Novel fluorimetric bulk optode membrane based on 5,8-bis((5'-chloro-8'-hydroxy-7'-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane for selective detection of lead(II) ions.

A novel fluorescence chemical sensor for the highly sensitive and selective determination of Pb(2+) ions in aqueous solutions is described. The preliminary potentiometric and spectrofluorimetric complexation studies in solution revealed that the lipophilic ligand 5,8-bis((5'-chloro-8'-hydroxy-7'-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane (L2) forms a highly stable and selective PbL2 and Pb(L2)(2) complexes which results in a strong fluorescence quenching of the ligand. Thus, a novel fluorescence Pb(2+) sensing system was prepared by incorporating L2 as a neutral lead-selective fluoroionophore in the plasticized PVC membrane containing tetrakis(p-chlorophenyl) borate as a liphophilic anionic additive. The response of the sensor is based on the strong selective fluorescence quenching of L2 by Pb(2+) ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range of 3.0 x 10(-7) to 2.5x 10(-2)M with a relatively fast response time of less than 5 min. In addition to high stability, reversibility and reproducibility, the sensor shows a unique selectivity towards Pb(2+) ion with respect to common coexisting cations. The proposed fluorescence optode was successfully applied to the determination of lead in plastic toys and tap water samples.