Lead-Selective Poly(vinyl chloride) Membrane Electrode Bull. Korean Chem. Soc. 2005, Vol. 26, No. 1 51 Lead-Selective Poly(vinyl chloride) Membrane Electrode Based on 1-Phenyl-2-(2-quinolyl)-1,2-dioxo-2-(4-bromo) phenylhydrazone Hamid Reza Zare, * Mohammad Mazloum Ardakani, Navid Nasirizadeh, and Javad Safari † Department of Chemistry, Yazd University, Yazd 89195-741, Iran. * E-mail: hrzare@yazduni.ac.ir † Department of Chemistry, Kashan University, Kashan 51167, Iran Received July 19, 2004 A PVC membrane electrode for lead ion based on 1-phenyl-2-(2-quinolyl)-1,2-dioxo-2-(4-bromo) phenylhydrazone (PQDBP) as ionophore was demonstrated. The optimum composition of the membrane was 30 wt% poly(vinyl chloride), 60 wt% dibutyl phthalate as a plasticizer, 4 wt% ionophore and 6 wt% sodium tetraphenylborate as additive. The electrode exhibits a Nernstian response (28.7 mV decade -1 ) for Pb 2+ over a wide concentration range (1.0 × 10 -1 to 1 × 10 -6 M) with a detection limit of 6.0 × 10 -7 M. This sensor has a short response time and can be used for at least 2 months without any divergence in potentials. The proposed electrode could be used in a pH range of 3.0-6.0 and revealed good selectivities for Pb 2+ over a wide variety of other metal ions. It was successfully applied as an indicator electrode for the potentiometric titration of lead ion with potassium chromate and for the direct determination of lead in mine. Key Words : Lead ion-selective electrode, PVC membrane, Potentiometry Pb 2+ analysis, Neutral ionophore Introduction Over recent years, the importance of controlling the level of environmental pollutants in natural waterways, portable water and soils has generated increasing interest in the development of novel sensors for the detection of heavy metals. Potentiometric detectors based on ion-selective electrodes are suited, because they offer advantages such as high selectivity, sensitivity, good precision, simplicity and low cost. 1,2 These methods make possible direct monitoring of activities or concentrations of selected species without any sample pre-treatment. During the last two decades, a large number of neutral ionophores with high selectives for specific metal ions have been developed and have found widespread applications in potentiometric and optical sensors for the determination of the respective metal ions in a variety of real samples. 3,4 Because of the increased industrial use of lead and its serious hazardous effect to human health, 5 the electrochemical properties and prepa- ration of the lead ion selective membrane electrodes have been extensively studied by using different ligands as sensing agents in electrodes based on ionophore-doped poly(vinyl chloride) (PVC) membrane. 6-17 We have recently prepared a lead-selective membrane electrode based on cryptand (222) neutral carrier. 18 Also, we have used neutral ionophores, in the construction of PVC-membrane elect- rodes for Hg 2+ , 19 Ni 2+ , 20 and Ag + . 21 In this work, we report the use of 1-phenyl-2-(2-quinolyl)-1,2-dioxo-2-(4-bromo) phenylhydrazone (PQDBP) as an excellent neutral carrier in construction of a lead-PVC membrane electrode. Experimental Section Reagents and apparatus. Reagent grade dibutyl phtha- late (DBP), bis(2-ethylhexyl) phthalate (BEHP), sodium tetraphenylborate (NaTPB), oleic acid (OA), potassium chromate, tetrahydrofuran (THF) and the nitrate salts of all cations (all from Merck) were used as received. Poly(vinyl chloride) (PVC) of high relative molecular weight was purchased from Fluka. All other chemicals were of analytical reagent grade from either Merck or Fluka. pH adjustments were made with dilute nitric acid or sodium hydroxide. All solutions were prepared with doubly distilled deionized water. For preparation of real samples, 1.0 g of lead mineral was dissolved in nitric acid and the resulting solution appropriately diluted. All emf measurements were carried out with the following cell assembly: Ag/AgCl/3.0 M KCl/internal solution, 1.0 × 10 -2 M Pb(NO 3 ) 2 /PVC membrane/test solution/3.0 M KCl/AgCl/Ag A Metrohm ion analyzer pH/mV meter (model 691) was used for potential measurements at room temperature. The atomic absorption measurements were performed by the aid of a Buck Scientific Spectrometer (model VGP 210). Synthesis of ionophore. 1-Phenyl-2-(2-quinolyl)-1,2- dioxo-2-(4-bromo) phenylhydrazone (PQDBP) used as the ionophore was prepared as follows. An amount (0.860 g, 5 mmol) of 4-bromoaniline was dissolved in 15 mL 3.0 M hydrochloric acid in the presence of sodium nitrite. Then, a solution of 1-phenyl-2-quinolidene-2-yl-ethane-1-one (1.235 g, 5 mmol) in absolute ethanol (25 mL) was added and the mixture was stirred magnetically in 15 o C for 30 minutes. The resulting precipitate was filtered and recrystal- lized from absolute ethanol. After vacuum drying, the pure product of 1-phenyl-2-(2-quinolyl)-1,2-dioxo-2-(4-bromo) phenylhydrazone (PQDBP) (Fig. 1) was obtained as a yellow solid, yield 89%; m.p = 142 o C; IR (KBr, cm -1 ): 1595 (s), 1660 (m), 1616 (s); 1 H NMR (CDCl 3 , ppm): 7-8.7 (m, 10H, C 9 H 6 N+C 6 H 4 ), 16.52 (S, 1H, NH); MS, m/z 430.298 (M + ); Elemental Analysis, Calculated for C 23 H 16 N 3 OBr: C