The concerted application of element specific atomic spectral detection for chromatographic eluent monitoring allows previously unexploited qualitative and quantitative analytical concepts to be developed for the determination of selenium species. Selenium speciation is vital in order to better understand its metabolism and biological significance in clinical chemistry, biology, toxicology, and nutrition. Fluoroacid ion pair HPLC with ICP-MS detection and GC derivatization with atomic emission detection (AED) together aid analysis and elucidation of reaction pathways of selenium compounds in high selenium enriched yeast, as used widely in nutritional and clinical cancer preventative studies. Comparisons between currently produced and archived selenized yeasts show major differences in speciation. The formation of selenomethionine selenoxide and the identification of Se-S bonded S-(selenomethyl)-cysteine in archived nutritional yeast may be important for short and long term stability and nutritional activity studies.

After proteolytic digestion, aqueous extraction, and derivatization with diethyl pyrocarbonate or ethyl chloroformate, HPLC-inductively coupled plasma (ICP)-MS, GC-atomic emission detection (AED), and GC-MS analysis of high-selenium yeast stored at room temperature for more than 10 years showed selenomethionine as the major Se product along with substantial amounts of selenomethionine selenoxide hydrate and the previously unreported selenoamino acid having a Se-S bond, S-(methylseleno)cysteine. The identity of the latter compound was confirmed by synthesis. The natural product was shown to be different from a synthetic sample of the isomeric compound Se-(methylthio)selenocysteine. Selenium-specific NMR spectroscopic methods were developed to directly analyze the aqueous extracts of the hydrolyzed selenized yeast without derivatization or separation. Selenomethionine and S-(methylseleno)cysteine were identified by 77 Se-1 H HMQC-TOCSY experiments.