Sequential extraction of trace metals from sediments

With the aim of harmonizing the methodology associated with the trace metal partitioning in sediments, a group of European researchers proposed a three-step sequential extraction scheme using acetic acid, hydroxylamine hydrochloride and ammonium acetate as extracting agents. The metal content in each extract is mainly determined by AAS or ICP.In this paper, the validation of chromium determination in the extracts by AAS is described. The optimum instrumental conditions and the matrix effects of the different reagents used in the extraction scheme are studied for Cr(III) and Cr(VI) solutions by FAAS and ETAAS techniques. The effect of the concomitant species are also studied in the different extracts. The interfering effects are minimized by means of releaser agent for FAAS.The addition of 1% oxine is recommended for acetic acid and hydroxylamine extracts, whereas for step 3 the use of a releaser agent is not necessary. For ETAAS, the use of a calibration graph with pyrolytically-coated tubes gave satisfactory results.The procedure of analysis is applied to chromium partitioning in two sediments with certified total chromium content and to different sediments from Rio dos Sinos of Brazil.From the results obtained it is recommended to measure chromium contents in steps 1 and 2 by ETAAS and the content of step 3 by FAAS.