[Andersen2012] "Minimisation of artefact formation of dimethyl disulphide during sampling and analysis of methanethiol in air using solid sorbent materials.",
J Chromatogr A
, vol. 1245: Applied Plasma Physics AS, Bedriftsveien 25, PO Box 584, 4305 Sandnes, Norway., pp. 24–31, Jul, 2012.
Methanethiol (MT) is a potent odorant that can be difficult to measure due to its high volatility and reactivity; it easily reacts to form dimethyl disulphide (DMDS) during sampling and/or analysis. This paper focuses on finding an optimal method for sampling and measuring MT with minimum artefact formation using sorbent materials and a thermal desorption-gas chromatography-mass spectrometry method (TD-GC-MS). Experiments were conducted to identify suitable sorbent materials and tubes for analysis. Breakthrough, desorption rate, the effects of storage and desorption temperatures were investigated and different drying methods were established with respect to quantitative sampling and formation of DMDS. Proton-transfer-reaction mass spectrometry (PTR-MS) was used in the development of the method and was an especially useful tool for determination of breakthrough. The results show that glass tubes packed with silica gel for pre-concentration of MT before analysis with TD-GC-MS give the best results. In addition, a combination of Tenax TA and carbonised molecular sieve or Tenax TA cooled to 0 °C gives acceptable results. 80 °C was found to be the optimal desorption temperature. For all the sampling methods tested, storage conditions were observed to be very critical for transformation of MT. Room temperature storage should be limited to few minutes and, in general, tubes should be kept at 0Â°C or lower during storage.
[King2012] "A modeling-based evaluation of isothermal rebreathing for breath gas analyses of highly soluble volatile organic compounds",
Journal of breath research
, vol. 6, no. 1: IOP Publishing, pp. 016005, 2012.
Isothermal rebreathing has been proposed as an experimental technique for estimating the alveolar levels of hydrophilic volatile organic compounds (VOCs) in exhaled breath. Using the prototypic test compounds acetone and methanol, we demonstrate that the end-tidal breath profiles of such substances during isothermal rebreathing show a characteristic increase that contradicts the conventional pulmonary inert gas elimination theory due to Farhi. On the other hand, these profiles can reliably be captured by virtue of a previously developed mathematical model for the general exhalation kinetics of highly soluble, blood-borne VOCs, which explicitly takes into account airway gas exchange as a major determinant of the observable breath output. This model allows for a mechanistic analysis of various rebreathing protocols suggested in the literature. In particular, it predicts that the end-exhaled levels of acetone and methanol measured during free tidal breathing will underestimate the underlying alveolar concentration by a factor of up to 1.5. Moreover, it clarifies the discrepancies between in vitro and in vivo blood–breath ratios of hydrophilic VOCs and yields further quantitative insights into the physiological components of isothermal rebreathing and highly soluble gas exchange in general.
[Jordan2012] "Monitoring and Quantifying Toxic Industrial Compounds (TICs) with Proton with Proton-Transfer-Reaction Mass Spectrometry (PTR Reaction Mass Spectrometry (PTR-MS)",
: IONICON Analytik, 2012.
[Papurello2012] "Monitoring of volatile compound emissions during dry anaerobic digestion of the Organic Fraction of Municipal Solid Waste by Proton Transfer Reaction Time-of-Flight Mass Spectrometry.",
, vol. 126: Fondazione Edmund Mach, Biomass and Renewable Energy Unit, Via E. Mach 1, 38010 San Michele a/A, Italy., pp. 254–265, Dec, 2012.
Volatile Organic Compounds (VOCs) formed during anaerobic digestion of aerobically pre-treated Organic Fraction of Municipal Solid Waste (OFMSW), have been monitored over a 30 day period by a direct injection mass spectrometric technique: Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS). Most of the tentatively identified compounds exhibited a double-peaked emission pattern which is probably the combined result from the volatilization or oxidation of the biomass-inherited organic compounds and the microbial degradation of organic substrates. Of the sulfur compounds, hydrogen sulfide had the highest accumulative production. Alkylthiols were the predominant sulfur organic compounds, reaching their maximum levels during the last stage of the process. H(2)S formation seems to be influenced by the metabolic reactions that the sulfur organic compounds undergo, such as a methanogenesis induced mechanism i.e. an amino acid degradation/sulfate reduction. Comparison of different batches indicates that PTR-ToF-MS is a suitable tool providing information for rapid in situ bioprocess monitoring.
