Arsenic speciation in Chinese seaweeds using HPLC-ICP-MS and HPLC-ES-MS

Abstract

Three common Chinese edible seaweeds, one brown (Laminaria japonica) and two red (Porphyra crispata and Eucheuma denticulatum), were examined for their total arsenic content. The As species were extracted with yields of 76.4, 69.8 and 25.0%, respectively. Anion-exchange and cation-exchange high-performance liquid chromatography (HPLC) in combination with inductively coupled plasma mass spectrometry (ICP-MS) were used for the separation of the different arsenic species in two of the three seaweed extracts (Laminaria and Porphyra). The main arsenic species in the algal extracts are arseno sugars, although it has been shown that the Laminaria seaweed contains significant amounts of dimethylarsinic acid (DMA). HPLC was coupled with electrospray mass spectrometry (ES-MS) for structural confirmation of the arsenic species. The mass spectrometer settings for the arseno sugars were optimised using standards. The conclusions drawn on the basis of HPLC-ICP-MS were confirmed by the HPLC-ES-MS data. The HPLC-ES-MS method is capable of determining both arseno sugars and DMA in the seaweeds. The unknown compounds seen in the HPLC-ICP-MS chromatogram of Laminaria could not be ascribed to trimethylarsenic oxide or tetramethylarsonium ion.