Possible interest of various sample transfer techniques for fast gas chromatography-mass spectrometric analysis of true onion volatiles

We improved CC-MS analysis of onion volatiles by comparing organic solvent partition with solid-phase microextraction (SPME) following cryo-trapping i solation and by comparing the same extraction methods on direct onion juice . Cryotrapping produces very small quantities of volatiles and therefore is not a suitable extraction method for CC-MS analysis. We confirm that SPME accelerates the degradation of labile thiosulfinates but the lacrymatory fa ctor remains intact. The identification of Allium thiosulfinates is only ob tained on juice extracted by diethyl ether using a fast CC-MS analysis on a 10 m X 0.3 mm column of 4 mum coating, with routine splitless injection. T he lacrymatory factor is best analysed directly on fresh onion juice by SPM E with the same chromatographic conditions. To characterise and to quantify all the true onion volatiles, we propose to analyse the same sample by suc cessive SPME-GC-MS and solvent extraction-CC-MS. (C) 2000 Elsevier Science B.V. All rights reserved.