[vonDahl2006] "Caterpillar-elicited methanol emission: a new signal in plant-herbivore interactions?",
, vol. 46, no. 6: Department of Molecular Ecology, Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Strasse 8, 07745 Jena, Germany., pp. 948–960, Jun, 2006.
Plants release into the atmosphere large quantities of volatile organic compounds (VOCs), of which methanol (MeOH), a putative waste product, is the second most abundant. Using online proton-transfer-reaction mass spectrometry (PTR-MS), we demonstrate that when Manduca sexta larvae attack Nicotiana attenuata plants, the wound-induced release of MeOH dramatically increases. The sustained MeOH emission 24 h after herbivore feeding is already substantially greater than the release of the well-characterized green-leaf VOC E-2-hexenal. Herbivore attack and treatment of puncture wounds with larval oral secretions (OS) increased the transcript accumulation and activity of leaf pectin methylesterases (PMEs), and decreased the degree of pectin methylation, as determined by (1)H-NMR; therefore, we propose that the released MeOH originates from the activation of PMEs by herbivore attack. The herbivore- and OS-elicited MeOH results not from the activity of previously characterized elicitors in OS but from a pH shift at the wound site when larval OS (pH 8.5-9.5) are introduced into the wounds during feeding. Applying MeOH to plants in quantities that mimic the herbivory-elicited release decreases the activity of the potent plant defense proteins trypsin proteinase inhibitors (TPI), and increases the performance of the attacking larvae. The pH of lepidopteran larvae regurgitants is commonly very high, and the MeOH released during feeding that is elicited by the pH change at the wound site functions as a quantitative signal that influences the outcome of the plant-herbivore interaction.
[Zavala2006] "Characterization of on-road vehicle emissions in the Mexico City Metropolitan Area using a mobile laboratory in chase and fleet average measurement modes during the MCMA-2003 field campaign",
Atmospheric Chemistry and Physics
, vol. 6, no. 12: Copernicus GmbH, pp. 5129–5142, 2006.
A mobile laboratory was used to measure on-road vehicle emission ratios during the MCMA-2003 field campaign held during the spring of 2003 in the Mexico City Metropolitan Area (MCMA). The measured emission ratios represent a sample of emissions of in-use vehicles under real world driving conditions for the MCMA. From the relative amounts of NOx and selected VOC's sampled, the results indicate that the technique is capable of differentiating among vehicle categories and fuel type in real world driving conditions. Emission ratios for NOx, NOy, NH3, H2CO, CH3CHO, and other selected volatile organic compounds (VOCs) are presented for chase sampled vehicles in the form of frequency distributions as well as estimates for the fleet averaged emissions. Our measurements of emission ratios for both CNG and gasoline powered "colectivos" (public transportation buses that are intensively used in the MCMA) indicate that – in a mole per mole basis – have significantly larger NOx and aldehydes emissions ratios as compared to other sampled vehicles in the MCMA. Similarly, ratios of selected VOCs and NOy showed a strong dependence on traffic mode. These results are compared with the vehicle emissions inventory for the MCMA, other vehicle emissions measurements in the MCMA, and measurements of on-road emissions in U.S. cities. We estimate NOx emissions as 100 600±29 200 metric tons per year for light duty gasoline vehicles in the MCMA for 2003. According to these results, annual NOx emissions estimated in the emissions inventory for this category are within the range of our estimated NOx annual emissions. Our estimates for motor vehicle emissions of benzene, toluene, formaldehyde, and acetaldehyde in the MCMA indicate these species are present in concentrations higher than previously reported. The high motor vehicle aldehyde emissions may have an impact on the photochemistry of urban areas.
[Ng2006] "Contribution of first- versus second-generation products to secondary organic aerosols formed in the oxidation of biogenic hydrocarbons.",
Environ Sci Technol
, vol. 40, no. 7: Department of Environmental Science, California Institute of Technology, Pasadena, California 91125, USA., pp. 2283–2297, Apr, 2006.
