Application of species-specific isotope dilution analysis to the correction for selenomethionine oxidation in Se-enriched yeast sample extracts during storage

This paper reports the advantages of isotope dilution analysis (IDA) in the correction for selenomethionine oxidation in Se-enriched yeast reference material extracts. Enzymatic hydrolysis was performed under two different conditions: by using ultrasound probe sonication for 2 min; and incubating at 37 degrees C for 24 h. [76 Se] SeMet isotopically labelled spike was added to the sample after Se species extraction, and 80 Se/76 Se and 78 Se/76 Se isotope ratios were measured as peak area ratios after HPLC-ICP-MS. The stability of the extracts obtained with both hydrolysis methods were evaluated by comparison of results of those immediately analysed with those stored for 24 h at different temperatures. The selenomethionine oxidation process showed a strong dependence on the extraction method used and the storage temperature, leading to biased selenomethionine content determinations. Species-specific isotope dilution analysis was successfully applied for the correction for such selenomethionine oxidation during storage.