Separation and Analysis of Arsenic Species in Dietary Supplements using LC-ICP-MS

Speciation of arsenic is very important as the toxicity and the bioavailability are related to the chemical form. The inorganic species, As III (arsenite) and As V (arsenate), are considered carcinogenic, whereas the toxicity of the organic species is variable. The methylated forms, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), are much less toxic. More complex forms as arsenobetaine (AB) and arsenocholine (AC) are considered non-toxic [1]. Arsenic speciation analysis was performed in nine dietary supplements where total arsenic 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, including arsenic acid (As III), arsenous acid (As V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AB), and arsenocholine (AC) were determined. The speciation data presented here may be valuable for the quality assurance of analytical method development and surveys of arsenic in dietary supplements. The three most abundant arsenic species found were arsenite, arsenate and dimethylarsinic acid. Total arsenic species concentrations in the commercial products analyzed ranged from 0.1 to 31µg/day. By using HPLC-ICP-MS, the relative amount of inorganic arsenic in the samples ranged from 59 to 89% of the sum of the arsenic species detected in each sample. The maximum tolerable daily intake of inorganic arsenic of 150µg/day for an average body weight of 70kg was established by the Joint FAOWHO Expert Committee on Food Additives (JECFA). All samples analyzed are within limits of JECFA.

Figure 1: HPLC-ICP-MS chromatograms of standard mix [AsC (1), AsB (2), As (III) (3), DMA (4), MMA (5) and As (V) (6)] and samples (#3871, #3876)

Acknowledgements: This research is supported in part by „Science Based Authentication of Dietary Supplements“ and „Botanical Dietary Supplement Research“ funded by the Food and Drug Administration grant numbers 5U01FD002071–10 and 1U01FD003871–02, and the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58–6408–2-0009 and the authors would like to thank Dr. Mei Wang for the extractions of plant samples.

References: [1] Caroli S, et al, (1996) Element Speciation in Bioinorganic Chemistry, Wiley, Chapter 13.