A new azo dye for colorimetric determination of lead(ii) ions

A new azo dye, S9b (1-amino-4-[(E)-2-(8-hydroxyquinolin-5-yl)diazen-1-yl]-9,10-dihydroanthracene-9,10-dione), was developed and evaluated as a colorimetric chemosensor for lead(ii) ions. Upon Pb²⁺ addition, the S9b solution color changed from rosy-brown to sandy-brown. The UV-vis spectrum of the S9b-Pb²⁺ complex exhibited a hyperchromic shift compared to free S9b and a bathochromic shift relative to S9b complexes with other metal ions. Optimized conditions comprised an ethanol solvent system, pH 6.0, a reaction time of 2 min, and a 2 : 1 molar ratio of S9b to Pb²⁺.The response of S9b was linear at Pb²⁺ concentrations of 3.90-9.36 μg mL^-1. The calculated detection limit, quantitation limit and binding constant were 1.55 μg mL^-1, 4.71 μg mL^-1 and 3.07 × 10⁴ L² g^-2, respectively. Determination of Pb²⁺ was not significantly affected by other interfering cations (Ag⁺, Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Na⁺, K⁺, Ni²⁺, Hg²⁺, Ca²⁺, Zn²⁺, Mg²⁺, and Al³⁺). The S9b-based method demonstrated recoveries of 100.03-103.11% and relative standard deviations (RSDs) of 0.06-2.07% for Pb²⁺ in spiked water samples, with accuracy and precision comparable to atomic absorption spectroscopy (AAS). FTIR studies and DFT calculations indicated that Pb²⁺ binding to S9b occurs via the heterocyclic nitrogen and phenolic hydroxyl groups of the azo dye. The sensor demonstrated reusability following regeneration with EDTA, which dissociated the Pb²⁺ complex. This study highlights the potential of the anthracene-9,10-dione-based azo dye as a simple, eco-friendly, and rapid chemosensor for Pb²⁺ detection in aqueous systems.