[Karl2012] "Selective measurements of isoprene and 2-methyl-3-buten-2-ol based on NO+ ionization mass spectrometry",
Atmospheric Chemistry and Physics
, vol. 12, no. 24: Copernicus GmbH, pp. 11877–11884, 2012.
Biogenic VOC emissions are often dominated by 2-methyl-1,3-butadiene (isoprene) and 2-methyl-3-buten-2-ol (232 MBO). Here we explore the possibility to selectively distinguish these species using NO+ as a primary ion in a conventional PTR-MS equipped with an SRI unit. High purity of NO+ (>90%) as a primary ion was utilized in laboratory and field experiments using a conventional PTR-TOF-MS. Isoprene is ionized via charge transfer leading to the major product ion C5H8+ (>99%) (e.g. Spanel and Smith, 1998). 232 MBO undergoes a hydroxide ion transfer reaction resulting in the major product ion channel C5H9+ (>95%) (e.g. Amelynck et al., 2005). We show that both compounds are ionized with little fragmentation (>5%) under standard operating conditions. Typical sensitivities of 11.1 ± 0.1 (isoprene) and 12.9 ± 0.1 (232 MBO) ncps ppbv−1 were achieved, which correspond to limit of detections of 18 and 15 pptv respectively for a 10 s integration time. Sensitivities decreased at higher collisional energies. Calibration experiments showed little humidity dependence. We tested the setup at a field site in Colorado dominated by ponderosa pine, a 232 MBO emitting plant species. Our measurements confirm 232 MBO as the dominant biogenic VOC at this site, exhibiting typical average daytime concentrations between 0.2–1.4 ppbv. The method is able to detect the presence of trace levels of isoprene at this field site (90–250 ppt) without any interference from 232 MBO, which would not be feasible using H3O+ ionization chemistry, and which currently also remains a challenge for other analytical techniques (e.g. gas chromatographic methods).
[Nolscher2012] "Summertime total OH reactivity measurements from boreal forest during HUMPPA-COPEC 2010",
Atmospheric Chemistry and Physics
, vol. 12, no. 17: Copernicus GmbH, pp. 8257–8270, 2012.
Ambient total OH reactivity was measured at the Finnish boreal forest station SMEAR II in Hyytiälä (Latitude 61°51' N; Longitude 24°17' E) in July and August 2010 using the Comparative Reactivity Method (CRM). The CRM – total OH reactivity method – is a direct, in-situ determination of the total loss rate of hydroxyl radicals (OH) caused by all reactive species in air. During the intensive field campaign HUMPPA-COPEC 2010 (Hyytiälä United Measurements of Photochemistry and Particles in Air – Comprehensive Organic Precursor Emission and Concentration study) the total OH reactivity was monitored both inside (18 m) and directly above the forest canopy (24 m) for the first time. The comparison between these two total OH reactivity measurements, absolute values and the temporal variation have been analyzed here. Stable boundary layer conditions during night and turbulent mixing in the daytime induced low and high short-term variability, respectively. The impact on total OH reactivity from biogenic emissions and associated photochemical products was measured under "normal" and "stressed" (i.e. prolonged high temperature) conditions. The advection of biomass burning emissions to the site caused a marked change in the total OH reactivity vertical profile. By comparing the OH reactivity contribution from individually measured compounds and the directly measured total OH reactivity, the size of any unaccounted for or "missing" sink can be deduced for various atmospheric influences. For "normal" boreal conditions a missing OH reactivity of 58%, whereas for "stressed" boreal conditions a missing OH reactivity of 89% was determined. Various sources of not quantified OH reactive species are proposed as possible explanation for the high missing OH reactivity.
[Kirsch2012] "Time-dependent aroma changes in breast milk after oral intake of a pharmacological preparation containing 1,8-cineole.",
, vol. 31, no. 5: Department of Chemistry and Pharmacy, Food Chemistry, Emil Fischer Center, University Erlangen-Nuremberg, 91052 Erlangen, Germany., pp. 682–692, Oct, 2012.
