Identification of anionic selenium species in Se-rich yeast by electrospray QTOF MS/MS and hybrid linear ion trap/orbitrap MSn.

An analytical approach allowing the identification of unknown selenium metabolites in selenium-rich yeast was described. Anion-exchange HPLC of the Se-metabolome fraction co-eluting with salts in size-exclusion chromatography allowed the separation of nine selenium species (excluding isomers and selenate) as monitored by inductively coupled plasma mass spectrometry (ICP MS). The individual fractions were analyzed by electrospray QTOF MS/MS and hybrid linear ion trap/Orbitrap MSn after sample introduction by reversed-phase nanoHPLC and by hydrophilic interaction LC (HILIC), respectively. Out of the nine detected species, eight were identified on the basis of accurate mass measurements and collision induced dissociation/fragmentation information. Seven Se-species (selenohomolanthionine, γ-Glu-selenocystathionine, 2,3-DHP-selenocystathionine, N-acetyl-selenocystathionine, 2,3-DHP-selenohomolanthionine, Se-methyl-selenoglutathione, and 2,3-DHP-Se-methylselenocysteine) were reported for the first time in Se-rich yeast, five of them have never been reported in any biological sample before.