Ni(II) selective sensors based on Schiff bases membranes in poly(vinyl chloride)

The two nickel chelates of Schiff bases, 3-hydroxy-N-{2-[(3-hydroxy-N-phenylbutyrimidoyl)-amino]-phenyl}-N′-phenylbutyramidine (M₁) and bis-4-(ethyliminomethyl)naphthalene-1-ol (M₂), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to nickel ion. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w; mg) of (M₁): PVC:NaTPB:CN in the ratio 5:150:5:150. The sensor shows a linear potential response for Ni²⁺ over a wide concentration range 1.6 × 10⁻⁷ to 1.0 × 10⁻² M with Nernstian compliance (30.0 ± 0.2 mV/decade of activity) within pH range 2.5-9.5 and a fast response time of 10 s. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol, and acetonitrile and could be used for a period of 4 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nickel in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.