Environmental Context. A new group of arsenic compounds, namely thio-arsenosugars, has recently been discovered in some marine samples, including seafood products. We do not yet understand how these arsenic compounds are produced by living organisms, nor do we know their implications for human health. Their unusual chromatographic properties are the reason that they are difficult to detect by existing methods. We present a new method for finding these thio-arsenosugars, and we also report two new thio-arsenosugars.

Abstract. Two new thio-arsenosugars were identified in aqueous and methanol extracts from the gonad and the muscle of the great scallop by using high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICPMS) and HPLC–electrospray ionization mass spectrometry (ESMS). The gonad of the scallops contained thio-arsenosugar–sulfonate [0.067 mg (As) kg^-1; dry mass ± 3.7%] and thio-arsenosugar–sulfate [0.267 mg (As) kg^-1; dry mass ± 1.2%]. The muscle also contained both thio-arsenosugar–sulfonate [0.030 mg (As) kg^-1; dry mass ± 2.6%] and thio-arsenosugar–sulfate [0.200 mg (As) kg^-1; dry mass ± 2.6%]. Methanol increased the extraction efficiency threefold for the two thio-arsenosugars as compared to water. Fresh and freeze-dried samples from both parts of the scallop showed no significant difference with respect to the concentration of the two thio-arsenosugars. In order to confirm the presence of the thio-arsenosugars, a new method for their determination with HPLC–ESMS was developed. Under optimized conditions [Hamilton PRP-X100; 150 by 1.0 mm; 20 mM NH₄HCO₃ with 55% (v/v) methanol at pH 10.3] we succeeded in determining the pseudomolecular ions of thio-arsenosugar–glycerol, thio-arsenosugar–phosphate, thio-arsenosugar–sulfonate, and thio-arsenosugar–sulfate at concentrations less than 5 µg (As) dm^-3 in standard solutions and real samples.