Development of a method for chromium speciation by selective solid phase extraction and preconcentration on alumina-functionalized thiosemicarbazide

A speciation method is developed for Cr(III) and Cr(VI) at selected medium pH range via solid phase extraction on three designed and synthesized chelating inorganic solid sorbents based on adsorption of thiosemicarbazide, as the nitrogen and sulfur containing chelating compound, on alumina surface [Al-TSC (I-III)]. The influence of various parameters including medium pH, time of contact, and interference of matrix and coexistent elements on the speciation and selective extraction processes of chromium species are studied and evaluated on the basis of determination of the metal adsorption capacity, distribution coefficient, and separation factor. Quantitative recovery of Cr(VI) was accomplished by [Al-TSC (I-III)] at pH=1.0, while Cr(III) was found to be recovered on these sorbents at pH=7.0 with minimal or no interference between these two species under the studied buffering conditions. The proposed method has been successfully applied for speciation, selective extraction, and preconcentration of Cr(III) and Cr(VI) in water samples with a preconcentration factor of 200.