10.1021/jf304444s.s001 Nigel I. Joyce Nigel I. Joyce Colin C. Eady Colin C. Eady Patrick Silcock Patrick Silcock Nigel B. Perry Nigel B. Perry John W. van Klink John W. van Klink Fast Phenotyping of LFS-Silenced (Tearless) Onions by Desorption Electrospray Ionization Mass Spectrometry (DESI-MS) American Chemical Society 2013 lachrymatory factor synthase sulfenic acid condensates proton transfer reaction desorption electrospray ionization PTR MS tearless onions sampling LFS Allium concentration LF variety Desorption Electrospray Ionization Mass Spectrometry dipropyl disulfide 12 DESI 2013-02-20 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Fast_Phenotyping_of_LFS_Silenced_Tearless_Onions_by_Desorption_Electrospray_Ionization_Mass_Spectrometry_DESI_MS_/2441647 Fast MS techniques have been applied to the analysis of sulfur volatiles in Allium species and varieties to distinguish phenotypes. Headspace sampling by proton transfer reaction (PTR) MS and surface sampling by desorption electrospray ionization (DESI) MS were used to distinguish lachrymatory factor synthase (LFS)-silenced (tearless; LFS−) onions from normal, LFS-active (tear-inducing; LFS+), onions. PTR-MS showed lower concentrations of the lachrymatory factor (LF, <b>3</b>) and dipropyl disulfide <b>12</b> from tearless onions. DESI-MS of the tearless onions confirmed the decreased LF <b>3</b> and revealed much higher concentrations of the sulfenic acid condensates. Using DESI-MS with MS<sup>2</sup> could distinguish zwiebelane ions from thiosulfinate ions. DESI-MS gave reliable fast phenotyping of LFS+ versus LFS– onions by simply scratching leaves and recording the extractable ions for <0.5 min. DESI-MS leaf compound profiles also allowed the rapid distinction of a variety of <i>Allium</i> cultivars to aid plant breeding selections.