Voltammetric Simultaneous Quantification of Lapachone Isomers In Plant Extracts Using Graphite–Epoxy Composite Electrode

Abstract

The method developed for the determination of lapachone isomers (α- and β-lapachones) involves the use of square wave voltammetry (SWV) with an electrode based on epoxy–graphite composite. The electrolytic aqueous solution contained a cationic surfactant (CTAB), phosphate buffer (pH 6.0), and KNO₃. The addition of CTAB enhanced analyte diffusion into the electrode–solution interface, improving detection through SWV. Under chosen conditions, β-lapachone and α-lapachone respectively present reversible and quasireversible processes. The analytical signals were detected at the specific potentials of −370 mV (α-lapachone) and −190 mV (β-lapachone) using 140 s preconcentration at +400 mV. The SWV parameters used include 30 Hz frequency, 40 mV pulse amplitude, and 20 mV potential step. Instrumental detection limits were 2.4 × 10⁻⁷ mol L⁻¹ and 1.4 × 10⁻⁷ mol L⁻¹ respectively for α-lapachone and β-lapachone. Lapachol and, in a lesser extent, sulfonated β-lapachone interfere with both analyte signals, requiring liquid–liquid extraction prior to the determination of α-lapachone and β-lapachone in ethanolic plant (heartwood of the Tabebuia impetiginosa) extract. The results obtained using SWV agreed with those achieved by high-performance liquid chromatography.