[Maerk2012] "More than one order of magnitude higher sensitivities with Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry",
: IONICON Analytik, 2012.
[Schausberger2012] "Mycorrhiza changes plant volatiles to attract spider mite enemies",
, vol. 26, no. 2: Wiley Online Library, pp. 441–449, 2012.
1. Indirect induced plant defence via emission of herbivore-induced plant volatiles (HIPV) to recruit natural enemies of herbivores is a ubiquitous phenomenon, but whether and how emission of above-ground HIPVs is adaptively modulated by below-ground mutualistic micro-organisms is unknown. 2. We investigated the effects of the mycorrhizal fungus Glomus mosseae on chemical composition of HIPVs emitted by bean plants Phaseolus vulgaris attacked by spider mites, Tetranychus urticae, using proton-transfer mass spectrometry, and attraction of the spider mites’ natural enemy, the predatory mite Phytoseiulus persimilis, to these HIPVs using a Y-tube olfactometer. 3. Mycorrhiza significantly changed the HIPV composition. Most notably, it increased the emission of β-ocimene and β-caryophyllene, two compounds synthesized de novo upon spider mite attack. The constitutively emitted methyl salicylate was increased by spider mite infestation but decreased by mycorrhiza. 4. The predators responded strongly to HIPVs emitted by plants infested for 6 days and preferred HIPVs of mycorrhizal plants to those of non-mycorrhizal plants. In contrast, they were less responsive and indiscriminative to mycorrhization when exposed to volatiles emitted by non-infested plants and plants infested by spider mites for 1 or 3 days. 5. Our study provides a key example of an adaptive indirect HIPV-mediated interaction of a below-ground micro-organism with an above-ground carnivore.
[Nolscher2012a] "A new method for total OH reactivity measurements using a fast Gas Chromatographic Photo-Ionization Detector (GC-PID)",
Atmospheric Measurement Techniques Discussions
, vol. 5, no. 3: Copernicus GmbH, pp. 3575–3609, 2012.
The primary and most important oxidant in the atmosphere is the hydroxyl radical (OH). Currently OH sinks, particularly gas phase reactions, are poorly constrained. One way to characterize the overall sink of OH is to measure directly the ambient loss rate of OH, the total OH reactivity. To date direct measurements of total OH reactivity have been either performed using a Laser Induced Fluorescence (LIF) system ("pump-and-probe" or "flow reactor") or the Comparative Reactivity Method (CRM) with a Proton Transfer Reaction Mass Spectrometer (PTR-MS). Both techniques require large, complex and expensive detection systems. This study presents a feasibility assessment for CRM total OH reactivity measurements using a new detector, a Gas Chromatographic Photo-Ionization Detector (GC-PID). Such a system is smaller, more portable, less power consuming and less expensive than other total OH reactivity measurement techniques. Total OH reactivity is measured by the CRM using a competitive reaction between a reagent (here pyrrole) with OH alone and in the presence of atmospheric reactive molecules. The new CRM method for total OH reactivity has been tested with parallel measurements of the GC-PID and the previously validated PTR-MS as detector for the reagent pyrrole during laboratory experiments, plant chamber and boreal field studies. Excellent agreement of both detectors was found when the GC-PID was operated under optimum conditions. Time resolution (60–70 s), sensitivity (LOD 3–6 s−1) and overall uncertainty (25% in optimum conditions) for total OH reactivity were equivalent to PTR-MS based total OH reactivity measurements. One drawback of the GC-PID system was the steady loss of sensitivity and accuracy during intensive measurements lasting several weeks, and a possible toluene interference. Generally, the GC-PID system has been shown to produce closely comparable results to the PTR-MS and thus in suitable environments (e.g. forests) it presents a viably economical alternative for groups interested in total OH reactivity observations.
 "OH clock determination by proton transfer reaction mass spectrometry at an environmental chamber",
Atmos. Meas. Tech.
, vol. 5, pp. 647â€“656, Mar, 2012.
