Herbal Medicines: Application of a Sequential Voltammetric Procedure to the Determination of Mercury, Copper, Lead, Cadmium and Zinc at Trace Level

Background: The work describes the voltammetric determination of mercury(II), copper( II), lead(II), cadmium(II), zinc(II) by square wave anodic stripping voltammetry (SWASV) in herbal medicines. Methods: The voltammetric measurements were carried out using a conventional three electrode cell and two working electrodes, a gold electrode (GE) and a stationary hanging mercury drop electrode (HMDE). The analytical procedure was verified on the standard reference materials Spinach Leaves NIST-SRM 1570a, Tomato Leaves NIST-SRM 1573a and Apple Leaves NIST-SRM 1515. For all the elements, precision as repeatability, expressed as relative standard deviation (sr) was of the order of 4-6 %, while authenticity, expressed as relative error (e) was generally of the order of 5-8 %. Once set up on the standard reference materials, the analytical procedure was applied to commercial herbal medicine samples, and a critical comparison with spectroscopic measurements was done to evaluate the analytical performance. Results and Conclusion: Results are also processed by Principal Components Analysis (PCA), which provides very easy-to-read graphic outputs evidencing the influence of herbs prewashing on the content of risky elements. The correlation matrix is also obtained, allowing to study correlation between elements or methods.