Arsenic speciation in freshwater fish using high performance liquid chromatography and inductively coupled plasma mass spectrometry

Arsenic speciation in freshwater fish is crucial for providing meaningful consumption guidelines that allow the public to make informed decisions regarding its consumption. While marine fish have attracted much research interest due to their higher arsenic content, research on freshwater fish is limited due to the challenges in quantifying and identifying arsenic species present at trace levels. We describe here a sensitive method and its application to the quantification of arsenic species in freshwater fish. Arsenic species from fish tissues were extracted using a methanol/water mixture (1:1 vol. ratio) and ultrasound sonication. Anion-exchange high-performance liquid chromatography (HPLC) enabled separation of arsenobetaine (AsB), inorganic arsenite (iAs^III), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenate (iAs^V), and three new arsenic species. Inductively coupled plasma mass spectrometry (ICPMS) provided highly sensitive and specific detection of arsenic. A limit of detection of 0.25 µg/kg (wet weight fish tissue) was achieved for the five target arsenic species: AsB, iAs^III, DMA, MMA, and iAs^V. A series of experiments were conducted to ensure the accuracy and validity of the analytical method. The method was successfully applied to the determination of arsenic species in lake whitefish, northern pike, and walleye, with AsB, DMA, and iAs^V being frequently detected. Three new arsenic species were detected, but their chromatographic retention times did not match with those of any available arsenic standards. Future research is necessary to elucidate the identity of these new arsenic species detected in freshwater fish.