Solid phase extraction of trace cadmium and lead in food samples using modified peanut shell prior to determination by flame atomic absorption spectrometry

Peanut shell was chemically modified with phosphoric acid and used as a solid phase extraction material for the determination of trace amounts of Pb2+ and Cd2+ in food samples by flame atomic absorption spectrometry. The effect of pH, sample flow rate and volume, elution flow rate and volume, and of potentially interfering ions on the recovery of the analytes were investigated. The results showed that Pb2+ and Cd2+ can be adsorbed at pH 6 and eluted with 1.5 mL of 0.1 mol L-1 HCl. Under the optimized conditions, the adsorption capacity of modified peanut shell was found to be 116.7 mg g(-1) and 37.5 mg g(-1) for Pb2+ and Cd2+, respectively. The limits of detection were as low as 2.3 and 0.2 ng mL(-1) for Pb2+ and Cd2+, respectively, with a theoretical concentration factor of 40. The analytical results for the certified reference tea sample (GBW07605) were in a good agreement with the certified value. The method has also been applied to the determination of trace Pb2+ and Cd2+ in tea, liquor and milk powder, and the recovery of Pb2+ and Cd2+ for spiked food samples was between 90 and 114%.