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