Biogenic hydrocarbons emitted by vegetation are important contributors to secondary organic aerosol (SOA), but the aerosol formation mechanisms are incompletely understood. In this study, the formation of aerosols and gas-phase products from the ozonolysis and photooxidation of a series of biogenic hydrocarbons (isoprene, 8 monoterpenes, 4 sesquiterpenes, and 3 oxygenated terpenes) are examined. By comparing aerosol growth (measured by Differential Mobility Analyzers, DMAs) and gas-phase concentrations (monitored by a Proton Transfer Reaction Mass Spectrometer, PTR-MS), we study the general mechanisms of SOA formation. Aerosol growth data are presented in terms of a "growth curve", a plot of aerosol mass formed versus the amount of hydrocarbon reacted. From the shapes of the growth curves, it is found that all the hydrocarbons studied can be classified into two groups based entirely on the number of double bonds of the hydrocarbon, regardless of the reaction systems (ozonolysis or photooxidation) and the types of hydrocarbons studied: compounds with only one double bond and compounds with more than one double bond. For compounds with only one double bond, the first oxidation step is rate-limiting, and aerosols are formed mainly from low volatility first-generation oxidation products; whereas for compounds with more than one double bond, the second oxidation step may also be rate-limiting and second-generation products contribute substantially to SOA growth. This behavior is characterized by a vertical section in the growth curve, in which continued aerosol growth is observed even after all the parent hydrocarbon is consumed.
[Biasioli2006] "Correlation of PTR-MS spectral fingerprints with sensory characterisation of flavour and odour profile of "Trentingrana" cheese",
Food quality and preference
, vol. 17, no. 1: Elsevier, pp. 63–75, 2006.
Proton transfer reaction-mass spectrometry (PTR-MS) is a relatively new technique that allows the fast and accurate detection of volatile organic compounds. The paper discusses the possibility of correlating the PTR-MS spectral fingerprint of the mixture of volatile compounds present in the head-space of 20 samples of “Trentingrana”, the variety of Grana Padano produced in Trentino (Northern Italy), with the sensory evaluation (Quantitative Descriptive Analysis) of the same samples obtained by a panel of trained judges. Only attributes related to odours (six attributes) and flavours (six attributes) are considered. Results of descriptive statistics are shown and the performances of different multivariate calibration methods (Partial Least Squares, both PLS1 and PLS2) are compared by evaluating the errors in the cross-validated estimation of the sensory attributes. PLS2 seems to give a good average description providing an overall insight of the problem but does not provide an accurate prediction of the individual sensory attributes. PLS1 analysis is more accurate and performs well in most cases but it uses several latent variables, so that the interpretation of the loadings is not straightforward. The preliminary application of Orthogonal Signal Correction filtering on PTR-MS spectra followed by PLS1 analysis results in a good estimation for most of the attributes and has the advantage to use only one or two latent variables. Comparison with other works and a tentative indication of the compounds correlated with sensory description are reported.
[Klemm2006] "Experiments on forest/atmosphere exchange: Climatology and fluxes during two summer campaigns in NE Bavaria",
, vol. 40: Elsevier, pp. 3–20, 2006.
During two summer field campaigns in 2001 and 2002, biosphere/atmosphere exchange fluxes of energy, gases, and particles were quantified in a Norway spruce forest in NE Bavaria at 775 m a.s.l. The overall goal of the BEWA campaigns was to study the influence of the emissions of reactive biogenic volatile organic compounds (BVOCs) on chemical and physical processes in the atmosphere, and an overview over the meteorological conditions, experimental frame, and the achieved results is provided. A rigorous quality assurance/quality control plan was implemented. From analysis of meteorological conditions and experimental success, golden day periods were selected for coordinated data analysis. These periods cover typical summertime conditions with various wind directions, NOx mixing ratios between 2 and 10 ppb, and O3 mixing ratios ranging between 13 and 98 ppb. Diurnal patterns of trace gas concentrations resulted from the dynamics of the boundary layer, from regional atmospheric processes (for example production of O3 in the atmosphere), and deposition. Turbulence also exhibited a diurnal pattern indicating thermal production during daytime and calm conditions during nighttime. However, in many cases, turbulence was often well developed during the nights. Horizontal advection of air masses into the trunk space occurred due to the patchiness of the forest. Nevertheless, for most conditions, the application of a one-dimensional model to describe the vertical exchange processes was appropriate. Therefore, the use of one single meteorological tower to study biosphere/atmosphere exchange is valid. Measured turbulent vertical exchange fluxes were estimated to be representative within an error of less than 25%. The results for VOC concentrations and fluxes were rather heterogeneous. Both model and measurements demonstrated that the Norway spruce trees acted as a weak source of formaldehyde.
[Tamas2006] "Factors affecting ozone removal rates in a simulated aircraft cabin environment",
, vol. 40, no. 32: Elsevier, pp. 6122–6133, 2006.
