DETERMINATION OF MONONUCLEAR DISSOLVED ALUMINUM IN NEAR-NEUTRAL WATERS

Concentrations of mononuclear dissolved Al are determined in samples of natural waters and of solutions separated from experimental suspensions of clay minerals, by solvent extraction and spectrophotometry of aluminum 8-hydroxyquinoline. Samples are treated with a solution of 8-hydroxyquinoline buffered at pH 5.0 by sodium acetate-acetic acid. The resulting Al-hydroxyquinoline complex is extracted immediately into 2.00 ml toluene, to prevent inclusion of secondary mononuclear Al released from poly-nuclear Al(OH)x ions or aluminous solids. After centrifugation-separation of the toluene and aqueous phases, the overlying toluene layer is transferred to a spectrophotometer equipped with a miniature fixed quartz cell. A detection limit of 0.2 μg Al l-1 can be attained with 100-ml samples, and at 1.0 μg Al l-1, the analytical uncertainty is ± 10% or less. Preliminary extractions with chloroform solutions of diethylammonium diethyldithiocarbamate eliminate interferences due to dissolved V, Fe, Ni, Cu, Ga, Mo and U. Extracting the Al-hydroxyquinoline complex at pH 8.3 eliminates any interference due to F. The procedure was used to measure the solubility of gibbsite over the pH range 5-8. © 1979.