Desenvolvimento de métodos eletroanalíticos utilizando sensor eletroquímico fabricado por impressão 3D para a determinação de antioxidantes em biocombustíveis

Abstract

Low oxidation stability is the main drawback of biodiesels and biokerosenes that is overcome by using antioxidants. These antioxidants (phenolic compounds) can be combined due to synergistic effects. This dissertation presents the potential demonstration that 3D printed electrochemical devices can be applied for electroanalysis of biofuels, including the monitoring of oxidation stability (one of the quality control parameters) by quantifying the antioxidant in biofuels. Working electrodes were manufactured using a 3D printer (a planar electrode) and a 3D pen (a cylindrical electrode), both manufactured with polymeric filament containing carbon black and acid polylactic (CB-PLA). The 3D pen was used to print the conductive part of the cylindrical electrode using the CB-PLA conductive filament on the printed cylindrical body, previously equipped with the copper wire. The cylindrical electrode was used in voltammetric experiments and the planar design was used in amperometric experiments. The electrochemical behavior of several antioxidant species was investigated, including tert-butyl-hydroquinone (TBHQ), butyl hydroxyanisole (BHA), 2,6-di-tert-butyl phenol (2,6-DTBP), pyrogallol (PY), catechol, hydroquinone, propyl gallate, octyl gallate, dopamine and galic acid on 3D printed CB-PLA electrode. Cyclic voltammetry experiments demonstrated that electrochemical treatment of the electrode surface in aqueous solution NaOH (0.5 mol L-1) is an important strategy to improve the electrochemical activity for oxidation of antioxidants. TBHQ, BHA, 2,6-DTBP and PY were selected for evaluation of the 3D printed sensor analytical performance. The simultaneous voltammetric determination of TBHQ and BHA in biodiesel by differential-pulse voltammetry resulted in linear responses in the range of 0.5 and 175 µmol L-1 with limits of detection of 0.21 and 0.19 µmol L-1 for TBHQ and BHA, respectively. In addition, a fast and simple method using batch-injection analysis with amperometric detection (BIA-AD) for PY determination has been developed, which showed adequate detectability (LOD = 0.20 µmol L-1) and wide linear range (0.5 to 300 µmol L-1). The determination of 2,6-DTBP in biokerosene was achieved by cyclic voltammetry. All relative standard deviations (inter-electrode and inter-day) were lower than 6.0 %, indicating adequate precision. The recovery values for applications in biodiesel and biokerosene samples range from 82 to 119 %, testing to absence of matrix effect and good accuracy. In general, the proposed methods are easy, fast and with adequate portability aiming at field applications in the quality control of biofuels.

Keywords: 3D printing; antioxidants; carbon black/polylactic acid; biodiesel; biokerosene, differential pulse voltammetry; batch-injection analysis.