Determination of arsenic and mercury in Chinese medicinal herbs by atomic fluorescence spectrometry with closed-vessel microwave digestion

A simple method was developed for the determination of trace arsenic and mercury in Chinese medicinal herbs. The samples were digested in closed-Teflon vessels in a microwave oven, and followed with hydride generation atomic fluorescence spectrometric measurements. The experimental conditions for the digestion were carefully optimized using an orthogonal design. The accuracy of the method was validated by recovery experiments, and the analytical results for arsenic in seven medicinal herbs (Codonopsis pilosula, Radix angelicae sinensis, Aconitum carmichaeli debx, crude aconite root, giant typhonium rhizome, Rhizoma typhonii, and Radix aconiti lateralis preparata) were found to agree well with those by inductively coupled plasma atomic emission spectrometry (ICP-AES). The linear dynamic range of the calibration curve was in the range of 0.1-400 ng/mL for arsenic, and the correlation coefficient was better than 0.999. The limit of detection was 0.1 ng/mL for arsenic. For mercury, the determination was accomplished through mercury cold vapor generation in the same instrumental system. The linear dynamic range was 0.03-250 ng/mL, with a limit of detection of 0.03 ng/mL for mercury. This was a rapid, convenient, precise, and cost-effective method.