This study investigates time-dependent aroma changes in human milk after intake of an odorant-containing pharmaceutical preparation by correlating sensory evaluation with quantitative results.Human milk donors ingested 100 mg of encapsulated 1,8-cineole. 21 milk samples from 12 participants underwent sensory analysis, of which 14 samples were quantified by stable isotope dilution assay (SIDA) analysis. Furthermore, several consecutive breast milk and exhaled breath gas samples from one volunteer after intake of 1,8-cineole were analysed by proton-transfer-reaction mass spectrometry (PTR-MS) and sensory evaluation on three separate days.The emergence of the characteristic eucalyptus-like odour of 1,8-cineole in exhaled breath after capsule ingestion coincided with its transfer into milk; its presence in breath was therefore used to indicate the time at which milk should be expressed for gathering samples. Odorant transfer could not be confirmed by sensory analysis in 7 of the 21 milk samples, most likely due to disadvantageous timing of milk expression. The other 14 samples exhibited a distinct eucalyptus-like odour. Quantitative results matched these observations with <20 ?g/kg 1,8-cineole in the odourless samples and 70 to an estimated 2090 ?g/kg 1,8-cineole in the other samples.Transfer of 1,8-cineole into human milk after oral intake is time dependent and exhibits large inter and intra-individual differences.
[Benjamin2012] "Tongue pressure and oral conditions affect volatile release from liquid systems in a model mouth.",
J Agric Food Chem
, vol. 60, no. 39: Riddet Institute, Massey University , Palmerston North 4442, New Zealand. email@example.com, pp. 9918–9927, Oct, 2012.
The release of volatile organic compounds (VOCs) into the mouth cavity is an integral part of the way flavor is perceived. An in vitro model mouth with an artificial tongue was developed to measure the dynamic release of VOCs from liquid model systems [e.g., aqueous solution, oil, and oil-in-water (O/W) emulsions] under oral conditions. The release of seven selected VOCs was affected by the different polarity and vapor pressure of the compounds and their affinity to the liquid system media. Different tongue pressure patterns were applied to the liquid systems, and the release of VOCs was monitored in real time using proton transfer reaction-mass spectrometry. The release was significantly more intense for longer tongue pressure duration and was influenced by the tongue altering the sample surface area and the distribution of the VOCs. The role of saliva (artificial versus human) and the sample temperature had a significant effect on VOC release. Saliva containing mucin and a higher sample temperature enhanced the release.
[Dolgorouky2012] "Total OH reactivity measurements in Paris during the 2010 MEGAPOLI winter campaign",
Atmospheric Chemistry and Physics
, vol. 12, no. 20: Copernicus GmbH, pp. 9593–9612, 2012.
Hydroxyl radicals play a central role in the troposphere as they control the lifetime of many trace gases. Measurement of OH reactivity (OH loss rate) is important to better constrain the OH budget and also to evaluate the completeness of measured VOC budget. Total atmospheric OH reactivity was measured for the first time in an European Megacity: Paris and its surrounding areas with 12 million inhabitants, during the MEGAPOLI winter campaign 2010. The method deployed was the Comparative Reactivity Method (CRM). The measured dataset contains both measured and calculated OH reactivity from CO, NOx and VOCs measured via PTR-MS, GC-FID and GC-MS instruments. The reactivities observed in Paris covered a range from 10 s−1 to 130 s−1, indicating a large loading of chemical reactants. The present study showed that, when clean marine air masses influenced Paris, the purely local OH reactivity (20 s−1) is well explained by the measured species. Nevertheless, when there is a continental import of air masses, high levels of OH reactivity were obtained (120–130 s−1) and the missing OH reactivity measured in this case jumped to 75%. Using covariations of the missing OH reactivity to secondary inorganic species in fine aerosols, we suggest that the missing OH reactants were most likely highly oxidized compounds issued from photochemically processed air masses of anthropogenic origin.
[Danner2012] "Tracing hidden herbivores: time-resolved non-invasive analysis of belowground volatiles by proton-transfer-reaction mass spectrometry (PTR-MS).",
J Chem Ecol
, vol. 38, no. 6: Department of Ecogenomics, Institute for Water and Wetland Research (IWWR), Radboud University, PO Box 9010, 6500 GL, Nijmegen, The Netherlands. firstname.lastname@example.org, pp. 785–794, Jun, 2012.
