DETERMINAÇÃO ANALÍTICA DE CONTAMINANTES AMBIENTAIS UTILIZANDO DISPOSITIVO MICROFLUÍDICO E TÉCNICAS DE DETECÇÃO ELETROQUÍMICAS

Abstract

This dissertation describes the construction (prototyping, assembly and use) of a microfluidic thread-electrochemical device (μTED) based on cotton threads and fully 3D-printed, whose structure is divided in an electrochemical detector composed of conductive carbon black/polylactic acid CB/PLA filament integrated to an acrylonitrile butadiene styrene (ABS) structure. This device was first used for the amperometric detection of nitrite. In addition, for the first time, an electroanalytical study using pencil graphite electrodes (PGEs) and square wave voltammetry (SWV) for electrochemical detection of fungicide benzovindiflupyr (BZN) is presented. The work is divided into three chapters: Chapter 1 brings a bibliographical review to contextualize the subjects that were covered throughout the work; Chapter 2 presents a new methodology and the development of a 3D-printed microfluidic device as a promising alternative for flow analysis that has been employed for the electrochemical detection of nitrite. Presenting low production cost, reduced consumption of reagents and minimal waste generation, in addition to providing portability and speed of analysis, this device was entirely manufactured using a 3D printer and has cotton threads as microfluidic channels. 3D-printed CB/PLA electrodes were used as electrochemical sensors for amperometric detection. The electrochemical behavior of nitrite was evaluated and the experimental parameters were optimized. A flow rate of 0.41 μL s-1 was achieved. A detection of limit (LOD) of 2.38 μmol L-1, a limit of quantification (LOQ) of 7.94 μmol L-1 and high precision (RSD of 2.1 %) were achieved by the developed method. The proposed device was, for the first time, applied for the determination of nitrite in water samples. It presented satisfactory results (recoveries of approximately 104 %) and demonstrated potential to extend the use of microfluidic devices which, based on their simplicity and good analytical performance, may overcome some limitations of conventional flow analysis systems; Chapter 3 presents the development of a new electroanalytical method for analysis of benzovindiflupyr employing pencil graphite electrodes as electrochemical sensors. The behavior and electro-oxidation processes of BZN were studied using cyclic voltammetry in 0.1 mol L-1 BR buffer at different pH values (1.0 to 4.5). The pH value of 4.0 was selected as ideal and the voltammetric technique chosen and optimized was the SWV, whose best parameters were: 4 mV potential increment, 45 Hz frequency, 30 mV amplitude, +0.45 V deposition potential and 30s deposition time. Under the optimized conditions, a dynamic linear range was observed (1.25 to 12.5 μmol L-1) with R2 of 0.999. The LOD and LOQ values obtained were 0.29 μmol L-1 and 0.99 μmol L-1, respectively. Repeatability, reproducibility and stability were satisfactory with RSDs of 2.4 %, 3.7 % and 7.5 %, respectively. The real analysis of commercial formulations by external standard showed recoveries below 104 % and RSD below 3.2 %. The data presented here are the first reported in literature that demonstrate an electroanalytical study and the development of a method for the electrochemical detection of BZN in commercial samples of fungicides, bringing a new alternative to the analysis of pesticides.