Spectrophotometric determination of trace lead in water after preconcentration using mercaptosephadex

A highly sensitive and selective spectrophotometric method for determination of trace lead in water after pre-concentration using mercaptosephadex (MS-50) has been developed, the method based on the color reaction of lead(II) with dibromohydroxylphenylporphyrin. Under optimal condition, lead(II) reacts with the reagent to form a 1:2 yellow complex in presence of TritonX-100, which has a maximum absorption peak at 479 nm. The color reaction can complete rapidly and remain stable for 24 h in room temperature. The molar absorption coefficient of the lead complex, the limit of quantification, the limit of detection and relative standard deviations were found to be 2.35×105 l mol−1 cm−1, 4.3, 1.4 ng ml−1 and 1.0%, respectively. The absorbance of the lead complex at 479 nm is linear up to 0.48 μg ml−1 of lead(II). The effect of various co-existing ions in water were examined seriously. No interference was observed. Moreover, a simple pre-concentration method for trace lead in water was also studied using MS-50. It was found that trace lead in water can be adsorbed in 1.0 mol l−1 HCl and dissociated from MS-50 with 4.0 mol l−1 HCl quantitatively, that improves the selectivity and the sensitivity of method (its detection limit (3 s) changed into 0.2 ng ml−1 of lead) obviously. The proposed method has been applied to determine trace lead in water samples with satisfactory results.