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

A differential pulse voltammetric (DPV) procedure is proposed for the speci ation of aluminium in natural waters using Pyrocatechol Violet chemically m odified electrodes (PCV-CMEs). This novel speciation idea is based on the s elective determination of different Al-III forms under two pH conditions. T he labile monomeric At fraction (mainly inorganic Al) is analysed at pH 4.8 (0.20 mol dm(-3) NaOAc-HOAc) and the total monomeric Al fraction is analys ed 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 wat ers sampled from different regions of China. Five fractions are measured di rectly or indirectly: (i) labile monomeric Al. (ii) total monomeric Al. (ii i) 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.