Voltammetric determination of lapachol in the presence of lapachones and in ethanolic extract of Tabebuia impetiginosa using an epoxy-graphite composite electrode

Abstract Square-wave anodic voltammetry (SWV) was used to determine lapachol using a laboratory-made graphite-epoxy electrode. The electrolytic medium consisted of an aqueous solution containing cationic surfactant CTAB (1.2 × 10 − 4  mol L − 1 ), buffer phosphate (4.0 × 10 − 2  mol L − 1 ; pH 6.0) and KNO 3 (1.0 mol L − 1 ). The cationic surfactant improved diffusion and interaction of the analyte with the electrode, producing a reversible process that improved the total current measured by SWV. Lapachol signal was measured at − 470 mV after pre-concentration at 400 mV during 140 s, using frequency of 30 Hz, pulse amplitude of 40 mV with step potential of 20 mV. The instrumental limit of detection was 0.029 mg L − 1 and the dynamic linear range covered two decades. In the presence of β-lapachone (structural isomer) selectivity was achieved by first order derivative of the SWV signal. Lapachol determination in ethanolic extract of heartwood of Tabebuia impetiginosa was accomplished after a simple thin-layer chromatographic separation of the analyte from components of the complex sample. The results agreed (at 95% confidence level) with the ones achieved by using high performance liquid chromatography with absorciometric detection.