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A methodology for direct and simultaneous determination of four phenolic antioxidantsbutylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PG), and tert-butylhydroquinone (TBHQ)in biodiesel samples using differential pulse voltammetry associated with partial least squares (PLS) regression is presented. Measurements were taken directly in a biodiesel:ethanol 1:1 (v/v) medium using a platinum ultramicroelectrode as the working electrode. The voltammetric signals of the compounds overlapped significantly, and to facilitate the simultaneous determination of the analytes, a PLS chemometric tool was applied and approaches fitting one compound at a time (PLS-1) and multiple compounds (PLS-2) both allowed the quantification of the individual concentrations, overcoming the strongly overlapped voltammograms. Results show that the PLS-2 model provides more accurate predictions than PLS-1. For the PLS-2 model, root mean square errors of prediction of 3 × 10, 16, 24, and 3 × 10 mg L–1 have been obtained between nominal and predicted concentrations for BHA, BHT, PG, and TBHQ, respectively. Recovery percentages were between 83 and 104%.

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.

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