Analytical Sciences

A Rapid Spectrophotometric Method for the Determination of Trace Level Lead Using 1,5-Diphenylthiocarbazone in Aqueous Micellar Solutions

Humaira KHAN, M. Jamaluddin AHMED, and M. Iqbal BHANGER

National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan

A very simple, ultra-sensitive and fairly selective direct spectrophotmetric method is presented for the rapid determination of lead(II) at ultra-trace level using 1,5-diphenylthiocarbazone (dithizone) in micellar media. The presence of the micellar system avoids the previous steps of solvent extraction and reduces the cost and toxicity while enhancing the sensitivity, selectivity and the molar absorptivity. The molar absorptivities of the lead-dithizone complex formed in the presence of the cationic cetyltrimethylammonium bromide (CTAB) surfactants are almost ten times the value observed in the standard method, resulting in an increase in the sensitivity of the method. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption coefficient was found to be 3.99 × 10⁵ L mol^-1 cm^-1 and Sandell's sensitivity was 30 ng cm^-2 of Pb. Linear calibration graphs were obtained for 0.06 - 60 mg L^-1 of Pb(II); the stoichiometric composition of the chelate is 1:2 (Pb:dithizone). The interference from over 50 cations, anions and complexing agents has been studied at 1 mg L^-1 of Pb(II). The method was successfully used in the determination of lead in several standard reference materials (alloys and steels), environmental water samples (potable and polluted), biological samples (human blood and urine), soil samples and solutions containing both lead(II) and lead(IV) and complex synthetic mixtures. The method has high precision and accuracy (σ = ±0.01 for 0.5 mg L^-1).

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