Direct Determination of Aluminum and its Cationic Fluoro‐Complexes by Ion Chromatography

Abstract

Abstract An ion chromatographic method was developed for the direct determination of monomeric Al (Al 3+ , and hydroxo‐, sulfato‐, oxalato‐, and fluoro‐ complexes). Separations were made in one run in 4 min with a 50 mm low‐capacity cation exchange column, and detected by postcolumn reaction with pyrocatechol violet. Three peaks corresponding with mono‐, di‐ and trivalent species were obtained. The last peak also included the hydroxo‐Al and sulfato‐Al species. The AlF 2+ species could be determined directly, but AlF + 2 coeluted with the monovalent oxalato‐ species. Citrato‐Al species were not detected because of the inability of pyrocatechol to decouple the complex in the time frame of the analysis. Concentrations of Al down to 2 µ M could be determined with 200 µL injections. The results for 21 Al‐F solutions closely matched those predicted from a chemical equilibrium program. The method was applied to extracts of 10 soils and it was found that Al 3+ , including hydroxo‐Al species, and AlF 2+ were dominant. Limitations to the application of the method to soils included coelution of AlF + 2 with monovalent organic species that are able to be decoupled by pyrocatechol, and blockage of the column end frits by solutions containing more than 200 mg L −1 of humic acid. The ion chromatographic method is the first to directly determine AlF 2+ and other well‐defined forms of monomeric Al. It is rapid and can be fully automated.