<p>The hydroxyl free radical (OH) is the major oxidizing species in the lower atmosphere. Measuring the OH concentration is generally difficult and involves elaborate, expensive, custom-made experimental setups. Thus other more economical techniques, capable of determining OH concentrations at environmental chambers, would be valuable. This work is based on an indirect method of OH concentration measurement, by monitoring an appropriate OH tracer by proton transfer reaction mass spectrometry (PTR-MS). 3-pentanol, 3-pentanone and pinonaldehyde (PA) were used as OH tracers in α-pinene (AP) secondary organic aerosol (SOA) aging studies. In addition we tested butanol-d9 as a potential "universal" OH tracer and determined its reaction rate constant with OH: kbutanol-d9 = 3.4(±0.88) × 10−12 cm3 molecule−1 s−1. In order to make the chamber studies more comparable among each other as well as to atmospheric measurements we suggest the use of a chemical (time) dimension: the OH clock, which corresponds to the integrated OH concentration over time.</p>
[Sinha2012] "OH reactivity measurements in a coastal location in Southwestern Spain during DOMINO",
Atmospheric Chemistry and Physics Discussions
, vol. 12, no. 2: Copernicus GmbH, pp. 4979–5014, 2012.
In this study air masses are characterized in terms of their total OH reactivity which is a robust measure of the "reactive air pollutant loading". The measurements were performed during the DOMINO campaign (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) held from 21 November 2008 to 8 December 2008 at the Atmospheric Sounding Station – El Arenosillo (37.1° N–6.7° W, 40 m a.s.l.). The site was frequently impacted by marine air masses (arriving at the site from the southerly sector) and air masses from the cities of Huelva (located NW of the site), Seville and Madrid (located NNE of the site). OH reactivity values showed strong wind sector dependence. North eastern "continental" air masses were characterized by the highest OH reactivities (average: 31.4 ± 4.5 s−1; range of average diel values: 21.3–40.5 −1), followed by north western "industrial" air masses (average: 13.8 ± 4.4 s−1; range of average diel values: 7–23.4 s−1) and marine air masses (average: 6.3 ± 6.6 s−1; range of average diel values: below detection limit −21.7 s−1), respectively. The average OH reactivity for the entire campaign period was 18 s−1 and no pronounced variation was discernible in the diel profiles with the exception of relatively high values from 09:00 to 11:00 UTC on occasions when air masses arrived from the north western and southern wind sectors. The measured OH reactivity was used to constrain both diel instantaneous ozone production potential rates and regimes. Gross ozone production rates at the site were generally limited by the availability of NOx with peak values of around 20 ppbV O3 h−1. Using the OH reactivity based approach, derived ozone production rates indicate that if NOx would no longer be the limiting factor in air masses arriving from the continental north eastern sector, peak ozone production rates could double. We suggest that the new combined approach of in-situ fast measurements of OH reactivity, nitrogen oxides and peroxy radicals for constraining instantaneous ozone production rates, could significantly improve analyses of upwind point sources and their impact on regional ozone levels.
[Crespo2012] "On-line detection of root-induced volatiles in Brassica nigra plants infested with Delia radicum L. root fly larvae.",
, vol. 84: Life Science Trace Gas Facility, Institute of Molecules and Materials (IMM), Radboud University Nijmegen, Nijmegen, The Netherlands., pp. 68–77, Dec, 2012.
Plants emit various volatile organic compounds (VOCs) upon herbivore attack. These VOC emissions often show temporal dynamics which may influence the behavior of natural enemies using these volatiles as cues. This study analyzes on-line VOC emissions by roots of Brassica nigra plants under attack by cabbage root fly larvae, Delia radicum. Root emitted VOCs were detected using Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and Gas Chromatography-Mass Spectrometry (GC-MS). These analyses showed that several sulfur containing compounds, such as methanethiol, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and glucosinolate breakdown products, such as thiocyanates (TC) and isothiocyanates (ITC), were emitted by the roots in response to infestation. The emissions were subdivided into early responses, emerging within 1-6 h after infestation, and late responses, evolving only after 6-12 h. The marker for rapid responses was detected at m/z 60. The ion detected at m/z 60 was identified as thiocyanic acid, which is also a prominent fragment in some TC or ITC spectra. The emission of m/z 60 stopped when the larvae had pupated, which makes it an excellent indicator for actively feeding larvae. Methanethiol, DMS and DMDS levels increased much later in infested roots, indicating that activation of enzymes or genes involved in the production of these compounds may be required. Earlier studies have shown that both early and late responses can play a role in tritrophic interactions associated with Brassica species. Moreover, the identification of these root induced responses will help to design non-invasive analytical procedures to assess root infestations.
