COMPARISON OF 2 METHODS OF SAMPLE PREPARATION FOR DETERMINATION BY ATOMIC-ABSORPTION SPECTROPHOTOMETRY OF HEAVY-METALS IN SOILS AND SEDIMENTS

Two commonly used methods of dissolution of heavy metals in soils and sediments for atomic absorption spectrophotometry (AAS) determination were compared. Dry ashing and subsequent dissolution with 3 N HCl in a block digestor was shown to give a better estimate of the aqua regia-soluble fraction than wet ash digestion with a mixture of HNO3 and HClO4 acids using reference materials. But both methods extracted significantly less than the certified total contents of most metals. In soils and sediments from SW Spain, the amounts extracted by the block heater method were generally greater than those obtained by wet ash digestion. In agricultural soils, highly significant differences were found between the amounts of Fe, Cu, and Zn extracted by both methods, but the significance decreases if both methods are used on soils or sediments from mining areas where metal contents are likely to be from recent deposits.