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-hydroxyanisol e (BHA) and tert-butylhydroquinone (TBHQ), at a polymer electrode modified with nickel phthalocyanine as electron mediator, is described, and an elect roanalytical method for the determination of these antioxidants based on th eir 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 di sk electrode for both antioxidants. The peak currents measured at the modif ied 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 reduc tion product. This product is oxidised during the second cyclic scan, to ge nerate the mentioned TBHQ as final product. These studies also reveal that sensitive response for both antioxidants can be obtained by using the diffe rential pulse voltammetry (DPV) technique. Responses observed are dependent on the nature of the control solution (% methanol and pH) and the nature o f voltammetric conditions (potential amplitude, Delta E, and scan rate, ups ilon(b)). These factors have been modified in order to find the best analyt ical 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 wer e obtained. The detection limits were 2.1 ppm for both when CV was used, an d 18.7 ppm (BHA) and 1.23 ppm (TBHQ) for DPV. The developed methods were ap plied to the determination of BHA in spiked glaze biscuits and TBHQ in spik ed mushroom cream. (C) 1999 Elsevier Science B.V. All rights reserved.