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

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. 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 trueness, 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 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.