SULFUR AND SELENIUM: NUTRIENTS, BIOACTIVE ELEMENTS, AND ANALYTICAL CHALLENGES

Authors: Harnly, James - Jim; Rodriguez, Luis; Wolf, Wayne

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/15/2004
Publication Date: 7/15/2004
Citation: Harnly, J.M., Rodriguez, L.E., Wolf, W.R. 2004. Sulfur and selenium: nutrients, bioactive elements, and analytical challenges. [abstract]. October: Paper No. P4.

Interpretive Summary:

Technical Abstract: The chemistry of sulfur (S) and selenium (Se) are inextricably linked by the similarity of their size and available oxidation states. Biologically, they are both found in essential, genetically coded amino acids (methionine, cysteine, and selenocysteine) and numerous secondary metabolites. It is this latter group, that has recently received considerable attention as a result of their alleged health promoting properties. Amino acid secondary metabolites of sulfur (glucosinolates and S-alk(en)yl-cysteine sulfoxides) and selenium (selenomethionine, Se-alk(en)yl-selenocysteines, and '-glutamyl-Se-methyl-selenocysteine), found in a variety of vegetables (most notably the Alliums and the Brassicas), have been reported to have anti-carcinogenic and anti-atherosclerotic properties. The concentration of these compounds in foods is not well known. The interaction of S and Se in biological systems, as influenced by environmental factors, is even less well known. Further research on the efficacy of S and Se containing compounds requires the development of appropriate analytical methods and databases. Analytically, S and Se are dissimilar. Selenium behaves like most metals with; it has strong electronic transitions in the ultraviolet and/or visible regions and is readily detected by atomic absorption, emission, and mass spectrometry. Conversely, sulfur behaves as a non-metal and is extremely difficult to measure. It lacks strong electronic transitions and is poorly detected by atomic absorption, emission, and mass spectrometry. Element specific detection is best accomplished by chemiluminescence or microwave excitation; techniques better suited for detection of S in the gas phase. Sulfur is usually detected as a component of small molecules using organic mass spectrometry. In recent years, the combination of liquid chromatography-mass spectrometry (LC-MS) and liquid chromatography-inductively coupled plasma-mass spectrometry (LC-ICP-MS) has become the approach of choice for separating, identifying, and quantifying organometallic compounds. The elemental detection power of the ICP-MS is excellent but identification of the parent molecule is strictly dependent on retention time. Consequently, MS is required to identify the parent compound. Both S and Se suffer from isobaric interferences and have benefitted from recent advances in collision/reaction cell technology. Analogous systems exist for gas chromatography (GC), i.e. molecular detection with MS and elemental detection using atomic emission spectrometry, pulsed flame photometric spectrometry, or ICP-MS. Gas phase separation, however, usually requires derivatization of the molecules of interest. A systematic characterization of the S and Se containing compounds in foods and biological materials is will require the combination of state-of-the-art extraction, derivatization, separation, and organic, and elemental detection technology.