Abstract: The oxidation of Irganox 1076 (I-1076) at a glassy carbon electrode in aqueous 60% ethanol was studied by various voltammetric techniques. Based on the results a differential pulse voltammetric method was developed for the determination of I-1076 in commercial PVC-based plastics. The plastic was extracted with acetonitrile overnight, the extract was evaporated to dryness under N2 and the residue was dissolved in ethanol. The solution was diluted with water after the addition of 1 M acetic acid/acetate buffer at pH 4.5. The differential pulse voltammogram was recorded from 0-0.8 V with a scan rate of 10 mV/s and a pulse amplitude of 50 mV using a glassy carbon disc electrode with a SCE reference electrode and a Pt wire counter electrode. The calibration graph was linear for 1-25 µM-I-1076 with a detection limit of 0.23 µM. The RSD for 10 µM-I-1076 was 3.3.%. A FIA method with pulsed amperometric detection was also developed for I-1076 in PVC. The system used a wall-jet detector cell with a glassy carbon electrode, a Ag/AgCl/3 M KCl reference electrode and a Au counter electrode. Sample solution was injected into an acetic acid/acetate buffer carrier stream (2.8 ml/min, pH 4.5) and the pulse amperometric detector was operated with a measuring potential of 0.7 V for 0.1 s and a cleaning potential of -1 V for 0.2 s. Calibration graphs were linear for 0.2-1 µM and 1-10 µM with detection limits of 0.08 µM. The RSD (n = 12) for 5 µM-I-1076 was 2.3%.

Abstract: The voltammetric and flow injection amperometric behaviors of several substances used as antioxidants in the food and pharmaceutical industries at carbon paste electrodes, with paraffin as binding agent, and at graphite-40% PTFE composite electrodes were compared on the basis of the different hydrophobicity of the antioxidants. Aqueous solutions, alcohol-water mixtures and oil-in-water-emulsions were used as working media. No voltammetric or flow injection responses were obtained for high hydrophobic antioxidants (BHT, Irganox-1076 and Irganox-1010) at graphite-PTFE electrodes. On the contrary, carbon paste electrodes allowed the attainment of analytically useful signals for these compounds. A pulse amperometric detection (PAD) scheme should be applied in these cases for the cleaning of the electrode surface. The use of graphite-PTFE electrodes seems to be advantageous for the less hydrophobic antioxidants such us propyl gallate and TBHQ. An adsorption process for PG and a faster electrode kinetic in the case of TBHQ were shown to occur by cyclic voltammetry at the PTFE composite electrode. Furthermore, this electrode allows the use of lower potentials for the amperometric detection of these compounds than the carbon paste electrode. Good reproducibility of the successive amperometric responses was also observed. The mutual influence of the electrode surface composition and the lipophilic characteristics of the molecules tested is discussed.