Root herbivores are notoriously difficult to study, as they feed hidden in the soil. However, root herbivores may be traced by analyzing specific volatile organic compounds (VOCs) that are produced by damaged roots. These VOCs not only support parasitoids in the localization of their host, but also may help scientists study belowground plant-herbivore interactions. Herbivore-induced VOCs are usually analyzed by gas-chromatography mass spectrometry (GC-MS), but with this off-line method, the gases of interest need to be preconcentrated, and destructive sampling is required to assess the level of damage to the roots. In contrast to this, proton-transfer-reaction mass spectrometry (PTR-MS) is a very sensitive on-line, non-invasive method. PTR-MS already has been successfully applied to analyze VOCs produced by aboveground (infested) plant parts. In this review, we provide a brief overview of PTR-MS and illustrate how this technology can be applied to detect specific root-herbivore induced VOCs from Brassica plants. We also specify the advantages and disadvantages of PTR-MS analyses and new technological developments to overcome their limitations.
[Simpraga2012] "Understanding the link between photosynthesis, growth and emissions of biogenic volatile organic compounds (BVOCs) in beech, oak and ash",
: Ghent University, 2012.
Gas exchange between vegetation and the atmosphere is very dynamic. In addition to gases such as carbon dioxide (CO2), water vapor, oxygen, nitrogen oxides (NOx), sulphur dioxide, ammonia and ozone (O3), also biogenic volatile organic compounds (BVOCs) are exchanged between the vegetation and the atmosphere. This PhD focussed on the exchange of CO2 and BVOCs, since net photosynthesis (Pn) and BVOC emission are two plant processes important in plant functioning. Vegetation, and forests in particular, acts as a major source of BVOCs. The importance of the study lays in understanding the link between Pn, BVOC emissions and tree growth. BVOC emissions indirectly affect climate change as BVOCs are in combination with atmospheric NOx the main precursors of photochemical O3 in the troposphere, where it acts as potential greenhouse gas, damaging vegetation and affecting human respiratory organs. BVOCs are therefore dominant reactive compounds in the troposphere and important in atmospheric chemistry and climatology. Understanding tree chemistry and ecophysiology is crucial to predict future changes in the Earth’s carbon balance as well as to update BVOC inventories and improve predictions in tropospheric air chemistry. Accordingly, the main goals of the PhD were to identify and quantify the effects of temperature, drought, seasonality and vertical canopy gradients on Pn and BVOC emissions. The general methodology consisted of developing and constructing enclosure systems for gas exchange measurements indoors and outdoors, where coupling of an infra-red gas analysis (IRGA), proton transfer reaction-mass spectrometry (PTR-MS) and thermal desorption gas chromatography/mass spectrometry (TD-GC/MS) represented a major challenge. With respect to tree species, the focus was on European beech (Fagus sylvatica L.), while additionally common ash (Fraxinus excelsior L.) and northern red oak (Quercus rubra L.) were examined in Chapter 4. The trees were examined in growth room conditions, at the campus and in the Aelmoeseneie experimental forest. The main variables measured were Pn and BVOC emissions, in particular of monoterpenoids (MTs). In addition, microclimatic variables (air temperature, photosynthetic photon flux density, soil water potential, and vapor pressure deficit) and leaf characteristics (specific leaf area, leaf temperature, leaf pigments, and leaf water potentials) were measured. In the growth room experiments, stem diameter variations and chlorophyll indices were measured to explain the behavior of MT emissions by young beech trees. In the forest, the experimental tower showed to be an important facility for adequate local characterization of adult beech Pn and BVOC chemistry. Leaf level studies showed to be crucial for unraveling the mechanisms behind the emission of BVOCs. The results indicated a large variability in BVOC emission patterns of different tree species. Temperature, drought, seasonality, vertical canopy gradients differently influenced Pn and BVOC emissions (and in particular MTs), as well as their ratio. Indoors and outdoors day-time Pn, MT emissions and MT/Pn carbon ratio varied in a systematic manner following light and temperature changes. The results indicated that not only light affected Pn, MT emissions and MT/Pn ratio, but also showed a pronounced temperature effect on MT emissions (and hence on the MT/Pn carbon ratio), with an increasing exponential trend with rising air temperatures. Furthermore, during drought stress MT emissions showed an increasing-decreasing trend depending on the drought severity. Linear variable displacement transducers (LVDTs) showed to be useful for stress quantification in BVOC studies. Another notable finding was that, under severe drought stress, two PTR-MS signals diverged from each other, indicating the possible presence of BVOC species other than MT such as green leaf volatiles (GLVs). Seasonal measurements on anatomically different trees indicated a strong temperature rather than light dependency when looking at total BVOC emission trends. Beside substantial quantities of MTs released from leaves into the atmosphere, driven by light and temperature, beside non-MTs, MTs also showed to play a role in plant-insect interactions. Detected stress compounds proved infestiation-based emissions. Consequently, plant-insect relationships require additional research, identifying individual MT species using the GC/MS speciation approach and looking at their relationships with ecophysiological parameters. In conclusion, the performed indoor and outdoor studies demonstrated that Pn and BVOC emissions are strongly interrelated. Proposed hypotheses were tested and confirmed. However, many unanswered questions remain, e.g. how the distribution of individual BVOC compounds correlated with temperature and drought stress as well as along the vertical canopy gradient.
