Determination of Mercury in Chinese-Prepared Medicine Using Closed Vessel Microwave Digestion with Cold-Vapor Atomic Absorption Spectrometry

A method that is both simple and rapid for the determination of mercury in Chinese-prepared medicine (CPM) was developed. The method uses closed-vessel microwave digestion with final analysis by CVAAS with a sodium borohydride and hydroxylammonium hydrochloride solution. The accuracy of the method was checked using botanical-certified reference materials (BCR62, olive leaves), and close agreement with certified values was achieved. The precision of the method, based on different types of CPM samples and different analysts on different days at different levels of mercury, was found to be between 5.0 and 13.3% (relative standard deviation, n = 6). A comparison between two different types of vessels for closed-vessel microwave digestion was performed. Potential matrix interference, such as undecomposed organics and others in CPM samples, was investigated. The effect of a hydroxylammonium hydrochloride solution was also investigated, and was found to have a strong impact on the accuracy of the method. Finally, the method was used to prepare in-house reference materials. A simpler approach of using a statistical quality control (SQC) chart was used to assess the stability of the reference materials and to monitor the stability of the analytical procedures.