Determination of cadmium in soil extracts containing high levels of iron and aluminum by graphite furnace atomic absorption spectrophotometry

Abstract

Accurate determination of trace levels of cadmium (Cd) in soil extracts can become problematic in an extractant such as acid oxalate which releases a substantial amount of an interfering element, especially iron (Fe) along with trace levels of Cd from soils. The most common technique 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) following reaction with APDC (ammonium pyrrolidine; matrix modification with palladium/magnesium nitrate [Pd/ Mg(NO₃)₄J; monoammonium phosphate (NH₄H₂PO₄); nitric acid (HNO₃) + molybdenum (Mo) + hydrogen peroxide (H₂O₂) or palladium nitrate [Pd(NO₃)₂/ammonium nitrate (NH₄NO₃)]} recommended for analyzing trace levels of Cd in soils using graphite furnace atomic absorption spectrophotometry (GFAAS). None of these methods were found suitable for analyzing trace levels of Cd extracted by acidified ammonium oxalate [(NH₄)₂C₂O₄] 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 extracts encountering chemical interference especially from Fe. The recoveries of Cd were found to be 100±10% and the coefficient of variance was minimal.