Ionophore Properties of Schiff Base Compounds as Ion Sensing Molecules for Fabricating Cu(II) Ion-Selective Electrodes

Bis(2-hydroxybenzaldehyde)-1,2-diaminoethane ( L I ), bis(2-hydroxybenzaldehyde)-1,3-diaminopropane ( L II ) and bis(2-hydroxybenzaldehyde)-4,4'-methylendianiline ( L III ) were examined as ionophores for fabrication of polyvinylchloride ( PVC ) membrane Cu(II) ion-selective potentiometric sensors. The optimum composition (%) for the sensors was: 5 L I , 30 PVC, 6 sodium tetraphenylborate ( NaTPB ), 59 ortho -nitrophenyloctyl ether ( NPOE ); 4 L II , 30 PVC, 5 NaTPB, 61 dibutyl phthalate; 6 L III , 30 PVC, 5 NaTPB, 59 NPOE. The linear response range of the electrodes was 5 × 10 –4 –0.05 (L I ), 5 × 10 –4 –0.1 (L II ) and 1 × 10 –6 –0.01 M (L III ), and the corresponding detection limits were 4 × 10 –4 , 4 × 10 –4 and 2 × 10 –7 M, respectively. The sensors were showed rapid response time (≈10 s). Their responses were independent on pH in the range 2.5–5.0 (L I ), 3.2–4.7 (L II ) and 4.0–5.0 (L III ). The selectivity of the prepared electrodes towards copper ions over some mono-, di- and trivalent metal ions was evaluated. The sensors were used as indicator electrode in potentiometric titration of copper ions in aqueous solutions.