A BiFEs-based SWASV method for fast screening of multi-heavy metals in Xiaochaihu Tang

Multi-heavy metal residues in traditional Chinese medicines especially their formulas have become a world-wide concern for human's health. A real time analysis of multi-heavy metals with high sensitivity and accuracy is of great necessity. In this study, an anodic square wave stripping voltammetry (SWASV) technique based on the stable Bismuth material was developed for the fast screening of Cd2+, Pb2+ and Cu2+ in Xiaochaihu Tang for its safe medication in practice. Firstly, a flat and compact Bismuth film electrode (BiFE) was prepared by pre-plating Bi crystal on glass carbon electrode (GCE) substrate at special deposition potential and deposition time, which was confirmed through the observation of morphological and electrochemical properties. Then, the heavy metals of interest were isolated from complex Xiaochaihu Tang by using an optimized digestion system and a low-cost sample preparation procedure. Besides, three different deposition potentials were selected to respectively reduce 3 kinds of cations for a better reproducibility and accuracy of the analysis than before. It was demonstrated that the intensity of the remarkable anodic peaks of Cd2+, Pb2+ and Cu2+ at −0.876 V, −0.621 V and − 0.248 V were proportional (R2 = 0.9975, 0.9993, 0.9997) to their concentrations in the decoction electrolyte in the range of 0.008-0.08 μg·mL−1 for Cd2+, 0.01-0.1 μg·mL−1 for Pb2+ and 0.10-1.00 μg·mL−1 for Cu2+, respectively. The developed SWASV method allowed low detection limits of 0.0031 μg·mL−1, 0.0002 μg·mL−1 and 0.0044 μg·mL−1 for Cd2+, Pb2+ and Cu2+, which are much lower than the guideline values in herbs set in the Chinese Pharmacopeia. Real sample analysis showed that Pb2+ was detected in 3 batches of Xiaochaihu Tang samples within 5 min, which were confirmed by the ICP-MS method. Therefore, this developed method can be applied in the fast screening of multi-heavy metals in complex decoction matrices.