O princípios da sustentabilidade aplicados no desenvolvimento de dispositivos eletroanalíticos miniaturizados para análises em microvolumes de amostras de bebidas

Abstract

The miniaturization of analytical devices is an ultimate trend in analytical chemistry since it directly contributes to reducing the side effects of chemical activities on the environment. Thus, in this study, we presented approaches to fabricate inexpensive and durable miniaturized electrochemical sensors by using the principles of sustainability such as: reducing, reusing, and recycling as guidelines The first device was produced by using the screen-printing technique with overhead projector sheets as the substrate and a conductive ink prepared by mixing graphite powder and colorless nail polish. The working electrode of these sensors was chemically modified with multi-walled carbon nanotubes (MWCNTs) and the effects of the acidic functionalization and the size of the MWCNTs on the analytical performance were evaluated. The sensor modified with the larger diameter acidic-functionalized MWCNTs was applied to determine caffeic acid in tea samples. The second device was based on micropipette tips and metallic wires recovered from a damaged combined glass electrode and a conductance cell. This device offered some advantages compared with other micropipette tip-based electrochemical devices: it is more robust and provided effective control of the working electrode potential. The analytical performance of this device was evaluated for TBHQ, ascorbic acid, hydrogen peroxide, and dopamine used as model analytes. The working electrode was modified with carbon nanotubes and the miniaturized device was used to determine the fungicide carbendazim in water and orange juice samples. Finally, the last proposed device was fabricated with an insulin syringe as the holder for the electrodes. A copper wire used in electrical home installations was used as the working electrode. A platinum plate, recovered from a broken conductance cell, and an Ag/AgCl wire, recovered from a damaged pH glass electrode, were used as the auxiliary and pseudo-reference electrode, respectively. The good analytical performance was ascribed to the low volume of the acceptor solution (500 μL) which allowed both the SO2 extraction and its preconcentration. The miniaturized device integrated with membraneless volatilization extraction enabled the development of a sensitive and selective analytical method to determine sulfite in beverage samples. Therefore, the approaches described to fabricate low-cost miniaturized electroanalytical devices are promising to perform electrochemical measurements in microvolumes and with portability capacity.