title: Determination of methionine and selenomethionine in selenium-enriched yeast by species-specific isotope dilution with liquid chromatography-mass spectrometry and inductively coupled plasma mass spectrometry detection.
abstract: Selenomethionine (SeMet) and methionine (Met), liberated by acid hydrolysis of selenium-enriched yeast, were quantified by liquid chromatography-mass spectrometry (LC/MS) using standard additions calibrations as well as isotope dilution (ID) based on species-specific (13)C-enriched spikes. LC inductively coupled plasma mass spectrometry (ICPMS) was also employed for the quantification of SeMet, and (74)Se-enriched SeMet was used for ID calibration. The results were evaluated to ascertain the feasibility of using these methods in a campaign to certify selenized yeast. Good agreement was found between the methods, which, when averaged, gave concentrations of 5482.2 +/- 101 and 3256.9 +/- 217.4 microg/g for Met and SeMet, respectively. This corresponds to a 1.68:1 Met-to-SeMet ratio in the yeast. Quantification by ID LC/MS and LC ICPMS yields the most precise sets of results with relative standard deviations in the range 0.5-1.3% (n = 6). A total selenium concentration of 2064.6 +/- 45.4 microg/g was obtained for this yeast material. The extraction efficiency and a mass balance budget were determined. Acid hydrolysis liberated 81.0% of the total selenium present. SeMet comprised 79.0% of the extracted selenium and 63.9% of the total selenium present in the yeast.
authors.affiliation: Institute for National Measurement Standards, National Research Council of Canada, Ottawa, Ontario, Canada K1A 0R9.
authors.forename: Shona
authors.initials: S
authors.lastname: McSheehy
authors.forename: Lu
authors.initials: L
authors.lastname: Yang
authors.forename: Ralph
authors.initials: R
authors.lastname: Sturgeon
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Mester
mesh_terms: D002247:Carbon Isotopes; D002853:Chromatography, Liquid / Q000379:methods*; D013058:Mass Spectrometry / Q000379:methods*; D008715:Methionine / Q000032:analysis*; D012643:Selenium / Q000032:analysis; D012645:Selenomethionine / Q000032:analysis*; D013045:Species Specificity; D015003:Yeasts / Q000737:chemistry*
chemical_list: D002247:Carbon Isotopes; D012645:Selenomethionine; D008715:Methionine; D012643:Selenium