Electrochemical detection of lead using overoxidized polypyrrole films Adam Wanekaya, Omowunmi A. Sadik  Department of Chemistry, State University of New York-Binghamton, P.O. Box 6016, Binghamton, NY 13902-6016, USA Received 11 June 2002; received in revised form 9 September 2002; accepted 11 October 2002 Abstract An electrochemical method for the determination of lead has been developed using overoxidized polypyrrole (OPPy) electrode doped with 2(2-pyridylazo)chromotropic acid anion (PACh 2 ). The PACh 2 acts both as a chelating agent and a counter anion within the polypyrrole matrix. In a typical assay, Pb 2 is accumulated on a solid electrode via the formation of a lead  /PACh complex at open circuit. The electrode containing the Pb 2 PACh 2 is then transferred to a 0.1 M acetate buffer where it is subjected to differential pulse anodic stripping voltammetry. The resulting stripping peak current was linearly related to the concentration of lead. The method has been optimized with respect to pH, concentration of chelating agent, accumulation time, reduction potential and time. The detection limit was found to be 10 ng ml 1 with a linear range of 0  /200 ng ml 1 . The method has been validated for the determination of lead using spiked potable water at 25 ng ml 1 . The average recovery was 93.4% with a relative standard deviation of 8.54%. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Accelerated solvent extraction; Pressure-assisted chelation; PACE; Digestion; Metals 1. Introduction Electrochemical methods enable the preparation of thin-films on electrodes that are subsequently used for the development of monitoring techniques for metal ions in the environment. In order to improve the selectivity of such techniques, the electrochemical mea- surements are carried out by first accumulating or preconcentrating the target metal from a dilute solution onto the electrode surface. This accumulation step can be performed with or without the use of applied potential. The latter approach called the open circuit enables the separation of the metal species under consideration thereby eliminating interferences [1] [2]. Electrically conducting polymers (ECPs) can act as a means of immobilizing metal  /ligand complexes on electrodes. ECPs can also be used to mediate redox transport between metal centers. We have used these characteristics to develop a method for monitoring Pb 2 . Electrodes modified with electrically conducting polypyrrole (PPy) containing complexing ligands have already been employed for the determination of various transition metals [1  /9] with such ligand-modified elec- trodes; accumulation involves only a chemical com- plexation reaction without any applied potential. Once the metal has been chemically accumulated from the sample solution onto the electrode, it can be transferred to a second metal-free solution for subsequent stripping analysis. This mode of medium exchange allows many potential interferants to be removed from the sample solution and can greatly improve the selectivity of the method. The feasibility of using electrodes modified with functionalized polymer films for electroanalysis of metal ions in solution was demonstrated by Guadalupe and Abruna [6]. Numerous ligands have been used for electroanalysis of metals and the factors affecting their electrochemical behavior extensively studied [1]. This include the electropolymerization and redox properties of bipyridyl-polypyrrole and Cu(II) bipyridyl-polypyr- role film electrodes [7], the electrochemistry and electro- nic conductivities of conducting polymers containing  Corresponding author. Fax:  /1-607-777-4132 E-mail address: osadik@binghamton.edu (O.A. Sadik). Journal of Electroanalytical Chemistry 537 (2002) 135  /143 www.elsevier.com/locate/jelechem 0022-0728/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0728(02)01261-5