THE DIFFERENTIATION OF LEAD IN SOIL ORGANIC MATTER USING SEQUENTIAL EXTRACTION PROCEDURE AND THE DETERMINATION BY ELECTROTHERMAL ATOMIC ABSORPTION SPECTROMETRY

The five-step sequential extraction procedure for fractionation of lead has been applied to reference materials of soils with certified total lead contents. The extractant solutions were I mol L-1 ammonium acetate, 1 mol L-1 hydroxylammonium chloride in 25 % acetic acid (1:1), 0.1 mol L-1 hydrochloric acid, 0.5 mol L-1 sodium hydroxide, and 8 mol L-1 nitric acid. The residue was decomposed by HF and HNO3. Using this procedure, the metal fraction bound to the organic matter can be distinguished. The determination of lead in the soil extracts was performed by ETAAS. The measurement conditions were optimized for every individual soil extract in the presence of various matrix modifiers (NH4H2PO4; NH4H2PO4+Mg(NO3)(2), NH4H2PO4+Pd(NO3)(2); and Mg(NO3)(2)+Pd(NO3)(2)). Accuracy was assessed by comparing the sum of the contents of lead in individual soil extracts and in the residual fraction with the total certified values used (certified reference materials (CRMs) of soils). The overall recovery values for lead were 101-112%.