Aluminum speciation by means of anion chromatography and coupled anion/cation chromatography

Abstract

Anion chromatography had been applied to the speciation of synthetic aluminum solutions containing medium to strong ligands. A gradient elution based on a chloride start eluent and a perchlorate final eluent allowed the separation of neutral or cationic and of negatively charged Al species. The separation of Al species with a nominal charge of −1, −2 and −3 or higher required a run time of less than 10 min. The ligands investigated were fluoride as monodentate, oxalate as bidentate and citrate as tridentate anion in binary, ternary or quaternary mixtures at different pH values. The results of anion chromatography are compared to those obtained by calculation methods and by cation chromatography. Anion chromatography turned out to be a useful tool for the speciation of Al solutions containing strong ligands such as citrate, whereas anionic Al–oxalate and Al–fluoride species are at least partially disintegrated. The favorite detection technique is on-line coupling with atomic spectrometry. An attempt to overcome the limitations of either anion or cation chromatography is the combination of both methods in a single chromatographic procedure. A slight modification of the methods used for anion and cation separation allowed a complete speciation of Al solutions within 20 min.