McSheehy and Szpunar 2000 - arsenic speciation in edible algae

McSheehy and Szpunar developed a two-dimensional SE-AE-HPLC-ICP-MS and ESI-MS/MS workflow for arsenosugar identification in edible algae extracts. The occurrence-relevant table reports total arsenic and “mineral” arsenic in commercially available edible algal products on the French market. The sample frame was enriched for products already withdrawn because of high mineral arsenic, so the values are direct measurements but not a random market survey.

Key numbers

Table 2 reports concentrations as mg kg-1. The paper uses “mineral arsenic” for the inorganic/mineral fraction separated as AsCl3 by distillation from organoarsenic compounds. No unit conversion was performed.

The results text states that total arsenic in the investigated samples varied from 3.5 to 134 mg kg-1, with mineral arsenic constituting 36–74%; the remaining arsenic was presumed to be arsenosugars on the basis of earlier literature. The authors specifically note that Hizikia and Laminaria contained about 10 times higher organic arsenic than the other algae products and were used as model samples for analytical-procedure development.

Reference-material and method figures:

• Reference algae (Laminaria digitata) mineral arsenic was 72±7 mg kg-1 across 8 analyses, compared with a recommended value of 61 mg kg-1.
• Reference algae total arsenic was 124±6 mg kg-1 across 5 analyses, compared with a recommended value of 145 mg kg-1.
• For total/mineral arsenic, 0.5 g algae was digested overnight with 5 mL of 65% HNO3, diluted with 35 mL water, and further digested at 90 °C.
• For arsenosugar extraction, 1 g algae was extracted with methanol-water mixtures; a 50:50 v/v methanol-water mixture was found optimum and gave extraction yields exceeding 85%.

Table 1 method conditions:

• Anion-exchange HPLC column: Supelcosil SAX1; mobile phase 5 to 30 mM phosphate buffer at pH 6 within 22 min; flow 1.0 mL min-1.
• Size-exclusion HPLC column: Superdex Peptide HR 10/30; mobile phase 1% aqueous acetic acid at pH 3; flow 0.6 mL min-1.
• ICP-MS conditions: forward power 1100 W, nebulizer gas flow 1.05 L min-1, monitored isotope 75As, dwell time 60 ms.
• ESI-MS/MS conditions: orifice 20 V, ionspray voltage 4100 V, scan range 70–500 u within 8.6 s, dwell time 1 ms, step size 0.05 u.
• MS CID MS conditions: parent ions 483 and 409, collision energy 20 eV, product-ion scan range 70–500 within 7.17 s, dwell time 5 ms, step size 0.3 u, multiplier voltage 2400 V.

Arsenosugar/speciation context:

• In crude anion-exchange chromatograms of Hizikia fusiforme, peak labels were ambiguous: peak 1 was “arsenosugar B or As(III)”, peak 2 was DMAA, peak 3 was arsenosugars D/A or MMAA, peak 4 was arsenosugar C, and peak 5 was As(V).
• Size-exclusion followed by anion-exchange HPLC improved identification. Fraction I contained arsenosugar D with arsenosugar A about 5–10 times lower; fraction II contained arsenosugars D, A, and C partly separated; fraction III confirmed MMAA and DMAA; fraction IV contained As(V).
• ESI-MS/MS identified arsenosugar D in fraction I (m/z 483.0) and arsenosugar C in fraction II (m/z 408.9). No signals above 3 times noise were detected in fractions III and IV by ESI-MS.

Methods (brief)

The study analyzed dried algal food products commercially available on the French market, supplied by the regional D.G.C.C.R.F. agency in Bordeaux. Commercial products were soaked in cold water for 10 min before preparation for soups or salads; powdered samples were transferred to plastic bottles. Total arsenic was measured by GFAAS after nitric-acid digestion. Mineral/inorganic arsenic was measured by the Whyte and Englar distillation method, separating inorganic arsenic as AsCl3 from organoarsenic compounds. Organoarsenic species were extracted using methanol-water mixtures and investigated by size-exclusion HPLC, anion-exchange HPLC, ICP-MS detection, and ESI-MS/MS.

Implications

This source contributes historical direct occurrence evidence for French-market edible algae with elevated mineral/inorganic arsenic, especially Hizikia fusiforme and Laminaria. It is routeable to seaweed/kelp foods, but downstream extraction should preserve its biased sample frame: the products had been withdrawn because mineral arsenic was above roughly 3 mg kg-1, so these measurements should not be treated as an unselected market distribution. Total arsenic, mineral/inorganic arsenic, DMAA/MMAA, and arsenosugars must remain separate; the arsenosugar findings are speciation context, not inorganic arsenic.

Wiki pages this source may touch

• seaweed-kelp-foods
• seaweed
• arsenic-total
• arsenic-inorganic

Verification notes

• Identity checks before writing found no existing source page for RSC paper code a906890b, inferred DOI 10.1039/a906890b, raw handle MFK_mcsheehy2000, title text, or cite key mcsheehy2000-edible-algae-arsenic-speciation.
• Text was extracted to /tmp/hmi-seaweed-048.txt with pdftotext -layout; title, abstract, Tables 1-2, methods, results, figures captions, conclusions, and paper code were readable.
• All Key numbers were checked against /tmp/hmi-seaweed-048.txt, especially Table 2 and the total/mineral arsenic Results paragraph. The source’s printed mg kg21 notation is recorded as mg kg-1.
• Units and bases are preserved as mg kg-1, mg mL-1, mg ml-1, ng mL-1, mM, mL min-1, W, V, and %; no unit conversion was performed.
• Speciation check: “mineral arsenic” is treated as the source’s inorganic/mineral arsenic fraction. Total As, arsenosugars, As(V), As(III), DMAA, and MMAA are kept distinct and not collapsed into one species label.
• Brand firewall: no consumer brands are named. The D.G.C.C.R.F. agency and analytical-instrument vendors are scientific/provenance context, not product brand attribution.
• Missing-slug check: no missing product or ingredient slug blockers. Exact algae species, origins, and the non-edible Sargassum lacerifolium row remain in Key numbers while frontmatter uses broad seaweed/kelp food routing.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.