Sulfide oxidations for LC-MS analysis of methionine-containing microcystins in dolichospermum flos-aquae NIVA-CYA 656

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DOIResolve DOI: https://doi.org/10.1021/es5029102
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  1. National Research Council of Canada. Measurement Science and Standards
FormatText, Article
Journal titleEnvironmental Science and Technology
ISSN0013-936X
Volume48
Issue22
Pages13307–13315
SubjectAmino acids; Extraction; Inert gases; Lc-ms analysis; Oxidation state; Rapid extraction; Sample extraction; Sulfide oxidation; mercaptoethanol; methionine; methionine sulfoxide; microcystin; oxidation; oxide; peptide; sulfide; algal bloom; Anabaena; bacterium culture; derivatization; Dolichospermum flos aquae; high performance liquid chromatography; liquid chromatography; mass spectrometry; signal noise ratio; tandem mass spectrometry; ultra performance liquid chromatography; algae; Cyanobacteria; Flos
Abstract
Microcystins are cyclic heptapeptides produced by a range of cyanobacteria. More than 150 microcystin analogues have been reported from cultures, algal blooms, or other contaminated samples. Relatively few analytical standards are available, making identification and quantitation of these toxins a challenge, even with LC-MS technology. We developed a two-step oxidative procedure that allows LC-MS identification of microcystins containing methionine and methionine sulfoxide, and reveals the oxidation state of the methionyl sulfur atom. The procedure was used in parallel with mercaptoethanol derivatization and LC-MS2 analysis to demonstrate the presence of [Asp3]MC-MR (12) and MC-MR (17) in a culture of Dolichospermum flos-aquae, together with low levels of [Asp3]MC-M(O)R (5) and MC-M(O)R (7), as well as 20 other microcystins. Fresh culture contained only traces of sulfoxides 5 and 7, but these increased during storage or sample extraction and preparation. This suggests that microcystins containing methionine sulfoxide are primarily postextraction oxidation artifacts, rather than being produced by biosynthesis in cyanobacteria. A simple, rapid extraction under inert gas followed promptly by LC-MS analysis minimized oxidation artifacts for D. flos-aquae.
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PublisherACS Publications
LanguageEnglish
Peer reviewedYes
NPARC number21275551
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