[Vesin2012] "Use of the HS-PTR-MS for online measurements of pyrethroids during indoor insecticide treatments.",
Anal Bioanal Chem
, vol. 403, no. 7: Aix-Marseille Univ, LCE-IRA, 13331 Marseille, France., pp. 1907–1921, Jun, 2012.
A high-sensitivity proton transfer reaction mass spectrometer (HS-PTR-MS) has been used to study the temporal evolution of pesticide concentrations in indoor environments. Because of the high time variability of the indoor air concentrations during household pesticide applications, the use of this online high time resolution instrument is found relevant. Four pyrethroid pesticides of the latest generation that are commonly found in electric vaporizer refills, namely, transfluthrin, empenthrin, tetramethrin, and prallethrin, were considered. A controlled pesticide generation system was settled and coupled to a HS-PTR-MS analyzer, and a calibration procedure based on the fragmentation patterns of the protonated molecules was performed. To illustrate the functionality of the method, measurements of the concentration-time profiles of transfluthrin contained in an electric vaporizer were carried out in a full-scale environmental room under air exchange rate-controlled conditions. This study demonstrates that the HS-PTR-MS technique can provide online and high time-resolved measurements of semi-volatile organic compounds such as pyrethroid insecticides.
[Ni2012] "Volatile organic compounds at swine facilities: a critical review.",
, vol. 89, no. 7: Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA. email@example.com, pp. 769–788, Oct, 2012.
Volatile organic compounds (VOCs) are regulated aerial pollutants that have environmental and health concerns. Swine operations produce and emit a complex mixture of VOCs with a wide range of molecular weights and a variety of physicochemical properties. Significant progress has been made in this area since the first experiment on VOCs at a swine facility in the early 1960s. A total of 47 research institutions in 15 North American, European, and Asian countries contributed to an increasing number of scientific publications. Nearly half of the research papers were published by U.S. institutions. Investigated major VOC sources included air inside swine barns, in headspaces of manure storages and composts, in open atmosphere above swine wastewater, and surrounding swine farms. They also included liquid swine manure and wastewater, and dusts inside and outside swine barns. Most of the sample analyses have been focusing on identification of VOC compounds and their relationship with odors. More than 500 VOCs have been identified. About 60% and 10% of the studies contributed to the quantification of VOC concentrations and emissions, respectively. The largest numbers of VOC compounds with reported concentrations in a single experimental study were 82 in air, 36 in manure, and 34 in dust samples. The relatively abundant VOC compounds that were quantified in at least two independent studies included acetic acid, butanoic acid (butyric acid), dimethyl disulfide, dimethyl sulfide, iso-valeric, p-cresol, propionic acid, skatole, trimethyl amine, and valeric acid in air. They included acetic acid, p-cresol, iso-butyric acid, butyric acid, indole, phenol, propionic acid, iso-valeric acid, and skatole in manure. In dust samples, they were acetic acid, propionic acid, butyric acid, valeric acid, p-cresol, hexanal, and decanal. Swine facility VOCs were preferentially bound to smaller-size dusts. Identification and quantification of VOCs were restricted by using instruments based on gas Chromatography (GC) and liquid chromatography (LC) with different detectors most of which require time-consuming procedures to obtain results. Various methodologies and technologies in sampling, sample preparation, and sample analysis have been used. Only four publications reported using GC based analyzers and PTR-MS (proton-transfer-reaction mass spectrometry) that allowed continuous VOC measurement. Because of this, the majority of experimental studies were only performed on limited numbers of air, manure, or dust samples. Many aerial VOCs had concentrations that were too low to be identified by the GC peaks. Although VOCs emitted from swine facilities have environmental concerns, only a few studies investigated VOC emission rates, which ranged from 3.0 to 176.5mgd(-1)kg(-1) pig at swine finishing barns and from 2.3 to 45.2gd(-1)m(-2) at manure storages. Similar to the other pollutants, spatial and temporal variations of aerial VOC concentrations and emissions existed and were significantly affected by manure management systems, barn structural designs, and ventilation rates. Scientific research in this area has been mainly driven by odor nuisance, instead of environment or health concerns. Compared with other aerial pollutants in animal agriculture, the current scientific knowledge about VOCs at swine facilities is still very limited and far from sufficient to develop reliable emission factors.
