No abstract

Potentiometric ion sensors based on polymeric membranes are well established and used in many laboratories; and sensors for about 60 analytes are currently known. 1 The increased industrial use of lead, and its serious effect on human health 2 have caused the electrochemical properties and preparation of the lead ion selective membrane electrodes to be extensively studied.During 1986 -1992, compounds such as dibenzo-18-crown-6 and diazadibenzo-18-crown-6 3 dibenzo-18-crown-6 and 3,17-diazadibenzo-18-crown-6 4 and monobenzo-15-crown-5 (MB15C5), MB15C5-tungstophosphoric acid and MB15C5-molybdophosphoric acid 5 were used as ionophores in lead ISEs. Later, lead in environmental samples was determined by an ISE by Li and Liu 6 . The pH of the medium was 4 and the Nernstian range was 1 × 10 -6 -1 × 10 -2 M with slope of 26.4 mV per decade.In 1999 Abbaspour and Tavakol 7 prepared a PVC leadselective electrode by using benzyl disulfide as an ionophore and dimethylsebacate (DMS) as a plasticizer. The linear range was 2 × 10 -5 -5 × 10 -2 M for Pb 2+ with a Nernstian slope of 29.2 ± 1.3 mV per decade.Also in 1999, lead selective membrane electrodes based on selected thiacrown ethers were prepared by Radacka et al. 8 In 2000, a PVC membrane electrode for Pb 2+ based on tetraphenylporphyrin was prepared by Shamsipur et al. 9 The linear range was 1.0 × 10 -5 -1.0 × 10 -2 M and the Nernstian slope was 30.0 mV/decade. In 2001, caprice acid was used for a PVC based lead selective electrode by Mousavi et al. 10 The electrode had a Nernstian slope of 29.0 ± 0.5 mV/decade for lead ions over a linear range of 1.0 × 10 -5 -1.0 × 10 -2 . The present lead-selective electrode is a PVC-based membrane using phenyl disulfide as ionophore and onitrophenyl octyl ether (NPOE) as a plasticizer. The proposed electrode shows a wide linear range and is applicable over a wide pH range. In this electrode, no additive such as sodium tetraphenylborate or potassium tetrakis (p-chlorophenyl) Experimental ReagentsReagent grade o-nitrophenyloctylether (NPOE) was obtained from Fluka; tetrahydrofuran (THF), dimethylsebacate (DMS), polyvinylcholoride (PVC), dibutylphetalate (DBP), benzyl acetate (BA) acetophenone (AP), and potassium tetrakis (pchlorophenyl) borate (KTpClPB) were all obtained from Merck Chemical Company. Phenyl disulfide was synthesized and used after purification according to the suggestion of described Firouzabadi et al. elsewhere. 11 Nitrate salts of all cations used (all from Merck) were of the highest purity available and were used without any further purification. All solutions were prepared from analytical reagents grade using triply distilled water and their measurements were performed in unbuffered solutions. Membrane preparationThe PVC membrane electrode was fabricated as in our previous works. 7,12,13 The membrane composition was 32.6 mg of PVC powder and 2.6 mg of phenyl disulfide as ionophore, with 64.8 mg of NPOE as solvent mediator. [14][15][16] Electrode system and EMF measurements All electromotive force (emf) meas...