Speciation of aluminium(iii) in natural waters using differential pulse voltammetry with a Pyrocatechol Violet-modified electrode

Abstract

A differential pulse voltammetric (DPV) procedure is proposed for the speciation of aluminium in natural waters using Pyrocatechol Violet chemically modified electrodes (PCV-CMEs). This novel speciation idea is based on the selective determination of different Al^III forms under two pH conditions. The labile monomeric Al fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm⁻³ NaOAc–HOAc) and the total monomeric Al fraction is analysed at pH 8.5 (0.20 mol dm⁻³ NH₃·H₂O–NH₄Cl). The difference is thought to be caused by the weak competition ability of PCV to sequester Al^III from Al^III–natural organic matter complexes. This sensitive and simple speciation method has been applied successfully to aluminium speciation in natural waters sampled from different regions of China. Five fractions are measured directly or indirectly: (i) labile monomeric Al; (ii) total monomeric Al; (iii) acid reactive Al; (iv) non-labile monomeric Al; and (v) acid soluble Al. The results are in satisfactory agreement with those obtained by Driscoll’s 8-hydroxyquinoline extraction–ion exchange method.