Chromium speciation in water by electrothermal AAS after simultaneous adsorption of Cr(III) and Cr(VI) on an activated alumina mini column

A simple and sensitive method has been developed for species selective dete rmination of Cr(III) and Cr(VI) in water by electrothermal atomic absorptio n spectrometry (ET-AAS). Both species are adsorbed on a mini column packed with activated alumina at pH 7 using NH4Cl/NH4OH buffer. Cr(III) and C(VI) are eluted by using 1 M HNO3 and 1 M NH3 solutions, respectively. The activ ated alumina was preequilibrated with buffer at pH 7, before loading the co lumn. Elution efficiency of 98-103% has been observed for Cr(VI) and 65-75% for Cr(III). Preconcentration of nearly 40 times was achieved providing a detection limit of 0.01 mu g/L for Cr(VI) and 0.016 mu g/L for Cr(III) in d eionized water. Better than 10% precision was obtained in the range of 0.1-0.2 mu g/L. The method has been applied for chromium speciation in natural water reference material BCR RM 544 and rainwater samples.