Copper-selective PVC membrane electrodes based on salens as carriers

Copper(II) selective sensors have been fabricated from polyvinyl chloride (PVC) matrix membranes containing carriers, 2,2′-[1,2-ethandiyl-bis(nitrilomethylidine)-bis]meta cresole(I),2,2′-[1,2-ethandiyl-bis(nitrilomethylidine)-bis]para cresole(II) and 2,2′-[1,2-ethandiyl-bis(nitrilomethylidine)-bis]ortho cresole(III) as ionophores, dibutyl phthalate (DBP), benzyl acetate (BA), acetophenone (AP) and o-nitrophenyl octyl ether (NPOE) as plasticizing solvent mediators and sodium tetraphenylborate (STPB) and oleic acid (OA) as additives. Best performance was exhibited by the membrane having a composition ionophore (SALEN):PVC:NPOE:OA in the ratio of 4:31:55:10 (w/w). These membranes give a linear potential response in the concentration range (1.0×10−5 to 1.0×10−1 M) with a Nernstian slope of 29.2±0.3, 29.7±0.3 and 28.2±0.3 mV/decade of Cu2+ and limits of detection are 3.6×10−6 M, 3.1×10−6 M and 6.3×10−6 M for salen (I), (II) and (III), respectively. It has a very short response time, less than 10 s, and can be used for at least 9 weeks without any divergence in potential. The copper (II) selective electrode exhibited very good selectivities with respect to alkali, alkali earth and some transition metal ions and could be used in a pH range 3.5-6.5. It was successfully applied for the direct determination of copper in sample of brass and a sample of Wilson's patient's urine. This electrode was also used as an indicator electrode in titration of Cu2+ with EDTA.