Development of an analytical method for the determination of tert-butylhydroquinone in soybean biodiesel

In this paper we present a novel method for the analysis of the antioxidant tert-butylhydroquinone (TBHQ) in soybean biodiesel by differential pulse voltammetry (DPV) on a glassy carbon (GC) electrode. This method was developed by submitting biodiesel samples to liquid–liquid extraction using two different extraction solvents: acetonitrile (ACN) and ethanol (EtOH). The effects of type and volume of solvent, supporting electrolyte and pH were investigated and optimised. The parameters of the DPV technique were optimised and analytical curves were obtained by the standard addition method. Under optimum conditions, this method shows good linear response with correlation coefficient (r) values above 0.99. The limits of detection (LOD) and quantification (LOQ) were below 2.00 mg L−1. The percentages of recovery of TBHQ when added to biodiesel were 96.7–100.8% for both extraction solvents, with relative standard deviation (RSD) lower than 3%. This method was applied to commercial samples of soybean biodiesel containing 877.00 ppm TBHQ, with recovery of 110.1% and 99.4% achieved when ACN and EtOH were used as the extraction solvents, respectively. These results were similar to those obtained using high-performance liquid chromatography with ultraviolet detection (HPLC–UV), demonstrating the applicability of this method for the determination of TBHQ in soybean biodiesel samples.