pH: 2.2 (0.1 mol L⁻¹, Phosphate buffer, PB), C_PGR: 3.0 μmol L⁻¹, and E_acc: −0.10 V obtaining a detection limit (DL) of 1.1 μg L⁻¹ (t_acc: 35 s). When measured at 2 h, the signal of the Sb^III-PGR complex is almost the same and now it is possible to appreciate the increase in the signal due to presence of Sb^V-PGR complex, previously reduced to Sb^III-PGR in the Hg electrode. This allows us to determine the total concentration of antimony. The developed method was validated by the determination of Sb(III) in spiked drinking water from the laboratory and spiked synthetic seawater with relative errors of less than 5.0 %. The method was successfully applied to the determination of Sb(III) and Sb_total in an Industrial waste liquid sample comparing the results of Sb_total by ICP-OES technique (RE: 0.6 %).