Determination of Heavy Metals in Botanicals and Dietary Supplements by Using Collision/Reaction Cell ICP-MS: Comparison of Microwave Digestions Assisted by Six Types of Digestion Mixtures

Heavy metals are natural components of the earth's crust and are widely used in agricultural, manufacturing and food/material processing industries. Some heavy metals such as selenium, iron, copper, chromium and zinc are essential at low concentrations, others such as arsenic, cadmium, lead and mercury are toxic. Determination of 11 metals (including arsenic, chromium, mercury, iron, copper, nickel, zinc, selenium, lead, cadmium and thallium) in botanicals and dietary supplements were carried out by using ICP-MS. Closed vessel microwave digestion of two plant samples and one product assisted by HNO₃+HCl (8:2) (Procedure-A), water (Procedure-B), methanol (Procedure-C), HNO₃ (Procedure-D), 0.5 M HCl (Procedure-E) and HNO₃ +6 M HCl (Procedure-F) were used to determine the recovery of 11 metals by ICP-MS. Sample digestion was done in a MARS 5 microwave. Elemental measurements were performed using Agilent 7500 ce CRC-ICP-MS operating in hydrogen mode for Se and Fe, and He mode for As, Cr, Cu, Ni, Cd to remove spectral interferences. The method was validated for linearity, repeatability, limits of detection (LOD) and limits of quantification (LOQ). The limits of detection and limits of quantification for these heavy metals were found to be 0.004–0.51 ppb. Digestions A, D and F gave significantly higher recoveries than compared with other digestions. Microwave digestion followed by analysis by ICPORS-MS has been shown to be a simple, reliable method for the multi-element determination of trace metals in dietary supplements and botanicals. About 12 plant samples and 22 dietary products were analyzed and all were found to contain Fe, Zn, Cu, Cr, and Ni. Four samples for As and one sample for Cr were found to contain elevated concentrations above the recommended limit. Acknowledgements: This research is funded in part by “Science Based Authentication of Dietary Supplements” Funded by the Food and Drug Administration grant number 2 U01 FD 002071-07. References: [1] Dolan SP, et al. (2003), J Agric & Food Chem, 51: 1307–1312.

Fig. 1 Extraction (A) and Heavy Metal analysis of Botanicals and Dietary Supplements (B) using ICP-MS method.