Ozone concentrations were measured concurrently inside a simulated aircraft cabin and in the airstream providing ventilation air to the cabin. Ozone decay rates were also measured after cessation of ozone injection into the supply airstream. By systematically varying the presence or absence of people, soiled T-shirts, aircraft seats and a used HEPA filter, we have been able in the course of 24 experiments to isolate the contributions of these and other factors to the removal of ozone from the cabin air. In the case of this simulated aircraft, people were responsible for almost 60% of the ozone removal occurring within the cabin and recirculation system; respiration can only have been responsible for about 4% of this removal. The aircraft seats removed about 25% of the ozone; the loaded HEPA filter, 7%; and the other surfaces, 10%. A T-shirt that had been slept in overnight removed roughly 70% as much ozone as a person, indicating the importance of skin oils in ozone removal. The presence of the used HEPA filter in the recirculated airstream reduced the perceived air quality. Over a 5-h period, the overall ozone removal rate by cabin surfaces decreased at ∼3% h−1. With people present, the measured ratio of ozone's concentration in the cabin versus that outside the cabin was 0.15–0.21, smaller than levels reported in the literature. The results reinforce the conclusion that the optimal way to reduce people's exposure to both ozone and ozone oxidation products is to efficiently remove ozone from the air supply system of an aircraft.
 "Gas-phase products and secondary aerosol yields from the ozonolysis of ten different terpenes",
Journal of Geophysical Research
, vol. 111, 2006.
<p>The ozonolyses of six monoterpenes (α-pinene, β-pinene, 3-carene, terpinolene, α-terpinene, and myrcene), two sesquiterpenes (α-humulene and β-caryophyllene), and two oxygenated terpenes (methyl chavicol and linalool) were conducted individually in Teflon chambers to examine the gas-phase oxidation product and secondary organic aerosol (SOA) yields from these reactions. Particle size distribution and number concentration were monitored and allowed for the calculation of the SOA yield from each experiment, which ranged from 1 to 54%. A proton transfer reaction mass spectrometer (PTR-MS) was used to monitor the evolution of gas-phase products, identified by their mass to charge ratio (m/z). Several gas-phase oxidation products, formaldehyde, acetaldehyde, formic acid, acetone, acetic acid, and nopinone, were identified and calibrated. Aerosol yields, and the yields of these identified and calibrated oxidation products, as well as many higher m/z oxidation products observed with the PTR-MS, varied significantly between the different parent terpene compounds. The sum of measured oxidation products in the gas and particle phase ranged from 33 to 77% of the carbon in the reacted terpenes, suggesting there are still unmeasured products from these reactions. The observations of the higher molecular weight oxidation product ions provide evidence of previously unreported compounds and their temporal evolution in the smog chamber from multistep oxidation processes. Many of the observed ions, including m/z 111 and 113, have also been observed in ambient air above a Ponderosa pine forest canopy, and our results confirm they are consistent with products from terpene + O3 reactions. Many of these products are stable on the timescale of our experiments and can therefore be monitored in field campaigns as evidence for ozone oxidative chemistry.</p>
 "Gas-phase products and secondary aerosol yields from the photooxidation of 16 different terpenes",
Journal of Geophysical Research
, vol. 111, 2006.
<p>The photooxidation of isoprene, eight monoterpenes, three oxygenated monoterpenes, and four sesquiterpenes were conducted individually at the Caltech Indoor Chamber Facility under atmospherically relevant HC:NOx ratios to monitor the time evolution and yields of SOA and gas-phase oxidation products using PTR-MS. Several oxidation products were calibrated in the PTR-MS, including formaldehyde, acetaldehyde, formic acid, acetone, acetic acid, nopinone, methacrolein + methyl vinyl ketone; other oxidation products were inferred from known fragmentation patterns, such as pinonaldehyde; and other products were identified according to their mass to charge (m/z) ratio. Numerous unidentified products were formed, and the evolution of first- and second-generation products was clearly observed. SOA yields from the different terpenes ranged from 1 to 68%, and the total gas- plus particle-phase products accounted for ∼50–100% of the reacted carbon. The carbon mass balance was poorest for the sesquiterpenes, suggesting that the observed products were underestimated or that additional products were formed but not detected by PTR-MS. Several second-generation products from isoprene photooxidation, including m/z 113, and ions corresponding to glycolaldehyde, hydroxyacetone, methylglyoxal, and hydroxycarbonyls, were detected. The detailed time series and relative yields of identified and unidentified products aid in elucidating reaction pathways and structures for the unidentified products. Many of the unidentified products from these experiments were also observed within and above the canopy of a Ponderosa pine plantation, confirming that many products of terpene oxidation can be detected in ambient air using PTR-MS, and are indicative of concurrent SOA formation.</p>
[Herndon2006] "Hydrocarbon emissions from in-use commercial aircraft during airport operations.",
Environ Sci Technol
, vol. 40, no. 14: Aerodyne Research, Inc., Billerica, Massachusetts, USA. email@example.com, pp. 4406–4413, Jul, 2006.
