Characterization of arsenosugars of biological origin using fast atom bombardment tandem mass spectrometry.

A fast atom bombardment (FAB) mass spectrometric method has been developed for characterizing arsenosugar compounds. These compounds are of particular interest not only because their biochemistry requires further investigation but also because they are present at relatively high concentrations in commercial seaweed food products. FAB was used for the efficient generation of gas-phase ions of the various arsenosugar compounds. Negative-ion detection of such ions was found to be more sensitive than positive-ion detection due to the presence of negatively charged substituents. Negative-ion collision-induced dissociation (CID) tandem mass spectrometry (MS) of the [M - H](-) precursor ions results in the formation of numerous characteristic product ions via charge-remote fragmentation. These product ions provide abundant structural information for arsenosugar characterization. Separation of the arsenosugar-originating precursor ions from the matrix ions, always present in FAB mass spectra, is achievable using an analyzer resolution of 3000. This resolution allows for accurate selection of a precursor ion for subsequent CID experiments. However, by switching to a resolution of 1000, the quality of the tandem mass spectra can be slightly improved. Such an improvement is especially useful when analyzing nanogram amounts of arsenosugars. Furthermore, it was demonstrated that positive-ion tandem MS provides complementary information for the structural characterization of the arsenosugars examined. The mass spectrometric procedures developed in this study were further applied for the characterization an arsenosugar present in a partially purified algal (Sargassum lacerifolium) extract.