[Demarcke2009] "Laboratory studies in support of the detection of sesquiterpenes by proton-transfer-reaction-mass-spectrometry",
International Journal of Mass Spectrometry
, vol. 279, no. 2: Elsevier, pp. 156–162, 2009.
The effects of the ratio of the electric field strength to the buffer gas number density (E/N) in the drift tube of a proton transfer reaction mass spectrometer on the product ion distributions of the sesquiterpenes β-caryophyllene, α-humulene, α-cedrene and longifolene have been investigated.Chemical ionization of the sesquiterpenes resulted in important fragmentation of the nascent excited ion/molecule complex at the highest E/N values. The most important fragment ions were common to all sesquiterpenes and therefore cannot be used as fingerprints for specific isomers. The yield of the protonated molecule increased on average by a factor 1.6 by decreasing E/N from 140 to 80 Td. Taking into account the influence of E/N on the reaction time and on the reactant ion mobility, it is estimated that this decrease in E/N may lead to an overall increase in the PTR-MS detection sensitivity of sesquiterpenes (based on the ion signal at m/z 205) by a factor 3.5.Product ion distributions of α-cedrene and longifolene have also been determined at different water vapour pressures. No substantial influence of the water vapour pressure on the product ion yields was observed, which is an advantage when quantifying sesquiterpenes by PTR-MS in samples of varying relative humidity.
 "Large emissions of sesquiterpenes and methyl chavicol quantified from branch enclosure measurements",
, vol. 43, pp. 389–401, Jan, 2009.
<p>Multiple field studies have suggested chemistry within a forest canopy is poorly understood due to inadequate detection and quantification of reactive biogenic emissions, such as terpenes. To measure emission rates of terpenes at Blodgett Forest, a coniferous forest in the Sierra Nevada mountains of California, we placed enclosures over branches of the dominant species at the site – Ponderosa pine, manzanita, and ceanothus – in the summer of 2005. Zero air, with ambient CO2 concentrations, flowed through the chamber system and volatile organic compound (VOC) emission measurements were made by proton transfer reaction mass spectrometry (PTR-MS), solid phase microextraction (SPME) on fibers followed by direct injection into a gas chromatograph with an ion trap mass spectrometer (GC-ITMS), and by in situ GC with a flame ionization detector (GC-FID). We show that previously undetected sesquiterpenes and methyl chavicol significantly contribute to the total reactive biogenic emission profile from this field site.</p>
[Jordan2009] "Long-term study of VOCs measured with PTR-MS at a rural site in New Hampshire with urban influences",
Atmospheric Chemistry and Physics
, vol. 9, no. 14: Copernicus GmbH, pp. 4677–4697, 2009.
A long-term, high time-resolution volatile organic compound (VOC) data set from a ground site that experiences urban, rural, and marine influences in the Northeastern United States is presented. A proton-transfer-reaction mass spectrometer (PTR-MS) was used to quantify 15 VOCs: a marine tracer dimethyl sulfide (DMS), a biomass burning tracer acetonitrile, biogenic compounds (monoterpenes, isoprene), oxygenated VOCs (OVOCs: methyl vinyl ketone (MVK) plus methacrolein (MACR), methanol, acetone, methyl ethyl ketone (MEK), acetaldehyde, and acetic acid), and aromatic compounds (benzene, toluene, C8 and C9 aromatics). Time series, overall and seasonal medians, with 10th and 90th percentiles, seasonal mean diurnal profiles, and inter-annual comparisons of mean summer and winter diurnal profiles are shown. Methanol and acetone exhibit the highest overall median mixing ratios 1.44 and 1.02 ppbv, respectively. Comparing the mean diurnal profiles of less well understood compounds (e.g., MEK) with better known compounds (e.g., isoprene, monoterpenes, and MVK + MACR) that undergo various controls on their atmospheric mixing ratios provides insight into possible sources of the lesser known compounds. The constant diurnal value of 0.7 for the toluene:benzene ratio in winter, may possibly indicate the influence of wood-based heating systems in this region. Methanol exhibits an initial early morning release in summer unlike any other OVOC (or isoprene) and a dramatic late afternoon mixing ratio increase in spring. Although several of the OVOCs appear to have biogenic sources, differences in features observed between isoprene, methanol, acetone, acetaldehyde, and MEK suggest they are produced or emitted in unique ways.