The emissions of selected hydrocarbons from in-use commercial aircraft at a major airport in the United States were characterized using proton-transfer reaction mass spectrometry (PTR-MS) and tunable infrared differential absorption spectroscopy (TILDAS) to probe the composition of diluted exhaust plumes downwind. The emission indices for formaldehyde, acetaldehyde, benzene, and toluene, as well as other hydrocarbon species, were determined through analysis of 45 intercepted plumes identified as being associated with specific aircraft. As would have been predicted for high bypass turbine engines, the hydrocarbon emission index was greater in idle and taxiway acceleration plumes relative to approach and takeoff plumes. The opposite was seen in total NOy emission index, which increased from idle to takeoff. Within the idle plumes sampled in this study, the median emission index for formaldehyde was 1.1 g of HCHO per kg of fuel. For the subset of hydrocarbons measured in this work, the idle emissions levels relative to formaldehyde agree well with those of previous studies. The projected total unburned hydrocarbons (UHC) deduced from the range of in-use idle plumes analyzed in this work is greater than a plausible range of engine types using the defined idle condition (7% of rated engine thrust) in the International Civil Aviation Organization (ICAO) databank reference.
 "Hygroscopicity of secondary organic aerosols formed by oxidation of cycloalkenes, monoterpenes, sesquiterpenes, and related compounds",
Atmospheric Chemistry and Physics
, vol. 6, pp. 2367–2388, Jun, 2006.
<p>A series of experiments has been conducted in the Caltech indoor smog chamber facility to investigate the water uptake properties of aerosol formed by oxidation of various organic precursors. Secondary organic aerosol (SOA) from simple and substituted cycloalkenes (C5-C8) is produced in dark ozonolysis experiments in a dry chamber (RH 5%). Biogenic SOA from monoterpenes, sesquiterpenes, and oxygenated terpenes is formed by photooxidation in a humid chamber ( 50% RH). Using the hygroscopicity tandem differential mobility analyzer (HTDMA), we measure the diameter-based hygroscopic growth factor (GF) of the SOA as a function of time and relative humidity. All SOA studied is found to be slightly hygroscopic, with smaller water uptake than that of typical inorganic aerosol substances. The aerosol water uptake increases with time early in the experiments for the cycloalkene SOA, but decreases with time for the sesquiterpene SOA. This behavior could indicate competing effects between the formation of more highly oxidized polar compounds (more hygroscopic), and formation of longer-chained oligomers (less hygroscopic). All SOA also exhibit a smooth water uptake with RH with no deliquescence or efflorescence. The water uptake curves are found to be fitted well with an empirical three-parameter functional form. The measured pure organic GF values at 85% RH are between 1.09–1.16 for SOA from ozonolysis of cycloalkenes, 1.01–1.04 for sesquiterpene photooxidation SOA, and 1.06–1.10 for the monoterpene and oxygenated terpene SOA. The GF of pure SOA (GForg) in experiments in which inorganic seed aerosol is used is determined by assuming volume-weighted water uptake (Zdanovskii-Stokes-Robinson or "ZSR" approach) and using the size-resolved organic mass fraction measured by the Aerodyne Aerosol Mass Spectrometer. Knowing the water content associated with the inorganic fraction yields GForg values. However, for each precursor, the GForg values computed from different HTDMA-classified diameters agree with each other to varying degrees. Comparing growth factors from different precursors, we find that GForg is inversely proportional to the precursor molecular weight and SOA yield, which is likely a result of the fact that higher-molecular weight precursors tend to produce larger and less hygroscopic oxidation products.</p>
[Clementschitsch2006] "Improvement of bioprocess monitoring: development of novel concepts",
Microbial Cell Factories
, vol. 5, no. 19, pp. -, 2006.
