Ammonium Acetate Extracts and Their Analysis for the Speciation of Metal Ions in Soils and Sediments

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Abstract
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. Because the sensitivity of flame atomic absorption spectrometry (FAAS) is insufficiently sensitive for the determination of many of the heavy metals in ammonium acetate extracts of unpolluted, and even in some polluted soils, the use of electrothermal atomic absorption spectrometry (ETAAS) was studied. A general procedure, using graphite furnace atomisation and the “universal” matrix modifier, palladium, was developed, that was sufficiently sensitive for the determination of Cd, Cr, Cu, Ni, Pb and Zn even in unpolluted soils. The concentration of zinc, however, will almost always be high enough for determination of FAAS and this method is to be preferred to ETAAS for this element. While, for Cr, Cu, Ni and Pb, direct calibration with external standard solutions is practicable, it is necessary to use the standard additions calibration method for cadmium, to avoid matrix interference effects. The standard additions technique is recommended, however, because it compensates for real differences in the operating parameters of different instruments set to the same nominal values. This is particularly important for interlaboratory comparisons or for certification analyses in the preparation of reference materials.