Development of Screen Printed Electrodes Chemically Modified with Schiff Base Films for Application in Forensic Chemistry

Electrochemical techniques have often been used to analyze a broad range of substances of forensic importance. These techniques can offer certain operational advantages such as ease of automation, potential for field use and the capability of in vivo analysis. They can also furnish information about reaction mechanisms. Additionally, chemical modification of conventional electrode surface is commonly employed for increasing specificity or selectivity in drug analysis. In the case of cocaine, for example, a variety of modifiers have been used, including polymers, Schiff bases, and biological materials.

In this work, chemically modified screen printed electrodes (CM-SPE) using different Schiff base films were employed in the voltammetric investigation of cocaine, 3,4 - methylenedioxymethanphetamine (MDMA), and morphine. Dip coating process was chosen for the surface chemical modification. Three different electrode plateforms were employed: carbon, gold, and platinum.  with methanolic solution containing different Schiff base complexes with subsequent drying step at room temperature. 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 0.85V vs Ag/AgCl.

Voltammetric parameters such as E_prec, v, and t_prec were optimized in this study, being obtained the values of -0.80V (vs Ag/AgCl), 120 s, and 100 mV s^-1, respectively. The optimized amount of the chemical modifier was found to be 30 mg per electrode. Detection and quantification limits were obtained in 110 and 390 mmol L^-1, respectively. Additionally, intra and inter-day repeatability of 2.61% and 3.77%, were obtained for cocaine determination.  It was possible to obtain a transductor for cocaine in presence of morphine and MDMA with high specificity in trace levels.

The author acknowledges FAPESP (2013/17630-7) and CAPES (25/2014 Pro-Forenses) for financial suport.