Abstract

The voltammetric behavior of beta-carboline alkaloids at carbon nanotubes-modified glassy carbon electrodes, as well as their quantification by amperometric monitoring of the oxidation responses, are reported. Cyclic voltammograms of harmane, harmine, harmaline and harmalol at the CNT-GCE showed enhanced voltammetric responses with respect to those obtained at a bare GCE. The effect of pH on the oxidation i(p) and E-p values obtained by differential pulse voltammetry was discussed, as well as their mechanistic aspects. Hydrodynamic voltammogram of these compounds led us to select a potential value of +900 mV for their amperometric detection. Under these conditions, no fouling of the modified electrode surface is evidenced. The HPLC separation and determination of P-carboline alkaloids were carried out using a mobile phase consisting of 20% (v/v) methanol-20% (v/v) acetonitrile-0.05 mol L-1 HPO42- solution of pH 9.0. Detection limits ranging between 28 nM (harmalol) and 88 nM (harmaline) were achieved. The usefulness of the chromatographic method with amperometric detection at the CNT-GCE was demonstrated by analyzing soy seeds samples spiked with harmaline, harmane and harmine at a 0.25 mu g/g level.