ANALYTICAL APPLICATIONS OF CYLINDRICAL CARBON-FIBER MICROELECTRODES - SIMULTANEOUS VOLTAMMETRIC DETERMINATION OF PHENOLIC ANTIOXIDANTS IN FOOD

Cylindrical carbon fiber microelectrodes (CFMEs) (8 mu m in diameter and 8 mm in length) have been used to determine the phenolic antioxidants tert-butylhydroxyanisole (BHA) and tert-butylhydroxytoluene (BHT) in acetonitrile medium: The electrochemical behavior of the CFMEs was tested using ferrocene in pure acetonitrile. Pretreatment of the microelectrodes was not necessary for the voltammetric analysis of the antioxidants BHA and BHT. The influence of the supporting electrolyte concentration on i(p) and E(p) values obtained by differential pulse voltammetry (DPV) has been evaluated. Detection limits close to 70 mu g L(-1) of BHA or BHT were achieved. Square-wave voltammetry (SWV) of these antioxidants at the CFMEs showed current densities remarkably higher than those obtained at a conventional glassy carbon disk electrode. A background current various orders of magnitude lower was also observed at the CFME. An optimization of square-wave parameters was performed in order to achieve the best sensitivity and resolution of the net current responses. Linear calibration graphs were obtained in the concentration ranges (1.0-10.0) x 10(-5) and (1.0-10.0) x 10(-6) mol L(-1), their slopes being significantly higher than those obtained by DPV. Voltammograms from mixtures of BHA and BHT showed two well-defined oxidation peaks with a difference between peak potentials of similar to 300 mV, which allows the simultaneous determination of both antioxidants in this medium. Interferences from other substances commonly present in commercial antioxidant mixtures were tested. The developed method by SWV was applied to determine BHA and BHT in spiked samples of dehydrated potato flakes.