Simple and sensitive electrochemical determination of higenamine in dietary supplements using a disposable pencil graphite electrode

In this study, a cheap, rapid, simple, and modification-free electroanalytical methodology based on the disposable pencil graphite electrode is described for the quantification of higenamine (isoquinoline-type alkaloid having three phenolic OHs). At first, the electrochemical oxidation of higenamine was investigated in aqueous solutions by cyclic voltammetry. The electrode process is pH-dependent and controlled by a mixture of diffusion and adsorption processes. Higenamine yielded two well-separated oxidation steps in acidic, neutral, and alkaline media by using square-wave voltammetry. By using the first oxidation peak due to its higher sensitivity, there was an excellent correlation between oxidation peak current at + 0.44 V and higenamine concentration (as hydrochloride salt) in the range of 0.05 to 2.0 mu g cm(-3) (1.63 x 10(-7)-6.5 x 10(-6) mol dm(-3)), with a detection limit of 0.014 mu g cm(-3) (4.55 x 10(-8) mol dm(-3)) in Britton-Robinson buffer at pH 4.0. As an example, the developed approach can be used for the quantification of higenamine in the commercial dietary supplement formulations. Graphic abstract