Voltammetric behaviour of indole at carbon fibre microelectrodes in organic solvents: Application to the determination of indole in food samples

Abstract

The electroanalytical behaviour of indole at cylindrical carbon fibre microeleclrodes (CFMEs) in ethyl acetate containing tetrabulylammonium tetrafluoroborate (TBABF₄) as supporting electrolyte, has been reported. Voltammetry of indole is found to be dependent on the analyte concentration, which is attributed to a change in the electrooxidation mechanism at high concentrations. The repetitive cyclic voltammograms for a 2.5×10^-3 mol l^-1 concentration show oxidative electropolymerization of indole and subsequent deposition of the polymer film on the CFME surface. A square wave

voltammetric method for the determination of indole at low concentration levels in ethyl acetate is developed, with a linear range between 1.0×10^-6 and 6.0×10^-5 mol l^-1 and a limit of detection of 4.0×10^-7 mol l^-1. Unlike Pt eleclrodes, no appiication of cleaning pretreatment to the CFME surface is needed. Interferences from 3-methylindole, L –tryptophan, histidine, tryptamine and 3-methylamine have been checked, and also the possibility of using now-injection with amperometric detection have been evaluated. The voltammetric method at CFMEs, based on direct measurements of the analyte extract in ethylacetate, is applied to the determination of indole in spiked shrimps and pig back fat samples.