Analysis of Arsenic and Mercury Species from Botanicals and Dietary Supplements using LC-ICP-MS

Speciation of arsenic and mercury is very important because the toxicity and the bioavailability of these elements are related to their chemical form [1]. The inorganic species, As III (arsenite) and As V (arsenate), are considered to be carcinogenic, whereas the toxicity of the organic species is variable. The various chemical forms of mercury have different toxicities, with MeHg species being more toxic than inorganic mercury compounds [1]. Identification and quantitative determination methods of arsenic and mercury species from botanicals and dietary supplements are discussed.

Arsenic and mercury speciation analyses were performed on nine dietary supplements where total arsenic or mercury was found to be high. The samples were analyzed using gradient elution anion exchange high-performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Solvent extraction with sonication and microwave extraction using various aqueous and aqueous/solvent mixtures was initially evaluated. Six arsenic species (arsenic acid (As III), arsenous acid (As V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AB), and arsenocholine (AC)) and three mercury species (MeHg, HgCl₂ and EtHg) were determined. The speciation data presented here may be valuable for quality assurance of analytical method development and surveys of arsenic or mercury from dietary supplements. The most abundant species found were arsenite, arsenate, dimethylarsinic acid and HgCl₂. Total arsenic species dosages in the commercial products analyzed ranged from 0.1 to 31µg/day. The relative concentrations of inorganic arsenic in the samples ranged from 59 to 89% of the total arsenic species detected in each sample. HgCl₂ was detected in all samples and MeHg was not detected in any of the samples analyzed. The maximum tolerable daily intake of inorganic arsenic of 150µg/day for an average body weight of 70kg and provisional tolerable weekly intakes (PTWI) of MeHg to 1.6µg per kg body weight per week are established by the Joint FAOWHO Expert Committee on Food Additives (JECFA). All samples analyzed are within limits of JECFA

Fig.1: HPLC-ICP-MS chromatograms of (A) Hg standard mix [Hg²⁺ (1), Me-Hg (2) and Et-Hg (3)]; (B) As standard mix [AsC (1), AsB (2), As (III) (3), DMA (4), MMA (5) and As (V) (6)] and samples

Acknowledgements : This research is supported in part by Science Based Authentication of Dietary Supplements funded by the Food and Drug Administration grant No. 1U01FD004246–01; the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58–6408–2-0009, and the Global Research Network for Medicinal Plants (GRNMP), King Saud University The authors would like to thank Annette Ford for extraction of the plant samples. References: [1] Caroli S, (1996) Element Speciation in Bioinorganic Chemistry, Wiley, Chapter 13.