An improved colorimetric determination of lead(II) in the presence of nonionic surfactant

Phenanthraquinone monophenyl thiosemicarbazone (PPT), an excellent color-forming chelating agent, combines to Pb(II) to form a slightly soluble complex in aqueous solution. To determine this metal ion, a tedious and time-consuming separation technique, such as liquid-liquid extraction, has to be performed. However, the Pb(II)-PPT complex could be determined conveniently by ultraviolet-visible (UV-Vis) spectrophotometry at 520 nm in a Tween 80 micellar medium that has polyoxyethylene groups. After conditions, such as the pH, the concentration of PPT and the stability, were adjusted to their optimum values, the sensitivities of the Pb(II) ions in the Tween 80 micellar medium and in chloroform were compared. It was shown that the sensitivity of Pb(II) in the Tween 80 micellar medium was higher than in chloroform. The interference from different cations and anions was studied. Beer's law was obeyed over a concentration range of 0-40 microg ml(-1). The detection limit of Pb(II) was 0.036 microg ml(-1). The recovery yields of the lead(II) in the synthetic mixtures and water samples ranged from 98 to 99.8%, and their relative standard deviations (RSD) were below 4%. The proposed method was successfully applied to the determination of lead in certified reference samples, biological samples and in environmental water samples.