No abstract

No abstract

A system for on-line measurements of trace components with concentrations as low as a few pptv has been developed on the basis of proton transfer reactions. Medical applications by means of breath analysis allow the monitoring of metabolic processes in the human body, and examples of food research include investigations of volatile organic compound (VOC) emissions from fruit, coffee and meat. Investigations of VOC emissions from decaying biomatter and on-line monitoring of the diurnal variations of VOCs in ambient air are typical examples of environmental applications.

No abstract

Abstract. Volatile organic compounds (VOCs) released from vegetation, including wound-induced VOCs, can have important effects on atmospheric chemistry. The analytical methods for measuring wound-induced VOCs, especially the hexenal family of VOCs (hexenals, hexenols, and hexenyl esters), are complicated by their chemical instability and the transient nature of their formation after leaf and stem wounding. Here we demonstrate that formation and emission of hexenal family compounds can be monitored on-line using proton-transfer-reaction mass spectrometry (PTR-MS), avoiding the need for preconcentration or chromatography. These measurements allow direct analysis of the rapid emission of the parent compound, (Z)-3-hexenal, within 1-2 s of wounding of aspen leaves and then its disappearance and the appearance of its metabolites including (E)-2-hexenal, hexenols, and hexenyl acetates. Similar results were seen in wounded beech leaves and clover. The emission of hexenal family compounds was proportional to the extent of wounding, was not dependent on light, occurred in attached or detached leaves, and was greatly enhanced as detached leaves dried out. Emission of (Z)-3-hexenal from detached drying aspen leaves averaged 500/xg C g-• (dry leaf weight). Leaf wound compounds were not emitted in a nitrogen atmosphere but were released within seconds of reintroduction of oxygen; this indicates that there are not large pools of hexenyl compounds in leaves. The PTR-MS method also allows the simultaneous detection of less abundant hexanal family VOCs including hexanal, hexanol, and hexyl acetate and VOCs formed in the light (isoprene) or during anoxia (acetaldehyde). PTR-MS may be a useful tool for the analysis of VOC emissions resulting from grazing, herbivory, and other physical damage to vegetation, from harvesting of crops, and from senescing leaves. It is clear that the hexanal and hexenal family compounds have sufficient volatility to enter the atmosphere. Arey et al. [1991, 1993] (2) where k is the rate constant for reaction (1) and t is the time the H3 O+ ions need to traverse the drift tube. PTR-MS combines chemical ionization (CI) due to ionmolecule-reactions, introduced by Munson and Field [1966], with the swarm technique of the flow-drift-tube type, invented by Ferguson and his colleagues in the early 1970s [McFarland et al., 1973]. H•O + is used as the ionizing agent and performs proton-transfer-reactions with nearly any VOC but does not react with the major gases of air (as theyIn many cases the proton-transfer reactions are nondissociative; however, in the present case, where emissions of various hexenal and hexanal family compounds were investigated, dissociation occurs during the proton transfer. Using standard hexyl and hexenyl compounds that were available commercially, we examined the fragmentation patterns of each under PTR-MS conditions that were identical to that used in leaf wound volatile analysis. The results are summarized in Table 1, (2) a, 83 (61), 57 (3), 55 (34) 143 (2) a, 99 (1), 83 (66),...