Analytical applications of poly(3-methylthiophene)-coated cylindrical carbon fiber microelectrodes

Some analytical applications of carbon fiber microelectrodes (CFMEs) modified with cyclic voltammetric electrogenerated poly(3-methylthiophene) (P3MT) coatings are described. Cyclic voltammograms in aqueous solutions of the phenolic antioxidants tert-butylhydroxyanisole (BHA), tert-butylhydroquinone (TBHQ), propylgallate (PG), and tert-butylhydroxytoluene (BHT) showed that electrocatalytic effects and an improved electrode kinetics occurred at the modified microelectrodes when compared with GC electrodes of conventional size. Moreover, reproducible voltammograms were obtained, obviating the need of cleaning or pretreatment of the coated microelectrode. Another important analytical advantage was the greatly improved resolution for mixtures of analytes. The behavior of P3MT-CFMEs in organized media was tested by considering their voltammetric response towards the electrochemical oxidation of PG. The nonionic surfactant Pluronic F 68 was selected as the most suitable to form micellar solutions of PG, as well as the emulsifying agent for the preparation of oil-in-water emulsions. A 20:80 ethyl acetate:n-hexane mixture was used as the organic phase and a 0.05 mol L-1 H3PO4/H2PO4- buffer solution of pH 2.0 as the aqueous continuous phase. Cyclic voltammetry demonstrated that the PG oxidation current was purely diffusion-controlled in the organized medium. The analytical characteristics obtained by using differential pulse voltammetry were slightly better than those obtained in aqueous solution. Furthermore, the improved resolution for mixtures of analytes is retained in the oil-in-water emulsified medium. The proposed method was applied with good results to the determination of PG in spiked commercial dehydrated soup samples by direct emulsification of aliquots of the sample extract in the ethyl acetate:n-hexane mixture.