Determination of S-methyl-, S-propyl-, and S-propenyl-L-cysteine sulfoxides by gas chromatography-mass spectrometry after tert-butyldimethylsilylation.
A gas chromatographic-mass spectrometric method for the determination of S-methyl-L-cysteine sulfoxide (1), S-propyl-L-cysteine sulfoxide (2), and S-propenyl-L-cysteine sulfoxide (3), specific marker compounds in the genus Allium, is described. The target amino acids were converted to the tert-butyldimethylsilyl derivatives. The products were silylated on the amino and carboxyl groups and on an additional oxygen atom and were separated on a nonpolar capillary column. That incorporation of three tert-butyldimethylsilyl groups had occurred was verified by mass spectrometry, which gave an m/z 302 fragment as base peak (amino acid side chain eliminated ion) and m/z 436 (1), 464 (2), or 462 (3) as major peaks (tert-butyl function eliminated ion), by electron impact ionization. The detection limits for 1 and 2 under selected ion monitoring at m/z 436 (1) and m/z 464 (2), respectively, were determined to be 0.3 and 1.8 ng per injection. To clean up the analytes from the solvent extract of onion, as a representative food material, onion, the sample solution was subjected to combined solid phase extraction. The eluate from a Sep-Pak C(18) cartridge was applied to a Bond Elut SCX cartridge (H(+) form), followed by washing with 0.1 M hydrochloric acid and elution with 0.5 M ammonia. From a simulated matrix solution containing 5% sucrose, 1 and 2 were extracted quantitatively, and the detection yield was approximately 75%. The contents of 1, 2, and 3 in commercial onion were estimated to be 0.3, 3.1, and 3.0 mg, respectively, per gram of fresh weight.
Tsuge
Kouichiro
K
National Research Institute of Police Science, 6-3-1 Kashiwanoha, Kashiwa, Chiba 277-0882, Japan.
Kataoka
Mieko
M
Seto
Yasuo
Y
D002851:Chromatography, High Pressure Liquid; D003545:Cysteine / Q000031:analogs & derivatives* / Q000032:analysis* / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D019697:Onions / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D013454:Sulfoxides / Q000032:analysis* / Q000737:chemistry
D012821:Silanes; D013454:Sulfoxides; C103256:tert-butyldimethylsilane; C008389:methiin; C028742:S-propylcysteine; D003545:Cysteine