Fabrication and Characterization of a PVC Membrane Ni (II)-Selective Sensor Using 3-Hydroxy-4-[(2-Hydroxyphenyl) amino] cyclobut-3-ene-1,2-dione as a Neutral Carrier

A poly (vinyl chloride) (PVC)-based ion-selective membrane electrode was successfully fabricated for the selective detection of nickel (II) ions by employing 3-hydroxy-4-(2-hydroxyphenylamino) cyclobut-3-ene-1,2-dione (L) as the ionophore. The membrane formulation included sodium tetraphenylborate (NaTPB) as a lipophilic anionic additive to enhance ion-exchange characteristics and tris-(2-ethylhexyl) phosphate (TEHP) as the plasticizer. Among the different membrane formulations investigated, the composition containing L: NaTPB: TEHP: PVC in a weight ratio of 10:1:100:200 exhibited the best analytical performance. The optimized membrane electrode produced a linear potentiometric response toward Ni²⁺ over the concentration range of 2.1 × 10⁻⁸ to 1.0 × 10⁻¹ M, with a detection limit of 1.3 × 10⁻⁹ M. It showed a near-Nernstian sensitivity of 29.1 mV per decade change in nickel ion activity. Reliable and stable potential measurements were obtained within the pH range of 2.0–10.0, while the electrode reached equilibrium within approximately 8 s, indicating a rapid response. The sensor also maintained satisfactory performance in mixed solvent systems containing up to 30% (v/v) non-aqueous media and retained its sensing characteristics for nearly four months without significant deterioration. In addition, the membrane demonstrated excellent selectivity for Ni²⁺ over a wide range of interfering mono-, di-, and trivalent metal ions. The practical utility of the developed electrode was further demonstrated by its successful application as an indicator electrode during potentiometric titration of nickel (II) with EDTA and for the quantitative determination of nickel ions in real samples.