Laser-Induced Graphene for Electrochemical Sensing of Antioxidants in Biodiesel

Synthetic antioxidants are often introduced to biodiesel to increase its oxidative stability, and tert-butyl hydroquinone (TBHQ) has been selected due to its high efficiency for this purpose. The monitoring of antioxidants in biodiesel therefore provides information on the oxidative stability of biodiesels. Herein, a laser-induced graphene (LIG) electrode is introduced as a new sensor for detecting tert-butyl hydroquinone (TBHQ) in biodiesel samples. An infrared CO₂ laser was applied for LIG formation from the pyrolysis of polyimide (Kapton). Based on the voltammetric profile of a reversible redox probe, the fabrication of LIG electrodes was set using 1.0 W power and 40 mm s^-1 speed, which presented an electroactive area of 0.26 cm² (higher than the geometric area of 0.196 cm²). Importantly, lower engraving speed resulted in higher electroactive area, probably due to a more efficient graphene formation. Scanning-electron microscopy and Raman spectroscopy confirmed the creation of porous graphene induced by laser. The sensing platform enabled the differential-pulse voltammetric determination of TBHQ from 5 and 450 μmol L^-1. The values of detection limit (LOD) of 2 μmol L^-1 and RSD (relative standard deviation) of 2.5% (n = 10, 10 μmol L^-1 of TBHQ) were obtained. The analysis of spiked biodiesel samples revealed recoveries from 88 to 106%. Also, the method provides a satisfactory selectivity, as it is free of interference from metallic ions (Fe³⁺, Mn²⁺, Cr²⁺, Zn²⁺, Pb²⁺, and Cu²⁺) commonly presented in the biofuel. These results show that LIG electrodes can be a new electroanalytical tool for detecting and quantifying TBHQ in biodiesel.