[Wieland2012] "Online monitoring of coffee roasting by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS): towards a real-time process control for a consistent roast profile",
Analytical and bioanalytical chemistry
, vol. 402, no. 8: Springer, pp. 2531–2543, 2012.
A real-time automated process control tool for coffee roasting is presented to consistently and accurately achieve a targeted roast degree. It is based on the online monitoring of volatile organic compounds (VOC) in the off-gas of a drum roaster by proton transfer reaction time-of-flight mass spectrometry at a high time (1 Hz) and mass resolution (5,500 m/Δm at full width at half-maximum) and high sensitivity (better than parts per billion by volume). Forty-two roasting experiments were performed with the drum roaster being operated either on a low, medium or high hot-air inlet temperature (= energy input) and the coffee (Arabica from Antigua, Guatemala) being roasted to low, medium or dark roast degrees. A principal component analysis (PCA) discriminated, for each one of the three hot-air inlet temperatures, the roast degree with a resolution of better than ±1 Colorette. The 3D space of the three first principal components was defined based on 23 mass spectral profiles of VOCs and their roast degree at the end point of roasting. This provided a very detailed picture of the evolution of the roasting process and allowed establishment of a predictive model that projects the online-monitored VOC profile of the roaster off-gas in real time onto the PCA space defined by the calibration process and, ultimately, to control the coffee roasting process so as to achieve a target roast degree and a consistent roasting.
[Feilberg2012] "Optimization of Biological Air Filters for Livestock Production Facilities",
International conference on environmental odour monitoring and control
[Hansen2012b] "Prediction of odor from pig production based on chemical odorants.",
J Environ Qual
, vol. 41, no. 2: Department of Engineering, Aarhus Uninversity, Denmark. email@example.com, pp. 436–443, 2012.
The present work was performed to investigate the use of odorant measurements for prediction of odor concentration in facilities with growing-finishing pigs and to analyze the odorant composition in facilities with different floor and ventilation systems. Air was sampled in Nalophan bags, odor concentrations were measured by dilution-to-threshold olfactometry, and concentrations of odorants were measured by proton-transfer-reaction mass spectrometry (PTR-MS). Olfactometry and chemical analyses were synchronized to take place at identical time intervals after sampling. A principal component analysis revealed that different facilities for growing-finishing pigs can be distinguished based on the odorants. Pit ventilation comprising a small amount of the total ventilation air (10-20%) in facilities with both room and pit ventilation can be used to concentrate odorants, whereas the room ventilation contains lower concentrations of most odorants. A partial least squares regression model demonstrated that prediction of the odor concentration based on odorants measured by PTR-MS is feasible. Hydrogen sulfide, methanethiol, trimethylamine, and 4-methylphenol were identified as the compounds having the largest influence on the prediction of odor concentration, whereas carboxylic acids had no significant influence. In conclusion, chemical measurement of odorants by PTR-MS is an alternative for expressing the odor concentration in facilities with growing-finishing pigs that can be used to increase the understanding of odor from different types of facilities and improve the development of odor reduction technologies.
[Sulzer2012] "Proton transfer reaction mass spectrometry and the unambiguous real-time detection of 2,4,6 trinitrotoluene.",
, vol. 84, no. 9: Ionicon Analytik Gesellschaft m.b.H., Eduard-Bodem-Gasse 3, A-6020 Innsbruck, Austria., pp. 4161–4166, May, 2012.
Fears of terrorist attacks have led to the development of various technologies for the real-time detection of explosives, but all suffer from potential ambiguities in the assignment of threat agents. Using proton transfer reaction mass spectrometry (PTR-MS), an unusual bias dependence in the detection sensitivity of 2,4,6 trinitrotoluene (TNT) on the reduced electric field (E/N) has been observed. For protonated TNT, rather than decreasing signal intensity with increasing E/N, which is the more usual sensitivity pattern observed in PTR-MS studies, an anomalous behavior is first observed, whereby the signal intensity initially rises with increasing E/N. We relate this to unexpected ion-molecule chemistry based upon comparisons of measurements taken with related nitroaromatic compounds (1,3,5 trinitrobenzene, 1,3 dinitrobenzene, and 2,4 dinitrotoluene) and electronic structure calculations. This dependence provides an easily measurable signature that can be used to provide a rapid highly selective analytical procedure to minimize false positives for the detection of TNT. This has major implications for Homeland Security and, in addition, has the potential of making instrumentation cost-effective for use in security areas. This study shows that an understanding of fundamental ion-molecule chemistry occurring in low-pressure drift tubes is needed to exploit selectivity and sensitivity for analytical purposes.
