DETERMINATION OF CADMIUM IN SOIL EXTRACTS CONTAINING HIGH-LEVELS OF IRON AND ALUMINUM BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROPHOTOMETRY

Accurate determination of trace levels of cadmium (Cd) in soil extract s can become problematic in an extractant such as acid oxalate which r eleases a substantial amount of an interfering element, especially iro n (Fe) along with trace levels of Cd from soils. The most common techn ique to identify the chemical interference is to check the recoveries of the element of interest (e.g., Cd), by adding a known concentration to the extract and analyzing. This study evaluated several published methods {solvent extraction with MIBK (methyl iso-butyl ketone) follow ing reaction with APDC (ammonium pyrrolidine; matrix modification with palladium/magnesium nitrate [Pd/Mg(NO3)(4)]; monoammonium phosphate ( NH4H2PO4); nitric acid (HNO3) + molybdenum (Mo) + hydrogen peroxide (H 2O2) or palladium nitrate [Pd(NO3)(2)/ammonium nitrate (NH4NO3)]} reco mmended for analyzing trace levels of Cd in soils using graphite furna ce atomic absorption spectrophotometry (GFAAS). None of these methods were found suitable for analyzing trace levels of Cd extracted by acid ified ammonium oxalate [(NH4)(2)C2O4] extracts or mixed acid digests. The recovery of added Cd in these extracts was consistently below 80% and relative standard deviations were in the range of 1-17%. A simple method for analyzing trace levels of Cd, based on iodide complexation and extraction into MIBK, was developed and is recommended for soil ex tracts encountering chemical interference especially from Fe. The reco veries of Cd were found to be 100+/-10% and the coefficient of varianc e was minimal.