Abstract:

A surface desorption atomospheric pressure chemical ionization mass spectrometry(SDAPCI-MS) method was employed to directly fingerprint 3 condiment vegetables including leek, onion, garlic with neither sample pre-treatment nor toxic chemical contamination. Identification of the molecular structure of desired ions was demonstrated by tandem mass spectrometry(MS/MS). The results show that the main components in chemical fingerprint spectrum of leek are 2-methyl-2-pentenal, methyl methanethiosulfinate, methyl allylthiosulfinate etc., among which both methyl methanethiosulfinate and methyl allylthiosulfinate give a relatively strong signal of M+H2O·+. Intact onion bulb shows so few signals in the mass spectrum that only initial ions caused by corona discharge, such as H3O+(OH), and O+2, are detected. On the other hand, dissected onion bulb gives contrastively increased mass spectrum signals, namely, S-propentyl sulphinate, propyl allylthiosulfinate and propyl propylthiosulfinate. While allyl allylthiosulfinate is detected as the main volatiles of intact garlic bulb, dissected garlic bulb mainly gives S-propentyl sulphinate. Some other signals of interested, such as methyl methanethiosulfinate, methyl allylthiosulfinate from leek, S-propentyl sulphinate from onion and allyl allylthiosulfinate from garlic were structurally identified by tandem mass spectrometry(MS/MS). As the experimental findings shows, SDAPCIMS technique is qualified for rapid non invasive analysis without sample manipulation prior to experiment, and provides practical and potential application in non-destructive testing and quality control for food.

Key words: Surface desorption atomospheric pressure chemical ionization mass spectrometry, condiment vegetable, chemical fingerprinting, rapid analysis