Simultaneous Voltammetric Determination of tert-Butylhydroquinone and Propyl Gallate in Biodiesel–Ethanol at a Pt Ultramicroelectrode

A direct non-aqueous method for simultaneous determination of propyl gallate (PG) and tert-butylhydroquinone (TBHQ) in biodiesel (B100) is described. Differential pulse voltammetry (DPV) using a Pt disk ultramicroelectrode (ume) in 1:1 (v/v) B100/ethanol containing 0.02 mol L–1 tetrahexylammonium perchlorate showed two oxidation peaks in the range from 1.20 × 10–3 to 8.9 × 10–3 mol L–1 for TBHQ and from 8.6 × 10–4 to 4.9 × 10–3 mol L–1 for PG. Simultaneous quantification and addition–recovery experiments were carried out in antioxidant-free B100 samples spiked with variable concentrations of TBHQ and PG. Because of significant overlapping in oxidation signals, the amount of TBHQ and PG in B100 was calculated through calibration graphs after voltammogram deconvolution using Microcal Origin software (version 8.0). The method provides a direct, low-cost, non-aqueous, and small volume procedure for simultaneous quantification of TBHQ and PG in B100, with 116 and 104% recovery values, respectively.