Evaluation of yeast-based selenium food supplements using high-performanceliquid chromatography and inductively coupled plasma mass spectrometry

Six different brands of yeast-based selenium food supplements were obtained from local stores. These samples were analyzed for total selenium content and content uniformity by microwave nitric acid digestion. These supplement s were also treated with milder extraction and hydrolysis conditions to ana lyze for the expected selenomethionine, a natural product of yeast when ino culated with selenium. A C8 high-performance liquid chromatographic (HPLC) column was used for the chromatographic determination of selenomethionine u sing a mobile phase of 89+10+1 (v/v/v) water-methanol-trifluoroacetic acid. Inductively coupled plasma mass spectrometry (ICP-MS) was used for the tot al selenium content and tablet content uniformity determination, and ICP-MS was used as the detector coupled with HPLC for the selenomethionine determ ination. A number of extraction and hydrolysis sample treatment procedures were tried. The two most effective appeared to be microwave heating with hy drochloric acid and with a simple overnight treatment with the enzyme Prote inase K. The six different brands of selenium supplements were found to hav e near label values based on total selenium, and they had reasonable tablet to tablet content uniformity values, but each brand had dramatically diffe rent profiles for the actual chemical form of selenium within the supplemen t. Only two brands had high levels of selenomethionine; one brand appeared to contain all inorganic selenium, and one brand appeared to contain greate r than half inorganic selenium despite label claims of content being only s elenomethionine.