Temperature-dependent release of volatile organic compounds of eucalypts by direct analysis in real time (DART) mass spectrometry Simin D. Maleknia 1,2,3 * , Teresa M. Vail 4 , Robert B. Cody 5 , David O. Sparkman 4 , Tina L. Bell 3,6 and Mark A. Adams 1,2,3 1 School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, NSW, Australia 2 Faculty of Agriculture, Food and Natural Resources, University of Sydney, NSW Australia 3 Bushfire Cooperative Research Centre, East Melbourne, VIC, Australia 4 Department of Chemistry, University of the Pacific, Stockton, CA, USA 5 JEOL USA, Inc., Peabody, MA, USA 6 School of Forest and Ecosystem Science, University of Melbourne, Creswick, VIC, Australia Received 3 March 2009; Revised 15 May 2009; Accepted 19 May 2009 A method is described for the rapid identification of biogenic, volatile organic compounds (VOCs) emitted by plants, including the analysis of the temperature dependence of those emissions. Direct analysis in real time (DART) enabled ionization of VOCs from stem and leaf of several eucalyptus species including E. cinerea, E. citriodora, E. nicholii and E. sideroxylon. Plant tissues were placed directly in the gap between the DART ionization source skimmer and the capillary inlet of the time- of-flight (TOF) mass spectrometer. Temperature-dependent emission of VOCs was achieved by adjusting the temperature of the helium gas into the DART ionization source at 50, 100, 200 and 300-C, which enabled direct evaporation of compounds, up to the onset of pyrolysis of plant fibres (i.e. cellulose and lignin). Accurate mass measurements facilitated by TOF mass spectrometry provided elemental compositions for the VOCs. A wide range of compounds was detected from simple organic compounds (i.e. methanol and acetone) to a series of monoterpenes (i.e. pinene, camphene, cymene, eucalyptol) common to many plant species, as well as several less abundant sesquiterpenes and flavonoids (i.e. naringenin, spathulenol, eucalyptin) with antioxidant and antimicrobial properties. The leaf and stem tissues for all four eucalypt species showed similar compounds. The relative abundances of methanol and ethanol were greater in stem wood than in leaf tissue suggesting that DART could be used to investigate the tissue-specific transport and emissions of VOCs. Copyright # 2009 John Wiley & Sons, Ltd. Volatile organic compounds (VOCs) are continually emitted from all types of vegetation, and globally contribute tera- gram (Tg ¼ 10 12 g) amounts of carbon to the biosphere each year. Biogenic VOCs incorporate a wide range of com- pounds, including highly reactive organic acids, aldehydes and esters, as well as plant-specific isoprenoids (isoprene and terpenes) with substantial impact on the chemistry of the atmosphere. The range of biogenic compounds and their concentrations are affected to a large extent by diurnal cycles (sunlight and temperature) and other environmental factors (e.g. soil moisture and nutrients). 1–3 Considerable recent attention has been directed to the identification and quantification of biogenic VOCs and their important role in atmospheric chemistry. 4–9 Mass spectrom- etry has traditionally been a tool-of-choice for studies of complex atmospheric reactions. During the past decade, proton transfer reaction mass spectrometry (PTR-MS) has been successfully applied in environmental and atmospheric research for the analysis of VOCs in real-time. 10,11 Trace level detection of atmospheric VOCs by PTR-MS is facilitated through selective proton transfer reactions with H 3 O þ (proton affinity of 166.5 kcal/mol) since the proton affinities of major components of air (N 2 and O 2 ) are less than that of water. This unique process enables direct analysis of VOCs in air at low concentrations (ppbv to pptv) without pre- concentration steps that could bias the detection of specific compounds, and we have applied PTR-MS for the analysis of VOCs of eucalypts from ambient to combustion tempera- tures. 12,13 Direct analysis in real time (DART) ion sources were introduced in 2005 and are another important development in the mass spectrometric analysis of a range of compounds in the open air from various surfaces. 14–16 DART has facilitated the trace level detection of both polar and non- polar chemicals analyzed directly from human skin, paper, plastic, fabrics, fruits and vegetables. DART ion sources use a flow of helium gas through an electrode to generate high- energy species (metastable gaseous atoms or molecules) that RAPID COMMUNICATIONS IN MASS SPECTROMETRY Rapid Commun. Mass Spectrom. 2009; 23: 2241–2246 Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rcm.4133 *Correspondence to: S. D. Maleknia, School of Biological, Earth & Environmental Sciences, The University of New South Wales, Sydney, NSW 2052, Australia. E-mail: s.maleknia@unsw.edu.au Copyright # 2009 John Wiley & Sons, Ltd.