Does the novel fast-GC coupled with PTR-TOF-MS allow a significant advancement in detecting VOC emissions from plants?

Most plants produce and emit a wide blend of biogenic volatile organic compounds (BVOCs). Among them, many isoprenoids exhibit a high atmospheric reactivity toward OH radicals and ozone. In the last few years, Proton Transfer Reaction-Mass Spectrometry (PTR-MS) has been widely used in both field and laboratory determination of BVOCs, complementing the traditional methods using gas chromatography-mass spectrometry (GC-MS) for their identification in air and emission sources. This technical note reports a number of experiments carried out with a PTR- (Time-of-Flight) TOF-MS equipped with a prototype fast-GC system, allowing a fast separation of those isobaric isoprenoid compounds that cannot be identified by a direct PTR-TOF-MS analysis. The potential of this fast-GC system to adequately complement the information provided by PTR-TOF-MS was investigated by using the BVOC emissions of Quercus ilex and Eucalyptus camaldulensis as reliable testing systems, due to the different blend of isoprenoid compounds emitted and the different dependence of their emission from environmental parameters. While the oak species is a strong monoterpene emitter, the eucalyptus used is one of the few plant species emitting both isoprene and monoterpenes. The performances provided by the type of fast-GC used in the new PTR-TOF-MS instrument were also compared with those afforded by conven- tional GC-MS methods. The results obtained in this investigation showed that this new instrument is indeed a quick and handy tool to determine the contribution of isoprene and eucalyptol to m/z 69.070 and monoterpenes and (Z)-3-hexenal to m/z 81.070, integrating well the on-line information provided by PTR-TOF-MS. However, some limitations emerged in the instrument as compared to traditional GC-MS, which can only be solved by implementing the injection and separation processes.