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.