Stability of selenium compounds in aqueous extracts of dietary supplements during storage.

The stability of two inorganic (selenite Se (IV) and selenate Se(VI)) as well as four organic (selenomethionine (SeMet), selenocystine (SeCys), selenomethylocysteine (MeSeCys) and selenomethionine selenoxide (SeMetO)) selenium species were investigated in standard solutions and aqueous extracts of dietary supplements. All of the samples were without any stabilizer addition. The effect of the sample solvent pH and the storage temperature was investigated using hydrophilic interaction liquid chromatography coupled to mass spectrometry detection (HILIC-MS). It was proven that sample solvent has a great impact on the selenium stability. The lowest stability of selenium compounds is observed in ammonium acetate samples. Acidification of the solution increase the selenium stability (with the exception of SeMet in yeast sample). The results of the stability of selenium compounds obtained for the standard solutions are different than those for supplement samples, which shows the enormous influence of the sample matrix on the stability of selenium compounds. Light does not affect selenium stability in standard solutions as well as in supplements extracts.