Speciation analysis of selenium in garlic by two-dimensional high-performance liquid chromatography with parallel inductively coupled plasma mass spectrometric and electrospray tandem mass spectrometric detection

Speciation of selenium in garlic harvested in naturally seleniferous soil was investigated. The sample was leached with water and the aqueous extract was fractionated by preparative size-exclusion chromatography. Selenium was found in only one (low-molecular mass) fraction. The chromatographic purity of the fraction was verified by reversed-phase chromatography with inductively coupled mass spectrometric detection. Again, one major signal accounting for more than 95% of the total selenium was observed. The heartcut fraction containing this compound produced an intense peak in an electrospray mass spectrum with the selenium pattern centered at m/z 313 (Se-80). Protonated molecular ions corresponding to the four Se isotopes gave rich fragmentation patterns by collision induced dissociation that allowed the identification of the selenium species to be gamma-glutamyl-Se-methylselenocysteine without the need for an authentic standard. (C) 2000 Elsevier Science B.V. All rights reserved.