Spectrophotometric determination of lead in industrial, environmental, biological and soil samples using 2,5-dimercapto-1,3,4-thiadiazole

A very simple, ultra-sensitive and fairly selective non-extractive spectrophotometric method for the determination of trace amounts of lead with 2,5-dimercapto-1,3,4-thiadiazole (DMTD) has been developed. DMTD reacts in slightly acidic (0.0015–0.01 M HCl) aquatic media with lead(II) to give a greenish-yellow chelate, which has an absorption maximum at 375 nm. The reaction is instantaneous and absorbance remains stable for 24 h. The average molar absorption coefficient and Sandellʹs sensitivity were found to be 4.93×104 l mol−1 cm−1 and 15 ng cm−2 of Pb, respectively. Linear calibration graphs were obtained for 0.1–40 μg ml−1 of Pb; the stoichiometric composition of the chelate is 1:2 (Pb–DMTD). The interference from over 50 cations, anions and complexing agents has been studied at 1 μg ml−1 of Pb. The method developed was used successfully in the determination of lead in several standard reference materials (alloys and steels), environmental waters (potable and polluted), biological samples (human blood and urine), soil samples, solutions containing both lead(II) and lead(IV) and complex synthetic mixtures. The method has high precision and accuracy (S=±0.01 for 0.5 μg ml−1).