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Arsenic Speciation and Fucoxanthin Analysis from Seaweed Dietary Supplements Using LC-MS

Bharathi Avula, Yan-Hong Wang, Ikhlas A. Khan
Journal of AOAC International 2015 v.98 no.2 pp. 321-329
anion exchange, arsenates, arsenic, arsenites, cacodylic acid, carotenoids, chemical speciation, detection limit, dietary exposure, dietary supplements, extraction, high performance liquid chromatography, humans, macroalgae, mass spectrometry, medicinal properties, solvents, surveys, toxicity, wet digestion method
The study involves the analysis of total arsenic (As) in metallic form, and organic and inorganic As species from seaweeds and dietary supplements. The analysis provides data for dietary exposure estimates of inorganic species that are considered more toxic to humans than organic and total As. Total As was determined by acid digestion followed by inductively coupled plasma (ICP)-MS. To characterize the As species, solvent extraction with sonication and microwave extraction using various aqueous and aqueous/organic solvent mixtures were initially evaluated. The optimum As speciation method was determined to be water extraction followed by anion exchange HPLC coupled with ICP-MS. Optimization of chromatographic conditions led to baseline separation for six As species, including As acid, arsenous acid, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, and arsenocholine, in approximately 8 min using gradient elution. Detection limits for all six compounds were in the range of 10–15 ng/mL. The data presented here will be valuable for the QA of analytical method development and surveys of total As and As species in dietary supplements. The most abundant As species found were arsenite [As(III)] and arsenate [As(V)]. The sum of inorganic As species present in the dietary supplements ranged from 1.2 to 31 μg/day. In addition, the dietary supplements purported to contain fucoxanthin, a carotenoid having pharmacological activities, were analyzed using ultra-performance LC-UV/MS.