Sources of error in the determination of Cd and Pb in plant material by atomic absorption

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Abstract
Some difficulties were met when low levels of Cd and Pb were estimated in plant samples in this laboratory by atomic absorption spectrophotometry (AAS). A modified procedure, based on methyl isobutyl ketone (MIBK) extraction of the metal complexes with ammonium pyrollidine dithio carbamate (APDC), has been developed for use on samples digested with HNO3/HCIO4. The procedure was compared with X‐ray fluorescence and with other AAS methods including those based on dry ashing. Dry ashing gave generally lower values for Cd and Pb. Improvement in conditions of digestion and analysis are described. Of these, the presence of small amounts of Fe in standards and unknown samples increases the stability and reproducibility of absorbance values, especially for cadmium.