Negative-ion CIMS: analysis of volatile leaf wound compounds including HCN

Abstract

Chemical-ionization mass spectrometry (CIMS) using flow-reactor mass spectrometers has flourished as a sensitive, on-line method of analyzing trace volatile organic compounds (VOCs) in air. In this work, the OH− anion is explored as the ionizing reagent in a flowing-afterglow selected ion flow tube (FA-SIFT) instrument for its utility in detecting VOCs and HCN released by cut and wounded plant material. Reaction rate coefficients and products for reactions between OH− anion and 17 plant VOCs and some structural isomers are reported. These results are also compared to reactions between H3O+ and these same VOCs. Fragmentation products from collision-induced dissociation (CID) of the [M−1]− anion of each species are also given to aid in ion identification. H/D exchange was successfully used to distinguish ionized aldehyde/ketone products that are structural isomers for two different isomeric aldehyde/ketone pairs. Simultaneous emissions of acetone, butanone, and HCN were observed from several plants and the emissions of acetone and butanone were confirmed from one plant using H/D exchange. The utility of this technique as a screening tool for cyanogenesis in plants is discussed.