Arsenic speciation in edible alga samples by microwave-assisted extraction and high performance liquid chromatography coupled to atomic fluorescence spectrometry

Twelve commercially available edible marine algae from France, Japan and Spain and the certified reference material (CRM) NIES No. 9 Sargassum fulvellum were analyzed for total arsenic and arsenic species. Total arsenic concentrations were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave digestion and ranged from 23 to 126 μg g−1. Arsenic species in alga samples were extracted with deionized water by microwave-assisted extraction and showed extraction efficiencies from 49 to 98%, in terms of total arsenic. The presence of eleven arsenic species was studied by high performance liquid chromatography–ultraviolet photo-oxidation–hydride generation atomic–fluorescence spectrometry (HPLC–(UV)–HG–AFS) developed methods, using both anion and cation exchange chromatography. Glycerol and phosphate sugars were found in all alga samples analyzed, at concentrations between 0.11 and 22 μg g−1, whereas sulfonate and sulfate sugars were only detected in three of them (0.6-7.2 μg g−1). Regarding arsenic toxic species, low concentration levels of dimethylarsinic acid (DMA) (<0.9 μg g−1) and generally high arsenate (As(V)) concentrations (up to 77 μg g−1) were found in most of the algae studied. The results obtained are of interest to highlight the need to perform speciation analysis and to introduce appropriate legislation to limit toxic arsenic species content in these food products

Investigating the potential of solid-phase extraction and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) for the isolation and identification of dissolved metal-organic complexes from natural waters

In aquatic environments, iron and copper often occur at low concentrations, and are bound to dissolved organic matter (DOM). The detection and chemical characterization of such iron- and copper-complexes are only slowly progressing due to the high diversity of natural DOM. Recent developments of sample preparation and measurement techniques have opened up new opportunities to selectively isolate and identify metal–organic compound groups from natural water samples. In this study, the isolation of the model complex desferrioxamine–iron (DFO–Fe) and naturally occurring iron- and copper–organic complexes from a groundwater and a seawater sample was investigated with a variety of solid-phase extraction (SPE) sorbents (polar to nonpolar) and extraction/elution (low and neutral pH) setups. Natural DOM, the model complex desferrioxamine–iron (DFO–Fe), and natural Cu-binding ligands were recovered in a range of 60–100% at low pH by the majority of the sorbents. In contrast, extraction efficiencies for solid-phase extractable iron–DOM and copper–DOM compounds (SPE-Fe–DOM and SPE-Cu–DOM) were overall lower and highly influenced by pH settings, sample type, and sorbent type. Especially, the SPE techniques preferentially isolated SPE-metal–DOM with neutral/weak acidic to basic characteristics, fractions which made up a relatively small amount (~ 10–15%) of the total natural SPE-DOM from the two water samples. Furthermore, our data indicate that solid-phase extractable small Fe–DOM colloids and acid-stable Fe- and Cu-organic compounds occur in natural DOM. A series of desferrioxamine–copper (DFO–Cu) and desferrioxamine–iron (DFO–Fe) calibration solutions were measured by ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), and both complexes were detectable in positive ion mode at concentrations as low as 150 nM (DFO–Cu) and 2 nM (DFO–Fe). DFO–Fe and DFO–Cu in the nM range were also detectable when added to a groundwater DOM sample to evaluate matrix effects by the natural DOM background. Our study demonstrates that SPE combined with high-resolution FT-ICR-MS is currently the most promising technique to isolate and unambiguously identify dissolved metal–organic complexes in highly diverse natural water samples

Determination of Water-Soluble Arsenic Compounds in Commercial Edible Seaweed by LC-ICPMS

This paper reports arsenic speciation in edible seaweed (from the Galician coast, northwestern Spain) produced for human consumption. Chondrus crispus, Porphyra purpurea, Ulva rigida, Laminaria ochroleuca, Laminaria saccharina, and Undaria pinnatifida were analyzed. The study focused on arsenosugars, the most frequently occurring arsenic species in algae. As(III) and As(V) were also determined in aqueous extracts. Total arsenic in the samples was determined by microwave digestion and inductively coupled plasma mass spectrometry (ICPMS). For arsenic speciation, a water extraction especially suitable for arsenosugars was used, and the arsenic species were analyzed by liquid chromatography with both anionic and cationic exchange and ICPMS detection (LC-ICPMS). The total arsenic content of the alga samples ranged from 5.8 to 56.8 mg As kg^–1. The mass budgets obtained in the extracts (column recovery × extraction efficiency) ranged from 38 to 92% except for <i>U. pinnatifida</i> (4%). The following compounds were detected in the extracts: arsenite (As(III)), arsenate (As(V)), methylarsonate (MA), dimethylarsinate (DMA), sulfonate sugar (SO₃-sug), phosphate sugar (PO₄-sug), arsenobetaine (AB), and glycerol sugar (Gly-sug). The highest concentrations corresponded to the arsenosugars