PVC Based Selective Sensors for Ni²⁺ Ions Using Carboxylated and Methylated Porphine

Abstract: Poly vinylchloride (PVC) based membranes of 4,4',4'',4'''-21H,23H-porphine–5,10,15,20 –tetrayl) tetrakis (benzoic acid) (TBAP) and 2,3,7,8,12,13,17,18-octamethyl - 21H, 23H-porphine (OMP) were prepared using dibutyl phthalate (DBP), dioctylphthalate (DOP), dibutyl(butyl)phosphonate (DBBP) and 1-chloronaphthalene (CN) as plastcizing solvent mediators and sodium tetraphenylborate (NaTPB) as an anion excluder for Ni²⁺ selective sensors. TBAP based membrane exhibits linearity over a wide concentration range 2.0x10^-6–1.0x10^-1M (0.12 – 5.8x10³ppm) with a slope of 29.6 mV/decade of activity while OMP based membrane showed linear potential response in the concentration range 1.0x10^-5 –1.0x 10^-1M (0.60 – 5.8x10³ppm) with a Nernstian slope of 29.0 mV/decade of activity. The electrode assembly works between pH 2.0 – 7.0, exhibits a fast response time of 10-15s and performed satisfactorily over a period of six months with good reproducibility. Excellent selectivity of the order of 10^-3 over a number of cations and quantitative determination of Ni²⁺ in effluents discharged from electroplating industry demonstrates the utility of the proposed sensor. The electrode assembly was also used as an indicator electrode in the potentiometric titration of Ni²⁺ with EDTA.