Determination of the speciation of aluminum(III) in natural waters by adsorption stripping voltammetry and complexation with AlIII-solochrome violet RS

A sensitive electrochemical procedure is proposed for the determination of the speciation of aluminum in natural waters using solochrome violet RS (SVRS) as analytical agent. The method is based on the different affinity of Al-III for SVRS and natural organic matter (NOM) present in natural waters at two pHs: pH 5.2 and 8.5. The Labile monomeric At fraction (mainly inorganic At) is determined at pH 5.2 condition (accumulation time: 60 s, accumulation potential: -0.33 V, SVRS concentration: 1.0 x 10(-6) mot dm(-3) and NH4Ac-HClO4 concentration: 0.17 mot dm-3), while the total monomeric At fraction is determined at pH 8.5 condition (accumulation time: 30 s; accumulation potential: -0.47 V SVRS concentration: 3.0 x 10(-6) mot dm-3 and NH4Ac-NH3.H2O concentration: 0.17 mot dm-3). This sensitive and simple speciation method is successfully applied to the speciation of Al in natural water samples. Five fractions are measured: (i) labile monomeric Al (Ali); (ii) total monomeric Al (Ala); (iii) acid reactive Al (Air); (iv) non-labile monomeric Al (Alo); (v) acid soluble Al (Als). The results are satisfactorily in agreement with those of the 8-hydroxyquinoline extraction/ion exchange method. The proposed method possesses the distinct advantages of speed, convenience, simple instrumentation, and freedom from toxic solvents. The principle for speciation of Al by electrochemical method is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.