Wolf W R, Zainal H, Yager B
Food Composition Laboratory, BHNRC, ARS, USDA, Beltsville, MD 20705, USA.
Fresenius J Anal Chem. 2001 Jun;370(2-3):286-90. doi: 10.1007/s002160100829.
Selenium has been identified as an antioxidant of importance in the diet. Accurate determination of its chemical forms depends on the availability of suitable reference materials (RMs). Two candidate reference materials for determination of selenomethionine (Semet) in food-related materials, a standard wheat gluten sample (NIST RM 8418 Wheat Gluten) and a commercial selenium enriched yeast, have been examined by use of a gas chromatography-isotope dilution mass spectrometry (IDMS) procedure, after treatment of the matrix with 0.1 mol L(-1) hydrochloric acid containing stannous chloride, addition of CNBr, and extraction with chloroform. This procedure results in cleavage of the CH3Se group to form volatile CH3SeCN. Addition of isotopically enriched 74Semet to an analytical sample enables estimation of the naturally occurring protein-bound 80Semet by IDMS without a protein-digestion process. We found that the Wheat Gluten RM contains a significant amount of Semet as a portion of its assigned value of 2.58 microg Se(total g(-1). Commercial selenium yeast tablets are labeled as containing an elevated level of "organic selenium", usually as Semet. The sample we investigated contained 210 microg Se(total) g(-1) sample as determined separately by IDMS, measuring elemental selenium after digestion. 73% of this total (153 +/- 21 microg Se(semet) g(-1); n = 23) was present as Semet. Thus, these two materials contain significant amounts of their total selenium content as Semet and would be good candidates for further study and characterization as reference materials for determining this important food component. The CNBr reaction used will also enable the determination of Se-(methyl)selenocysteine, the biological role of which is of recent interest. In addition to matrix RMs for Semet, it is important to have standard materials of the pure substance. We have examined a sample of a candidate standard material of selenomethionine being prepared by the USP. It was confirmed that this material is pure selenomethionine.
硒已被确定为饮食中一种重要的抗氧化剂。其化学形态的准确测定取决于合适的参考物质（RM）的可用性。通过气相色谱 - 同位素稀释质谱法（IDMS）程序，在基质用含氯化亚锡的0.1 mol L⁻¹盐酸处理、加入溴化氰并用氯仿萃取后，对两种用于测定食品相关材料中硒代蛋氨酸（Semet）的候选参考物质进行了检测，这两种物质分别是标准小麦面筋样品（NIST RM 8418小麦面筋）和一种商业富硒酵母。该程序导致CH₃Se基团裂解形成挥发性的CH₃SeCN。向分析样品中添加同位素富集的⁷⁴Semet，无需蛋白质消化过程即可通过IDMS估算天然存在的蛋白质结合型⁸⁰Semet。我们发现小麦面筋参考物质在其指定值2.58 μg Se（总 g⁻¹）中含有大量的Semet。商业硒酵母片被标记为含有高水平的“有机硒”，通常为Semet。我们通过IDMS单独测定消化后的元素硒，所研究的样品含有210 μg Se（总）g⁻¹样品。其中73%（153±21 μg Se（semet）g⁻¹；n = 23）以Semet形式存在。因此，这两种物质的总硒含量中有大量以Semet形式存在，作为测定这种重要食品成分的参考物质，它们将是进一步研究和表征的良好候选物。所使用的溴化氰反应还将能够测定硒 - （甲基）硒代半胱氨酸，其生物学作用最近受到关注。除了Semet的基质参考物质外，拥有纯物质的标准物质也很重要。我们检测了美国药典正在制备的一种硒代蛋氨酸候选标准物质的样品。已确认该物质为纯硒代蛋氨酸。
