Characterization of stable aluminium-citrate species as reference substances for aluminium speciation by ion chromatography.

Well-defined anionic aluminium-citrate species are accessible from crystalline aluminium complexes. The solution chemistry of those species can be investigated using ion chromatography as a powerful tool for aluminium speciation in aqueous samples. The separation of three anionic aluminium-citrate complexes by anion exchange chromatography is possible within 5 min using isocratic conditions. The element specific detection was done by online coupled ICP-AES. The remaining charge of the complexes after dissolution can be determined by ion chromatography using a retention model. Time-dependent monitoring of the species distribution gave information about the species stabilities and the decomposition pathways. With citric acid as an aluminium chelator partially very stable anionic species are observed. These complexes are important components in biological systems. An example for the practical use of the separation method and the well-defined standards is given for plant sap, which showed two species with similar behavior compared to the investigated stable aluminium-citrate complexes.