Speciation of aluminum in aqueous solutions using ion chromatography

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Abstract
An ion chromatographic method in which aluminum (Al) is quantitatively determined via postcolumn derivatization with Tiron (4,5-dihydroxy-m-benzenedisulfonic acid) was evaluated for its utility as a method for speciating Al in aqueous solutions. Fluro-, oxalato-, and citratoaluminum compexes were identified by distinct peaks within chromatograms of Al solutions when the appropriate ligand was added. Excellent quantitative agreement between predicted species concentrations (via the thermodynamic speciation model GEOCHEM) and those determined by ion chromatography was obtained for samples prepared in the eluent matrix. The predominantly outer sphere sulfatoaluminum complexes were not observed to elute as singly charged species, but rather exhibited a retention time indistinguishable from the Al(H2O)63+ species. It is concluded that inner sphere Al complexes (generally possessing relatively high association constants) possess adequate kinetic stability to withstand degradation during the ion exchange process, whereas outer sphere complexes apparently readily dissociate in the presence of the sulfonate exchange sites. Deviations in sample ionic strength (.mu.) and pH from that of the eluent resulted in some redistribution among species, the degree of which was ligand specific.