Column solid-phase extraction with 2-acetylmercaptophenyldiazoaminoazobenzene (AMPDAA) impregnated amberlite XAD-4 and determination of trace heavy metals in natural waters by flame atomic absorption spectrometry

A column solid-phase extraction (SPE) preconcentration method was developed for the determination of Cd, Co, Cu, Ni and Zn ions in natural water samples by flame atomic absorption spectrometry. The procedure is based on the retention of analytes in the form of 2-acetylmercaptophenyldiazoaminoazobenzene (AMPDAA) complexes on a short column of AMPDAA-XAD-4 resin from buffered sample solution and subsequent elution with hydrochloric acid plus sodium chloride. Important SPE parameters were optimized using model solutions. The loading half-time, t(1/2), for Cd, Co, Cu and Zn was found to be less than 5 min, and for Ni the value was 12 min. The detection limit for Cd, Co, Cu, Ni and Zn was 0.028, 0.064, 0.042, 0.023 and 0.16 mug L-1, respectively, and the quantification limit was 0.043, 0.11, 0.099, 0.044 and 0.29 mug L-1, respectively. The AMPDAA-XAD-4 resin has good selectivity for Cd, Co, Cu, Ni and Zn over several electrolytes, especially over earth alkaline metals with tolerance limits of 0.05 mol L-1. The method was validated by analysing a standard reference material (GBW 08301), and it was found that the results agree with those quoted by the manufactures. The developed method was applied to the determination of trace metal ions in tap water and river water samples with satisfactory results.