The advancement of bioprocess monitoring will play a crucial role to meet the future requirements of bioprocess technology. Major issues are the acceleration of process development to reduce the time to the market and to ensure optimal exploitation of the cell factory and further to cope with the requirements of the Process Analytical Technology initiative. Due to the enormous complexity of cellular systems and lack of appropriate sensor systems microbial production processes are still poorly understood. This holds generally true for the most microbial production processes, in particular for the recombinant protein production due to strong interaction between recombinant gene expression and host cell metabolism. Therefore, it is necessary to scrutinise the role of the different cellular compartments in the biosynthesis process in order to develop comprehensive process monitoring concepts by involving the most significant process variables and their interconnections. Although research for the development of novel sensor systems is progressing their applicability in bioprocessing is very limited with respect to on-line and in-situ measurement due to specific requirements of aseptic conditions, high number of analytes, drift, and often rather low physiological relevance. A comprehensive survey of the state of the art of bioprocess monitoring reveals that only a limited number of metabolic variables show a close correlation to the currently explored chemical/physical principles. In order to circumvent this unsatisfying situation mathematical methods are applied to uncover "hidden" information contained in the on-line data and thereby creating correlations to the multitude of highly specific biochemical off-line data. Modelling enables the continuous prediction of otherwise discrete off-line data whereby critical process states can be more easily detected. The challenging issue of this concept is to establish significant on-line and off-line data sets. In this context, online sensor systems are reviewed with respect to commercial availability in combination with the suitability of offline analytical measurement methods. In a case study, the aptitude of the concept to exploit easily available online data for prediction of complex process variables in a recombinant E. coli fed-batch cultivation aiming at the improvement of monitoring capabilities is demonstrated. In addition, the perspectives for model-based process supervision and process control are outlined.
[Aprea2006a] "In vivo monitoring of strawberry flavour release from model custards: effect of texture and oral processing",
Flavour and fragrance journal
, vol. 21, no. 1: Wiley Online Library, pp. 53–58, 2006.
The interaction of oral processing protocols and food texture on in vivo flavour release was evaluated by nose-space analysis. Nose-space analysis was carried out by proton transfer reaction mass spectrometry, and strawberry-flavoured custards were prepared with 0.1% (w/w) and 1.0% (w/w) carboxymethyl cellulose to modify the texture. Two oral processing protocols were adopted during the study; a free-chewing protocol and an imposed protocol. Twenty-one subjects participated in the study. Significant effects on in-nose flavour release were observed for the type of compound, the custard's texture, the oral processing protocol and the subjects. When people were allowed to eat as they normally do, individuals could be divided into three groups on the basis of swallowing time: first group, swallowing time <4 s; second group, swallowing time >6 s; intermediate group, t(swallow) varying (4–6 s). Within each group, different effects of the texture of the custards on in-nose flavour concentrations were observed, indicating that individual behaviour plays a considerable role in determining texture effects on flavour perception.
[Boland2006] "Influence of the texture of gelatin gels and pectin gels on strawberry flavour release and perception",
, vol. 96, no. 3: Elsevier, pp. 452–460, 2006.
The release of strawberry flavour compounds from pectin gels and gelatin gels was evaluated by instrumental and sensory analysis. Three gel textures were established based on Young’s modulus of elasticity (E) for each gel. The E of the low, medium and high rigidity gelatine and pectin gels was 181, 300 and 493 N m−2, respectively. Air/gel partition coefficients were determined by static headspace analysis. In-nose/proton transfer reaction-mass spectrometry analysis produced temporal release profiles. Sensory analysis was conducted to assess perceived odour, thickness, strawberry flavour and sweetness using magnitude estimation. The type of hydrocolloid affected static and in-nose compound concentrations significantly. The pectin gels showed lower air/gel partition coefficients than the gelatin gels, but increased flavour release. Increased gel rigidity resulted in lower air/gel partition coefficients; higher maximum concentrations of volatiles and lower release rates during in-nose analysis; decreased perception of odour, strawberry flavour and sweetness; and higher intensity ratings for thickness in sensory analysis. Consequently, both type of hydrocolloid and rigidity of the sample greatly affected flavour release and perception.
[Presto2006] "Investigation of alpha-pinene + ozone secondary organic aerosol formation at low total aerosol mass.",
Environ Sci Technol
, vol. 40, no. 11: Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA., pp. 3536–3543, Jun, 2006.
We present a method for measuring secondary organic aerosol (SOA) production at low total organic mass concentration (COA) using proton-transfer reaction mass spectrometry (PTR-MS). PTR-MS provides high time resolution measurements of gas-phase organic species and, coupled with particle measurements, allows for the determination of aerosol yield in real time. This approach facilitates the measurement of aerosol production at low COA; in fact aerosol mass fractions can be measured during alpha-pinene consumption as opposed to only at the completion of gas-phase chemistry. The high time resolution data are consistent with both the partitioning theory of Pankow (Atmos. Environ. 1994, 28,185 and 189) and the previous experimental measurements. Experiments including the effect of UV illumination and NOx reveal additional features of alpha-pinene + ozone product photochemistry and volatility. The high time resolution data also elucidate aerosol production from alpha-pinene ozonolysis at COA < 10 microg m(-3) and show that extrapolations of current partitioning models to conditions of low COA significantly underestimate SOA production under dark, low-NOx conditions. However, extrapolations of current models overestimate SOA production under illuminated, higher-NOx conditions typical of polluted regional air masses.
