Short Communication Electrochemical Reduction of Monochlorinated Hydrocarbons at a HydrophobicZn/PTFEComposite-ElectroplatedZnElectrodeina Water-AcetonitrileMixture Wisitsree Wiyaratn, a Mithran Somasundrum, b Werasak Surareungchai* a a School of Bioresources and Technology, King Mongkut×s University of Technology Thonburi, Bangkhuntien-Chaitalay Rd., Thakam, Bangkok 10150, Thailand *e-mail: werasak.sur@kmutt.ac.th b Biochemical Engineering and Pilot Plant Unit, National Center for Genetic Engineering and Biotechnology, Bangkhuntien- Chaitalay Rd., Thakam, Bangkok 10150, Thailand Received: July 11, 2002 Final version: October 24, 2002 Abstract Composite-electroplating of zinc particles with polytetrafluoroethylene at a zinc substrate resulted in a working electrode which could be used at high negative potentials (to  2.5 V vs. Ag/AgCl) without significant hydrogen evolution. The electrodes were characterized by SEM and CV and were used to detect organochloride compounds in a water-acetonitrile mixture, by potential step methods. Keywords: Chlorinated hydrocarbon, Electrochemical reduction, Composite zinc electrode Chlorinated hydrocarbons are used in various industries, such as textiles, and biocides for both agricultural and domestic use. Accidental or deliberate release of these materials into soil, watercourses, and the like can exert long- term toxic effects. Quantification of the problem requires a means of measuring their presence. Electrochemical detec- tion by reductive dechlorination has been performed using bacterial transition-metal coenzymes [1 ± 2], vitamin B 12 [2], coenzyme F430 [1 ± 2] and hetamin [3 ± 4]. However, retention of immobilized mediator may be a limit to stability. A simpler method is to detect organohalides by direct reduction at metal electrodes such as Hg, Pb, Pt, or Zn at typically between  1.3 and  2.4 V (vs. SCE) [5 ± 8]. However, in this potential range hydrogen evolution occurs, which makes the organohalide reaction inefficient, due to the formation of bubbles on the electrode surface. The use of electroplated metal/hydrophobic polymer composites has been researched for either the reduction or oxidation of a variety of organic compounds [9 ± 12]. Composite-plating has been found to provide stable films. Because of their strongly hydrophobic nature, these films are able to suppress oxygen and hydrogen evolution in aqueous solutions, and consequently increase the current efficiencies of compounds reacting at these potentials. Reports of composite-plated electrodes have focused on either organic synthesis or pollutant degredation. The analytical utility of such films has not so far been examined. Hence, this is the objective of this work. A composite of electroplated zinc particles and PTFE was coated onto a Zn substrate, and applied to the electro- reduction of monochlorinated organohalide hydrocar- bons (mCHCs). A photomicrograph of the surface of a Zn/PTFE compo- site-plated zinc electrode is shown in Figure 1. The presence of Zn was indicated by EDS. The Zn deposits were identified by their granular texture and well-defined edges (where as a polymer is expected to appear amorphous), and appeared both as reticular columnar grains (white particles) and globular grains, labelled as a and b, respectively, in Figure 1. PTFE appeared as agglomerate dispersions, intercalated in spaces between the crystalline grains of Zn. Adherent Fig. 1. Scanning electron micrograph of a Zn/PTFE composite- plated Zn electrode. The Zn deposits are present as reticular columnar grains (a) and globular grains (b). PTFE is present as agglomerate dispersions, intercalated in spaces between crystal- line Zn. 1719 Electroanalysis 2003, 15, No. 21 ¹ 2003 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim DOI: 10.1002/elan.200302748