Voltammetric determination of the phenolic antioxidants 3-tert-butyl-4-hydroxyanisole and tert-butylhydroquinone at a polypyrrole electrode modified with a nickel phthalocyanine complex

The voltammetric behaviour of the antioxidants 3-tert-butyl-4-hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ), at a polymer electrode modified with nickel phthalocyanine as electron mediator, is described, and an electroanalytical method for the determination of these antioxidants based on their electrochemical oxidation on the modified electrode is proposed. Cyclic voltammograms showed well-defined oxidation peaks slightly shifted towards less positive potentials with respect to those obtained at the platinum disk electrode for both antioxidants. The peak currents measured at the modified electrode are considerably higher than those obtained at the unmodified electrode. A scan rate of 100 mV s(-1), a minimum methanol percentage of 0.5% and a 0.1-M Britton-Robinson medium were chosen as working conditions. The obtained results suggest that the BHA oxidation produces the TBHQ reduction product. This product is oxidised during the second cyclic scan, to generate the mentioned TBHQ as final product. These studies also reveal that sensitive response for both antioxidants can be obtained by using the differential pulse voltammetry (DPV) technique. Responses observed are dependent on the nature of the control solution (% methanol and pH) and the nature of voltammetric conditions (potential amplitude, Delta E, and scan rate, upsilon(b)). These factors have been modified in order to find the best analytical conditions. The mutual interferences between both antioxidants and the measurement reproducibility were tested. Using cyclic voltammetry (CV) and differential pulse voltammetry, BHA and TBHQ linear calibration graphs were obtained. The detection limits were 2.1 ppm for both when CV was used, and 18.7 ppm (BHA) and 1.23 ppm (TBHQ) for DPV. The developed methods were applied to the determination of BHA in spiked glaze biscuits and TBHQ in spiked mushroom cream. (C) 1999 Elsevier Science B.V. All rights reserved.