Synthesis of a New Octadentates Schiff's Base and Its Application in Construction of a Highly Selective and Sensitive Lanthanum (III) Membrane Sensor

In this study, a new poly(vinyl chloride) (PVC) membrane sensor for La³⁺ ion based on bis(5-nitro-2-furaldehyde)butane-2,3-dihydrazone (BNFB) (octadentates Schiff's base) as an ion carrier was prepared. The sensor displays high selectivity for lanthanum with respect to many common alkali, alkaline earth, transition and heavy metal ions. The sensor revealed a great enhancement in selectivity coefficients for La(III), in comparison with the previously reported Lanthanum electrodes. The effect of membrane composition and pH on the response properties of electrode was investigated. The sensor with membrane composition of 30% PVC, 56% benzyl acetate as a solvent mediator, 8% (0.022 mmol) ionophore BNFB and 6% (0.021 mmol) oleic acid as an anionic additive, shows the best potentiometric response characteristics. It displays a Nernstian behavior (19.8 ± 0.2 mV per decade) over the concentration range of 1.0 × 10⁻⁷–1.0 × 10⁻¹ M. The detection limit of the electrode is 4.0 × 10⁻⁸M (5.6 ng/ml). The response time of the electrode is very fast (∼20 s) in whole concentration range. The sensor can be used in the pH range of 4.0–7.5 for at least two months. The membrane sensor was used as an indicator electrode in potentiometric titration of lanthanum ions with EDTA. It was successfully applied in determination of fluoride ions in mouth wash preparations.