Speciation Analysis of Arsenics in Commercial Hijiki by High Performance Liquid Chromatography-tandem-mass Spectrometry and High Performance Liquid Chromatography-inductively Coupled Plasma Mass Spectrometry

Edible brown alga (hijiki in Japanese, Hijikia fusiforme) contains not only a high content of inorganic arsenic (iAs) but also various arsenosugars (AsSugs) which are metabolized to dimethylarsinic acid (DMA) in mammals. Since DMA is considered to be carcinogenic in rodents, it is necessary to accurately measure the contents of AsSugs as well as iAs for the risk assessment of seaweed consumption. Seven commercially available dried-hijiki products and two raw hijiki products were analyzed. Total-As was measured by inductively coupled plasma mass spectrometry (ICP-MS) with the Dynamic Reaction Cell (DRC) mode after acid-digestion. After water-extraction, AsSugs were detected by HPLC-MS/MS with multiple reaction monitoring in the positive ion mode and speciation analysis of arsenics was performed by HPLC-ICP-MS. The ranges of total-As obtained by acid digestion (A-TAs) in nine hijiki samples were 37.1-118.6 mu g As/g dry weight (dw), and those of water extracted total-As (W-TAs) were 18.4-81.0 mu g As/g dw. The ratios of water extracted iAs (W-iAs) to A-TAs ranged from 24.5 to 60.1%. The major compound detected was arsenate in all samples (8.9-70.5 mu g As/g dw). Dimethylarsenosugar sulfate, AsSug 408, showed the highest peak among AsSugs detected. The content ratio of water extracted AsSugs (W-AsS) to A-TAs was estimated to be from 3.7 to 27.6%. The contents of A-TAs, W-iAs and W-AsS varied depending on the hijiki product. HPLC-MS/MS detected AsSugs more sensitively than HPLC-ICP-MS. Since iAs could not be detected by RPLC-MS/MS, combined analysis consisting of HPLC-MS/MS and HPLC-ICP-MS is necessary for accurate determination of arsenic species in seaweed products and also for the toxicological evaluation of AsSugs.