[Mayrhofer2006] "Microbial community related to volatile organic compound (VOC) emission in household biowaste.",
, vol. 8, no. 11: Institut fuer Mikrobiologie, Universitaet Innsbruck, Innsbruck, Austria. firstname.lastname@example.org, pp. 1960–1974, Nov, 2006.
Malodorous emissions and potentially pathogenic microorganisms which develop during domestic organic waste collection are not only a nuisance but may also pose health risks. The aim of the present study was to determine whether the presence of specific microorganisms in biowastes is directly related to the composition of the emitted volatile organic compounds (VOCs). The succession of microbial communities during 16 days of storage in organic waste collection bins was studied by denaturing gradient gel electrophoresis (DGGE) of amplified 16S ribosomal DNA in parallel with a classical cultivation and isolation approach. Approximately 60 different bacterial species and 20 different fungal species were isolated. Additionally, some bacterial species were identified through sequencing of excised DGGE bands. Proton transfer reaction mass spectrometry (PTR-MS) was used to detect VOCs over the sampling periods, and co-inertia analyses of VOC concentrations with DGGE band intensities were conducted. Positive correlations, indicating production of the respective VOC or enhancement of microbial growth, and negative correlations, indicating the use of, or microbial inhibition by the respective compound, were found for the different VOCs. Measurement of the VOC emission pattern from a pure culture of Lactococcus lactis confirmed the positive correlations for the protonated masses 89 (tentatively identified as butyric acid), 63 (tentatively identified as dimethylsulfide), 69 (likely isoprene) and 73 (likely butanone).
[Abanda-Nkpwatt2006] "Molecular interaction between Methylobacterium extorquens and seedlings: growth promotion, methanol consumption, and localization of the methanol emission site.",
J Exp Bot
, vol. 57, no. 15: Biomolecular Food Technology, Technical University of Munich, Lise-Meitner-Strasse 34, D-85354 Freising, Germany., pp. 4025–4032, 2006.
Four Methylobacterium extorquens strains were isolated from strawberry (Fragaria x ananassa cv. Elsanta) leaves, and one strain, called ME4, was tested for its ability to promote the growth of various plant seedlings. Seedling weight and shoot length of Nicotiana tabacum, Lycopersicon esculentum, Sinapis alba, and Fragaria vesca increased significantly in the presence of the pink-pigmented facultative methylotroph (PPFM), but the germination behaviour of seeds from six other plants was not affected. The cell-free supernatant of the bacterial culture stimulated germination, suggesting the production of a growth-promoting agent by the methylotroph. Methanol emitted from N. tabacum seedlings, as determined by proton-transfer-reaction mass spectrometry (PTR-MS), ranged from 0.4 to 0.7 ppbv (parts per billion by volume), while significantly lower levels (0.005 to 0.01 ppbv) of the volatile alcohol were measured when the seedlings were co-cultivated with M. extorquens ME4, demonstrating the consumption of the gaseous methanol by the bacteria. Additionally, by using cells of the methylotrophic yeast Pichia pastoris transformed with the pPICHS/GFP vector harbouring a methanol-sensitive promoter in combination with the green fluorescence protein (GFP) reporter gene, stomata were identified as the main source of the methanol emission on tobacco cotyledons. Methylobacterium extorquens strains can nourish themselves using the methanol released by the stomata and release an agent promoting the growth of the seedlings of some crop plants.
[Inomata2006a] "A novel discharge source of hydronium ions for proton transfer reaction ionization: design, characterization, and performance.",
Rapid Commun Mass Spectrom
, vol. 20, no. 6: Atmospheric Environment Division, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan. email@example.com, pp. 1025–1029, 2006.
