AMMONIUM ACETATE EXTRACTS AND THEIR ANALYSIS FOR THE SPECIATION OF METAL-IONS IN SOILS AND SEDIMENTS

The use of ammonium acetate (1 mol/l at pH 7) extraction of soils and sediments for the speciation of metal ions is briefly discussed. Becau se the sensitivity of flame atomic absorption spectrometry (FAAS) is i nsufficiently sensitive for the determination of many of the heavy met als in ammonium acetate extracts of unpolluted, and even in some pollu ted soils, the use of electrothermal atomic absorption spectrometry (E TAAS) was studied. A general procedure, using graphite furnace atomisa tion and the ''universal'' matrix modifier, palladiun, was developed, that was sufficiently sensitive for the determination of Cd, Cr, Cu, N i, Pb and Zn even in unpolluted soils. The concentration of zinc, howe ver, will almost always be high enough for determination of FAAS and t his method is to be preferred to ETAAS for this element. While, for Cr , Cu, Ni and Pb, direct calibration with external standard solutions i s practicable, it is necessary to use the standard additions calibrati on method for cadmium, to avoid matrix interference effects. The stand ard additions technique is recommended, however, because it compensate s for real differences in the operating parameters of different instru ments set to the same nominal values. This is particularly important f or interlaboratory comparisons or for certification analyses in the pr eparation of reference materials.