Laser-Induced Graphene\nfor Electrochemical Sensing\nof Antioxidants in Biodiesel

Synthetic antioxidants are often introduced to biodiesel\nto increase\nits oxidative stability, and <i>tert</i>-butyl hydroquinone\n(TBHQ) has been selected due to its high efficiency for this purpose.\nThe monitoring of antioxidants in biodiesel therefore provides information\non the oxidative stability of biodiesels. Herein, a laser-induced\ngraphene (LIG) electrode is introduced as a new sensor for detecting <i>tert</i>-butyl hydroquinone (TBHQ) in biodiesel samples. An\ninfrared CO<sub>2</sub> laser was applied for LIG formation from the\npyrolysis of polyimide (Kapton). Based on the voltammetric profile\nof a reversible redox probe, the fabrication of LIG electrodes was\nset using 1.0 W power and 40 mm s<sup>–1</sup> speed, which\npresented an electroactive area of 0.26 cm<sup>2</sup> (higher than\nthe geometric area of 0.196 cm<sup>2</sup>). Importantly, lower engraving\nspeed resulted in higher electroactive area, probably due to a more\nefficient graphene formation. Scanning-electron microscopy and Raman\nspectroscopy confirmed the creation of porous graphene induced by\nlaser. The sensing platform enabled the differential-pulse voltammetric\ndetermination of TBHQ from 5 and 450 μmol L<sup>–1</sup>. The values of detection limit (LOD) of 2 μmol L<sup>–1</sup> and RSD (relative standard deviation) of 2.5% (<i>n</i> = 10, 10 μmol L<sup>–1</sup> of TBHQ) were obtained.\nThe analysis of spiked biodiesel samples revealed recoveries from\n88 to 106%. Also, the method provides a satisfactory selectivity,\nas it is free of interference from metallic ions (Fe<sup>3+</sup>,\nMn<sup>2+</sup>, Cr<sup>2+</sup>, Zn<sup>2+</sup>, Pb<sup>2+</sup>, and Cu<sup>2+</sup>) commonly presented in the biofuel. These results\nshow that LIG electrodes can be a new electroanalytical tool for detecting\nand quantifying TBHQ in biodiesel.