DOI: 10.1002/elan.201500372 Voltammetric Determination of Cocaine Using Carbon Screen Printed Electrodes Chemically Modified with Uranyl Schiff Base Films Maria Fernanda Muzetti Ribeiro, [a] JosØ Wilmo da Cruz Jfflnior, [a] Edward Ralph Dockal, [b] Bruce Royston McCord, [c] and Marcelo Firmino de Oliveira* [a] 1 Introduction 1.1 Narcotics Among the various compounds commonly used as narcot- ics, two species that are active in the central nervous system deserve special attention: marijuana, with D9- THC as the most important active ingredient in its com- position, and cocaine (as well as its free base, “crack”). These drugs account for 95 % of the casework related to drug trafficking in Brazil [1] and are common worldwide. Cocaine is the most important natural alkaloid extract- ed from the leaves of the coca bush Erythroxylon. In its purified hydrochloric form, this compound presents an ar- omatic odor, and consists of a white, crystalline, water- soluble solid that can be extracted or dissolved in water for intravenous administration. In addition, a new way of using cocaine is to mix the waste from cocaine production with sodium bicarbonate, to make the mixture alkaline. This generates the free-base form of cocaine, which com- prises a petrified mass, usually yellowish brown, popularly known as “crack”. The latter form is poorly soluble in water, but volatilizes easily upon heating (95 8C), so ad- dicts can smoke it in improvised pipes. The word “crack” derives from the characteristic noise the rocks make when broken down by smoking. The initial effects of co- caine on the body are euphoria, excitement, insomnia, and appetite suppression, because it acts on the central nervous system [2–4]. Abstract : Chemically modified screen printed electrodes (CM-SPE) using [UO 2 (4-MeOSalen)(H 2 O)]·H 2 O films were employed in the voltammetric determination of co- caine. The chemical modification was performed by dip coating electrode surfaces (carbon, gold, and platinum) with methanolic solution containing the Schiff base com- plex with subsequent drying step at room temperature. The optimized amount of the chemical modifier over the working electrode was found to be 2.39 mg mm 2 (geomet- ric area). The voltammetric measurements were carried out in 50 : 50 v/v methanol:water solution containing 0.05 mol L 1 KCl and 0.1 mol L 1 LiCl as a supporting electrolyte without oxygen elimination by inert gas flow. The best results were obtained with carbon electrodes. Cocaine exhibits a well defined irreversible anodic peak current (i pa ) at a potential (E pa ) of 0.85 V vs Ag/AgCl. The current is directly proportional to the drug concen- tration. An optimal accumulation potential (E prec ), and time (t prec ) of 0.80 V (vs Ag/AgCl), and 120 s, respectively, were de- termined. The linear dependence of i pa with square root of scan rate (u) indicates that the mass transport at the electrode surface is controlled by diffusion. An optimized scan rate of 100 mV s 1 was obtained for analytical pur- poses. A limit of detection (LOD) and limit of quantifica- tion (LOQ) in 110 and 390 mmol L 1 , respectively, with intra and inter-day repeatability of 2.61% and 3.77 %, re- spectively, were obtained. In interference studies the pro- posed method demonstrated high specificity for cocaine in the presence of morphine and 3,4-methylenedioxyme- thanphetamine. The above results demonstrate that this method provides a fast and low cost procedure for deter- mination of cocaine in trace levels. Keywords: voltammetry · forensic chemistry · cocaine · Schiff base · screen-printed electrode [a] M. F. Muzetti Ribeiro, J. W. da Cruz Jfflnior, M. F. de Oliveira Departamento de Química, Faculdade de Filosofia CiÞncias e Letras de Ribeir¼o Preto USP, 14040-901, Ribeir¼o Preto, SP, Brasil Tel. + 55-16-3602-3750, Fax. + 55-16-3602-4838 *e-mail: marcelex@usp.br [b] E. R. Dockal Departamento de Química, Centro de CiÞncias Exatas e de Tecnologia Universidade Federal de S¼o Carlos 13565-905 – S¼o Carlos, SP, Brasil [c] B. R. McCord Chemistry Department, International Forensic Research Institute Florida International University 33199 – Miami, FL – United States of America www.electroanalysis.wiley-vch.de # 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Electroanalysis 2016, 28, 320 – 326 320 Full Paper