3-STAGE SEQUENTIAL EXTRACTION PROCEDURE FOR THE DETERMINATION OF METALS IN RIVER SEDIMENTS

A three-stage sequential extraction procedure, following a protocol pr oposed by a European working group coordinated and supported by the Co mmunity Bureau of Reference (BCR), has been applied to two river sedim ents from an industrial region of East Catalonia, Spain. The extractan t solutions were: Step One, acetic acid (0.11 mol l(-1)); Step Two, hy droxylammonium chloride (0.1 mol l(-1), pH 2); Step Three, hydrogen pe roxide (8.8 mol l(-1)) oxidation followed by extraction with ammonium acetate (1 mol l(-1), pH 2). The six elements determined in the extrac ts were Cd, Cr, Cu, Ni, Pb and Zn. Analysis of the extracts was carrie d out by flame atomic absorption spectrometry (FAAS). There were sligh t differences in analyte sensitivity between calibrants prepared in th e extractant matrices and acidified aqueous calibrants. No significant matrix interferences were found except for Cr in the acetic acid and hydroxylammonium chloride extracts, which required determination by th e standard additions method. The other elements (plus all the elements in the ammonium acetate extracts) were determined by direct calibrati on against calibrant solutions prepared in the same matrices as the sa mples.