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 w as 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 purit y of the fraction was verified by reversed-phase chromatography with induct ively coupled mass spectrometric detection. Again, one major signal account ing for more than 95% of the total selenium was observed. The heartcut frac tion containing this compound produced an intense peak in an electrospray m ass spectrum with the selenium pattern centered at m/z 313 (Se-80). Protona ted molecular ions corresponding to the four Se isotopes gave rich fragment ation patterns by collision induced dissociation that allowed the identific ation 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.