[Weise2012] "Volatile organic compounds produced by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria 85-10.",
Beilstein J Org Chem
, vol. 8: University of Rostock, Institute of Biological Sciences, Albert-Einstein-Str. 3, 18059 Rostock, Germany., pp. 579–596, 2012.
Xanthomonas campestris is a phytopathogenic bacterium and causes many diseases of agricultural relevance. Volatiles were shown to be important in inter- and intraorganismic attraction and defense reactions. Recently it became apparent that also bacteria emit a plethora of volatiles, which influence other organisms such as invertebrates, plants and fungi. As a first step to study volatile-based bacterial-plant interactions, the emission profile of Xanthomonas c. pv. vesicatoria 85-10 was determined by using GC/MS and PTR-MS techniques. More than 50 compounds were emitted by this species, the majority comprising ketones and methylketones. The structure of the dominant compound, 10-methylundecan-2-one, was assigned on the basis of its analytical data, obtained by GC/MS and verified by comparison of these data with those of a synthetic reference sample. Application of commercially available decan-2-one, undecan-2-one, dodecan-2-one, and the newly synthesized 10-methylundecan-2-one in bi-partite Petri dish bioassays revealed growth promotions in low quantities (0.01 to 10 ?mol), whereas decan-2-one at 100 ?mol caused growth inhibitions of the fungus Rhizoctonia solani. Volatile emission profiles of the bacteria were different for growth on media (nutrient broth) with or without glucose.
 "Within-plant isoprene oxidation confirmed by direct emissions of oxidation products methyl vinyl ketone and methacrolein",
Glob Change Biol
, vol. 18, pp. 973–984, Mar, 2012.
Link: http://nature.berkeley.edu/ahg/pubs/Jardine et al. 2012 GCB published.pdf
<p>Isoprene is emitted from many terrestrial plants at high rates, accounting for an estimated 1/3 of annual global volatile organic compound emissions from all anthropogenic and biogenic sources combined. Through rapid photooxidation reactions in the atmosphere, isoprene is converted to a variety of oxidized hydrocarbons, providing higher order reactants for the production of organic nitrates and tropospheric ozone, reducing the availability of oxidants for the breakdown of radiatively active trace gases such as methane, and potentially producing hygroscopic particles that act as effective cloud condensation nuclei. However, the functional basis for plant production of isoprene remains elusive. It has been hypothesized that in the cell isoprene mitigates oxidative damage during the stress-induced accumulation of reactive oxygen species (ROS), but the products of isoprene-ROS reactions in plants have not been detected. Using pyruvate-2-13C leaf and branch feeding and individual branch and whole mesocosm flux studies, we present evidence that isoprene (i) is oxidized to methyl vinyl ketone and methacrolein (iox) in leaves and that iox/i emission ratios increase with temperature, possibly due to an increase in ROS production under high temperature and light stress. In a primary rainforest in Amazonia, we inferred significant in plant isoprene oxidation (despite the strong masking effect of simultaneous atmospheric oxidation), from its influence on the vertical distribution of iox uptake fluxes, which were shifted to low isoprene emitting regions of the canopy. These observations suggest that carbon investment in isoprene production is larger than that inferred from emissions alone and that models of tropospheric chemistry and biota–chemistry–climate interactions should incorporate isoprene oxidation within both the biosphere and the atmosphere with potential implications for better understanding both the oxidizing power of the troposphere and forest response to climate change.</p>