A PVC-based capric acid membrane potentiometric sensor for lead(II) ions M.F. Mousavi * , M.B. Barzegar, S. Sahari Department of Chemistry, Tarbiat Modarres University, P.O. Box 14115-111, Tehran, Iran Received 17 February 2000; received in revised form 11 September 2000; accepted 20 November 2000 Abstract Four different fatty acids (C7, C10, C14, and C18) were studied to characterize their abilities as lead(II) ion carrier in PVC membrane electrodes. The electrode based on capric acid [CH 3 (CH 2 ) 8 COOH] shows good Nernestian response for Pb 2 ions. The optimum composition of the membrane was 30 wt.% poly(vinyl chloride), 60 wt.% NPOE as plasticizer, 5 wt.% ionophore, and 5 wt.% potassium tetrakis (p-chlorophenyl) borate as lipophilic salt. The electrode exhibits a Nernstian slope of 29:0  0:5 mV per decade for Pb 2 over a wide concentration range (1:0  10 5 1:0  10 2 ). It can be used for a period of 3 months without any considerable divergence in potentials. The proposed electrode revealed good selectivities for Pb 2 over a wide variety of other metal ions and could be used in the pH range of 4.5±7. It shows a good stability, good reproducibility, and fast response. The electrode was used for the potentiometric titration of chromate ions with lead ions. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Lead; Ion-selective electrode; Capric acid ionophore; PVC membrane; Potentiometry; Fatty acid 1. Introduction Because of the importance of developing new ionophores in construction of liquid/polymer membrane-type ion-selec- tive electrodes, many cyclic and acyclic macromolecules have been introduced as ionophores. From these series, crown ethers [1±3], polyamines [4], calixarenes [5], metal- loporphyrines [6], RNA [7], metallocenes [8], Lewis acid containing receptors such as tin, silicon, boron, and mercury [9,10] have been shown to bind some organic and inorganic cations and anions reversibly and selectively, but need to introducing an easily available, cheap and suitable iono- phore is of much more interest. Heavy metals such as lead, mercury, and cadmium are toxic when absorbed in the body. Their accumulative beha- vior causes poisoning, cancer, brain damage, etc. [11]. Lead is a general metabolic poison and enzyme inhibitor. It can cause mental retardation and semipermanent brain damage in young children. Lead has the ability to replace calcium in bone to form sites for long-term release [11]. Because of the increased industrial use of lead, on one hand, and its serious hazardous effect to human health, on the other hand, the electrochemical properties and preparation of the lead ion- selective membrane electrodes have been extensively stu- died by using different active materials [12±21]. Recently, sodium caprate has been used as a scavenger for lead from waste water [22]. In this work, we report PVC membrane electrodes based on some organic acids which exhibit signi®cantly high selectivity to Pb 2 ions over alkali, alkaline earth and several transition metal ions. 2. Experimental 2.1. Reagents All reagents used were of analytical grade. Doubly dis- tilled water was used for preparing all aqueous solutions. High molecular weight poly(vinyl chloride) powder (PVC) was obtained from Fluka. Dibuthylsebecate (DBS), 2-nitro- phenyl octyl ether (NPOE), 2-nitrophenyl pentyl ether (NPPE), capric acid (C10), potassium tetrakis (p-chlorophe- nyl) borate (KTpClPB), sodium tetraphenyl borate (TPB), and tetrahydrofuran (THF) were obtained from Fluka. Oenanthic acid (C7), myristic acid (C14), and stearic acid (C18) were obtained from Merck. The nitrate or chloride salts of the cations used (from Merck or Aldrich) were of the highest purity available and used without any further puri®cation. Sensors and Actuators B 73 (2001) 199±204 * Corresponding author. Fax: 98-21-8006544. E-mail address: mousavim@modares.ac.ir (M.F. Mousavi). 0925-4005/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0925-4005(00)00698-5