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 AlIII for SVRS and natural organic matter (NOM) present in natural waters at two pHs: pH 5.2 and 8.5. The Labile monomeric Al fraction (mainly inorganic Al) is determined at pH 5.2 condition (accumulation time: 60s, accumulation potential: -0.33V, SVRS concentration: 1.0×10-6moldm^-3 and NH4Ac-HClO4 concentration: 0.17moldm^-3), while the total monomeric Al fraction is determined at pH 8.5 condition (accumulation time: 30s; accumulation potential: -0.47V; SVRS concentration: 3.0× 10-6moldm^-3 and NH4Ac-NH3·H2O concentration: 0.17moldm^-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 (Alr); (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.