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

Overview

Shimoda and colleagues measured total arsenic, water-extracted inorganic arsenic, and arsenosugar species in seven commercially available dried-hijiki products and two raw hijiki samples. The occurrence-relevant matrix is hijiki seaweed on a dry-weight basis, with source-region and production-system context retained from Table 1. Total arsenic, water-extracted total arsenic, inorganic arsenic, DMA, and individual arsenosugar peaks are kept separate below.

Key numbers

Table 1 identifies the nine hijiki samples:

Table 4 reports acid-digested total arsenic and water-extracted arsenic fractions in µg As/g dw; each sample solution was measured in triplicate and values are mean ± S.D. (n = 3). No unit conversion was performed.

Table 3 reports water-extracted arsenic compounds by HPLC-ICP-MS in µg As/g dw; values are means (n = 3). ND means not detected by HPLC-ICP-MS, and the AsSug 328 peak includes unresolved AsBe and AsSug 254 according to the table footnote.

Source-reported summary statements:

• Acid-digested total arsenic in the nine hijiki samples ranged from 37.1 to 118.6 µg As/g dw.
• Water-extracted total arsenic ranged from 18.4 to 81.0 µg As/g dw.
• The major water-extracted compound was arsenate in all samples (8.94 to 70.52 µg As/g dw in Table 3).
• Water-extracted arsenosugars represented 3.7 to 27.6% of acid-digested total arsenic.
• AsSug 408 was the major arsenosugar peak in the water extracts.
• The authors state that HPLC-MS/MS detected arsenosugars more sensitively than HPLC-ICP-MS, but HPLC-MS/MS could not detect inorganic arsenic; they therefore recommend combined HPLC-MS/MS and HPLC-ICP-MS for seaweed arsenic-speciation work.

Methods (brief)

Commercial dried-hijiki products and two raw hijiki samples were ground to powder. Total arsenic was measured by ICP-MS with dynamic reaction cell mode after acid digestion of 20 mg powdered sample with 0.5 ml HNO3 and 0.5 ml H2SO4 at 330 °C for 1 hr, dilution to 50 ml, and standard addition calibration; NIES CRM No. 18 urine was used to validate total arsenic, AsBe, and DMA measurements. Speciation extracts used 0.5 g powdered hijiki swollen with 20 ml ultra-pure water, ultrasonic disruption for 1 min, centrifugation at 3000 rpm for 15 min, and adjustment of supernatant to 50 ml. Arsenosugars, AsBe, DMA, and MMA were detected by HPLC-MS/MS with multiple reaction monitoring; arsenic species and water-extracted species totals were measured by HPLC-ICP-MS with PRP-X100 anion-exchange chromatography.

Implications

This source contributes primary occurrence evidence for hijiki seaweed with total arsenic and inorganic arsenic separated in the same samples. The commercial dried-hijiki products had acid-digested total arsenic from 37.1 ± 1.2 to 118.6 ± 11.3 µg As/g dw, while water-extracted inorganic arsenic ranged from 9.2 ± 0.4 to 71.3 ± 2.0 µg As/g dw across all nine samples. The raw and processed hijiki rows should remain on the source’s dry-weight basis, and total arsenic, arsenate/arsenite, DMA, and arsenosugar peaks should not be collapsed into a single arsenic species.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Seaweed
• Arsenic, Total
• Arsenic, Inorganic

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