A novel ion source based on direct current (d.c.) discharge has been developed for proton transfer reaction ionization operated at relatively high ion drift tube pressure. The shape and geometry of the ion source are designed to maximize overall ion intensity and to minimize interference from sample air. The initial performance of the technique, including speciation and intensity of reagent ions, their stability, and the impact of artifact signals, is evaluated by means of a proton transfer reaction time-of-flight mass spectrometer (PTR-TOFMS) newly built in our laboratory. Intensities of the hydronium (H(3)O(+)) ions are typically (5-7) x 10(5) counts for a 1-min integration time with a duty cycle of approximately 1%. The fluctuations of the ion signals over a period of hours are within 4%. Although the formation of artifact ions from sample air (NO(+) and O(2) (+)), which react with volatile organic compounds (VOCs) and subsequently cause fragmentation, is observed as background signals in addition to hydronium and mono- and di-hydrate H(3)O(+) ions, intensities of both NO(+) and O(2) (+) ions are only approximately 0.5% of those of H(3)O(+) ions. Using our PTR-TOFMS system at a drift tube pressure of approximately 5 Torr, the detection sensitivities are significantly improved and the detection limits for propene, acetaldehyde, acetone, isoprene, benzene, toluene, and p-xylene are estimated to be at the sub-ppbv level for 1-min integration.
[Rogers2006] "On-road measurements of volatile organic compounds in the Mexico City metropolitan area using proton transfer reaction mass spectrometry",
International Journal of Mass Spectrometry
, vol. 252, no. 1: Elsevier, pp. 26–37, 2006.
A proton transfer reaction mass spectrometer (PTR-MS) was redesigned and deployed to monitor selected hydrocarbon emissions from in-use vehicles as part of the Mexico City Metropolitan Area (MCMA) 2003 field campaign. This modified PTR-MS instrument provides the necessary time response (<2 s total cycle time) and sensitivity to monitor the rapidly changing hydrocarbon concentrations, within intercepted dilute exhaust emission plumes. Selected hydrocarbons including methanol, acetaldehyde, acetone, methyl tertiary butyl ether (MTBE), benzene and toluene were among the vehicle exhaust emission components monitored. A comparison with samples collected in canisters and analyzed by gas chromatography provides validation to the interpretation of the ion assignments and the concentrations derived using the PTR-MS. The simultaneous detection of multiple hydrocarbons in dilute vehicle exhaust plumes provides a valuable tool to study the impact of driving behavior on the exhaust gas emissions.
[Tholl2006] "Practical approaches to plant volatile analysis",
The Plant Journal
, vol. 45, no. 4: Wiley Online Library, pp. 540–560, 2006.
Plants emit volatile organic compounds (VOCs) that play important roles in their interaction with the environment and have a major impact on atmospheric chemistry. The development of static and dynamic techniques for headspace collection of volatiles in combination with gas chromatography–mass spectrometry analysis has significantly improved our understanding of the biosynthesis and ecology of plant VOCs. Advances in automated analysis of VOCs have allowed the monitoring of fast changes in VOC emissions and facilitated in vivo studies of VOC biosynthesis. This review presents an overview of methods for the analysis of plant VOCs, including their advantages and disadvantages, with a focus on the latest technical developments. It provides guidance on how to select appropriate instrumentation and protocols for biochemical, physiological and ecologically relevant applications. These include headspace analyses of plant VOCs emitted by the whole organism, organs or enzymes as well as advanced on-line analysis methods for simultaneous measurements of VOC emissions with other physiological parameters.
[Aprea2006] "Proton transfer reaction-mass spectrometry (PTR-MS) headspace analysis for rapid detection of oxidative alteration of olive oil.",
J Agric Food Chem
, vol. 54, no. 20: Agri-Food Quality Department, IASMA Research Center, Via E. Mach 1, 38010 San Michele all'Adige (TN), Italy. firstname.lastname@example.org, pp. 7635–7640, Oct, 2006.
Olive oil has been characterized by rapid proton transfer reaction-mass spectrometry (PTR-MS) headspace analysis without any concentration of the volatiles or pretreatment of the samples. Comparison of extra virgin and defective (rancid) samples, as described by a panel of sensory judges, and the monitoring of thermo-oxidation processes are discussed. Multivariate analysis of PTR-MS data has been carried out and cross-validated, providing (i) reliable classification models for extra virgin oil as opposed to defective oil and (ii) calibration models able to predict independently thermo-oxidative degradation and the corresponding peroxide value. PTR-MS fragmentation patterns of volatiles considered in this study are also reported.
[Inomata2006] "PTR-MS measurements of non-methane volatile organic compounds during an intensive field campaign at the summit of Mount Tai, China",
: June, 2006.
