Development of an optode based on 2-amino-4-(4-nitrophenyl)diazenyl pyridine-3-ol and tri-n-octyl phosphine oxide for trace-level lead detection in complex samples†

Abstract

A new selective optode has been created for the ultra-sensitive detection of lead ions at trace levels. The membrane is created by incorporating tri-n-octylphosphine oxide (TOPO), 2-amino-4-(4-nitrophenyl)diazenyl pyridine-3-ol (ANPDP), and sodium tetraphenylborate (Na-TPB) into a matrix of plasticized poly(vinyl chloride) (PVC) and o-nitrophenyloctyl ether (o-NPOE). ANPDP serves as a chromophore in this design, while TOPO promotes the formation of a complex between lead ions (Pb²⁺) and ANPDP, resulting in a cooperative interaction. The composition of the optode was optimized to achieve maximum sensor performance. The sensor exhibits a linear dynamic range from 6.0 to 160 ng mL⁻¹, with quantification and detection limits of 5.9 ng mL⁻¹ and 1.8 ng mL⁻¹, respectively. The membrane demonstrated rapid response times and long-term durability, with no detectable leaching of ANPDP. To ensure accurate total lead determination, Pb⁴⁺ ions were reduced to Pb²⁺ using 6.00 M HCl and freshly prepared 2.50% (w/v) sodium azide. The optode sensor exhibited superior specificity for Pb²⁺ ions, even when other ions that could potentially interfere were present. It could be effectively regenerated by treatment with 0.1 M ethylenedi-aminetetraacetic acid (EDTA), restoring its functionality for repeated use. The sensor was successfully applied to detect lead in various complex matrices, including biological fluids, environmental water, and food samples, demonstrating its broad applicability and reliability for real-world lead monitoring.