Highly selective dibenzo-18-crown-6-based optical sensor for pico-molar determination of Pb²⁺ for sustainable human...

A novel highly sensitive bulk PVC-membrane optode was developed for the selective determination of Pb²⁺. The optimized bulk optode incorporated 0.0038 g dibenzo-18-crown-6 ionophore, 0.0009 g sodium tetrakis 3,5-bis(trifluorophenyl methyl) borate ion-exchanger, and 0.0014 g ETH 5294 chromoionophore, all were dissolved in tetrahydrofuran (THF) slurry of 0.030 g poly-vinyl chloride (PVC) and 0.060 g ortho-nitrophenyl octyl ether plasticizer. The as-prepared bulk optode exhibited neutral carrier mechanism in a linear concentration range of 10^-12 - 10^-8 M, with a detection limit of 1.0 × 10^-12 M; acetate buffer of pH 5.0 was used through this work, and the response time was less than 2 min. The response mechanism was elucidated; it was found that complexation takes place between the oxygens of dibenzo-18-crown-6 ionophore and Pb²⁺ analyte via coordination with the high electron density open ether cavity in 1:1 ratio, as confirmed by FTIR, UV-Visible spectroscopy, and Molar ratio method. The high selectivity of dibenzo-18-crown-6 ionophore was confirmed for Pb²⁺ over the interfering ions including Ag⁺, K⁺, NH₄⁺, Cd²⁺, Ni²⁺, Co²⁺, Na⁺, Mg²⁺, Mn²⁺, Cl^-, SO₄^2-, CO₃^2-, and acetate anion; selectivity was confirmed by UV-Visible measurements, that exhibited maximum shift in case of Pb²⁺. The optode was applied successfully in biological samples of spiked urine solutions, and environmental samples of spiked industrial solutions; it exhibited recovery and standard deviation results of 97-108 % and < 1.1, respectively, which confirm the accuracy precision of the proposed method. Although the ionophore was applied before in ion selective electrodes, but this is the first application in bulk optode media, which facilitates the determination of Pb²⁺ over extended concentration range, with very high sensitivity and very high selectivity, due to Pb²⁺-dibenzo-18-crown-6 host-guest complexation in optode phase.