Owing to recent industrialization, Central East China has become a significant source of air pollutants. To examine the processes controlling the chemistry and transport of tropospheric ozone, we continuously measured non-methane volatile organic compounds (NMVOCs) as part of an intensive field campaign at Mount Tai, China, in June 2006 (MTX2006), using proton transfer reaction mass spectrometry (PTR-MS). Temporal variations of NMVOCs were recorded in mass-scan mode from m/z 17 to m/z 300 during 12–30 June 2006. More than thirty kinds of NMVOCs were detected up to m/z 160, including alkenes, aromatics, alcohols, aldehydes, and ketones. Oxygenated VOCs were the predominant NMVOCs. During the night of 12 June, we observed an episode of high NMVOCs concentrations attributed to the burning of agricultural biomass. The ΔNMVOCs/ΔCO ratios derived by PTR-MS measurements for this episode are compared to emission ratios from various types of biomass burning as reviewed by Andreae and Merlet (2001) and to ratios recently measured by PTR-MS in tropical forests (Karl et al., 2007) and at urban sites (Warneke et al., 2007).
[Maerk2006] "Quantitation of furan and methylfuran formed in different precursor systems by proton transfer reaction mass spectrometry.",
J Agric Food Chem
, vol. 54, no. 7: NestlÃ© Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland., pp. 2786–2793, Apr, 2006.
Furan has recently received attention as a possibly hazardous compound occurring in certain thermally processed foods. Previous model studies have revealed three main precursor systems producing furan upon thermal treatment, i.e., ascorbic acid, Maillard precursors, and polyunsaturated lipids. We employed proton transfer reaction mass spectrometry (PTR-MS) as an on-line monitoring technique to study furan formation. Unambiguous identification and quantitation in the headspace was achieved by PTR-MS/gas chromatography-mass spectrometry coupling. Ascorbic acid showed the highest potential to generate furan, followed by glyceryl trilinolenate. Some of the reaction samples generated methylfuran as well, such as Maillard systems containing alanine and threonine as well as lipids based on linolenic acid. The furan yields from ascorbic acid were lowered in an oxygen-free atmosphere (30%) or in the presence of reducing agents (e.g., sulfite, 60%), indicating the important role of oxidation steps in the furan formation pathway. Furthermore, already simple binary mixtures of ascorbic acid and amino acids, sugars, or lipids reduced furan by 50-95%. These data suggest that more complex reaction systems result in much lower furan amounts as compared to the individual precursors, most likely due to competing reaction pathways.
[Gross2006] "Real-time measurement of oligomeric species in secondary organic aerosol with the aerosol time-of-flight mass spectrometer",
, vol. 78, no. 7: ACS Publications, pp. 2130–2137, 2006.
[Granitto2006] "Recursive feature elimination with random forest for PTR-MS analysis of agroindustrial products",
Chemometrics and Intelligent Laboratory Systems
, vol. 83, no. 2: Elsevier, pp. 83–90, 2006.
In this paper we apply the recently introduced Random Forest-Recursive Feature Elimination (RF-RFE) algorithm to the identification of relevant features in the spectra produced by Proton Transfer Reaction-Mass Spectrometry (PTR-MS) analysis of agroindustrial products. The method is compared with the more traditional Support Vector Machine-Recursive Feature Elimination (SVM-RFE), extended to allow multiclass problems, and with a baseline method based on the Kruskal–Wallis statistic (KWS). In particular, we apply all selection methods to the discrimination of nine varieties of strawberries and six varieties of typical cheeses from Trentino Province, North Italy. Using replicated experiments we estimate unbiased generalization errors. Our results show that RF-RFE outperforms SVM-RFE and KWS on the task of finding small subsets of features with high discrimination levels on PTR-MS data sets. We also show how selection probabilities and features co-occurrence can be used to highlight the most relevant features for discrimination.
[Graus2006] "A relaxed-eddy-accumulation method for the measurement of isoprenoid canopy-fluxes using an online gas-chromatographic technique and PTR-MS simultaneously",
, vol. 40: Elsevier, pp. 43–54, 2006.
A relaxed-eddy-accumulation set-up using an online gas-chromatographic technique and proton-transfer-reaction mass spectrometry was applied to determine isoprenoid fluxes above a Norway spruce forest in July 2001/2002. The system was quality assured and its suitability for determination of canopy fluxes of isoprenoids was demonstrated. Flux measurements of oxygenated hydrocarbons failed the data quality check due to artefacts presumably arising from line and ozone-scrubber effects. Observations of turbulent fluxes of isoprenoids during the two field experiments show good agreements with primary flux data derived from enclosure measurements and modelling results using a canopy-chemistry emission model (CACHE).