Identification of the major selenium compound, Se-Methionine, in three yeast (Saccharomyces cerevisiae) dietary supplements by on-line narrowbore liquid chromatography–electrospray tandem mass spectrometry

On-line monitoring of six Se-compounds was accomplished by using an XTerra MS C18 column coupled to electrospray tandem mass spectrometry (ES–MS–MS). In view of the nature of the compounds, the positively charged ion pairing agent tetraethylammoniumchloride (TEACl) was added to the mobile phase. The HPLC–ES–MS–MS method was optimized with six commercially available Se-compounds. Substitution of the analytical column by the narrowbore type significantly enhanced the sensitivity of the method. We were able to detect the m/z of these six molecules on-line. Furthermore, all product ions could be monitored. The method was applied to three different yeast-based supplements. They were submitted to proteolytic digestion and screened for their Se-content by HPLC–HG–AFS (hydride generation-atomic fluorescence spectrometry). By application of on-line narrowbore HPLC–electrospray tandem mass spectrometry, the main compound present in these three supplements, Se-Methionine, could be measured on its m/z and its product ions. The method can be further extended for on-line measurement of different Se-species in complex matrices