Accurate mass analysis and structure elucidation of selenium metabolites by liquid chromatography electrospray time-of-flight mass spectrometry

In this work, we describe a procedure for the structure elucidation of selenium compounds, based on accurate mass analysis of ions by means of liquid chromatography electrospray time-of-flight mass spectrometry (LC–TOFMS). It has been applied for the identification of novel Se species from the low-molecular-weight (LMW) range fraction of selenised yeast used for food supplements. The characterization of the suspected selenised species has been based on the information obtained from: (1) accurate mass measurements of both the protonated molecules and fragments from in-source CID fragmentation; (2) (high-resolution) isotopic signatures that are characteristic of selenium-containing ions and; (3) proposed elemental compositions and their double bond equivalent (DBE) values that can be used to assist the structure elucidation of new selenium species. Different examples on the identification of non-peptide selenium species are described in detail, including two selenised compounds that have been characterized here for the first time (i.e., m/z 426 and 513). Possible elemental compositions and structures of these selenised compounds were proposed on the basis of the data collected by LC–TOFMS, and the advantages and drawbacks of the proposed approach are critically discussed. The signal-to-noise ratio obtained for the detected selenised compounds in LC–TOFMS analyses was clearly higher than using LC–ICPMS detection.