[Ruiz-Samblas2012] "Proton transfer reaction-mass spectrometry volatile organic compound fingerprinting for monovarietal extra virgin olive oil identification",
, vol. -: Elsevier, pp. -, 2012.
Proton transfer reaction-mass spectrometry (PTR-MS) is a relatively new technique that allows the fast and accurate qualification of the volatile organic compound (VOC) fingerprint. This paper describes the analysis of thirty samples of extra virgin olive oil, of five different varieties of olive fruit (Arbequina, Cornicabra, Frantoio, Hojiblanca, and Picual) by PTR-MS. A multivariate pattern recognition method (partial least square-discriminant analysis, PLS-DA) was applied on the full spectra fingerprint of the PTR-MS measurements. The multivariate model was doubly validated: firstly by means of internal validation (cross-validation) and secondly with an external validation data set. The results showed that the five varieties could be successfully distinguished within them. The proposed method provides a new valuable tool for extra virgin olive oil classification according to variety, and it could serve as a screening technique for the authentication of monovarietal extra-virgin olive oil and as a methodology to confirm that a variety is in agreement with claimed identity.
[Hartungen2012] "Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) with Real-Time Nosespace Air Sampling-an Essential Tool for Food and Flavor Analysis",
[Soukoulis2012] "PTR-TOF-MS Analysis for Influence of Milk Base Supplementation on Texture and Headspace Concentration of Endogenous Volatile Compounds in Yogurt",
Food and Bioprocess Technology
, vol. 5, no. 6: Springer, pp. 2085–2097, 2012.
In the present study, the effects of milk fat (0.3% and 3.5% w/w), solids non-fat (8.4% and 13% w/w), and modified tapioca starch (0%, 0.5%, 1.0%, 1.5%, and 2.0% w/w) concentrations on the textural and physicochemical properties as well as the concentration of several endogenous flavor compounds in the headspace of set and stirred yogurts were investigated. The novel proton transfer reaction time-of-flight mass spectrometry technique was implemented for the non-invasive determination of the amounts of volatile organic compounds in the samples headspace. Milk fat and skim milk powder supplementation of the milk samples increased significantly the firmness and adhesiveness of yogurts (p < 0.001) and improved the stability of the formed gels by increasing their water holding capacity and reducing the amounts of expulsed whey (3.94 and 5.1 g for the milk fat and SNF-fortified samples). Acetaldehyde was significantly (p < 0.001) higher in the low fat-unfortified systems (6.15 ± 0.48 and 5.6 ± 0.60 ppmv, respectively). A similar trend was also reported in the case of 2-propanone (0.91 ± 0.11 and 1.13 ± 0.07 ppmv), diacetyl (334 ± 37 and 350 ± 34 ppbv), 2,3-pentanedione (54 ± 6 and 55 ± 6 ppbv), and 2-butanone (56 ± 7 and 68 ± 5 ppbv) for the same systems. In contrast, the concentration of flavor compounds in the headspace with hydroxyl groups (ethanol and acetoin) increased (p < 0.001) by solid non-fat fortification of milk base (350 ± 32 and 206 ± 7 ppbv, respectively, for the systems fortified with skim milk powder). Modified tapioca starch addition improved the textural properties and gel stability of yogurts whereas affected only the ethanol concentration (222 ± 16 and 322 ± 55 for the control and 2.0% w/w containing systems, respectively). Our data suggested that the reinforcement of textural and structural properties combined with the protein binding affinity of the flavor compounds seemed to be responsible for the aforementioned observations. In the case of stirred yogurts, the gel breakdown did not provoke significant changes in the headspace concentration of the most compounds, with the exception of ethanol, acetoin, and 2,3-pentanedione being significantly (p < 0.05) higher in the stirred yogurts (267 ± 29, 153 ± 11, and 38 ± 1 ppbv, respectively) than set style ones (232 ± 19, 134 ± 9, and 45 ± 3 ppbv, respectively).
[Cappellin2012] "PTR-ToF-MS and data mining methods: a new tool for fruit metabolomics",
, vol. 8, no. 5: Springer, pp. 761–770, 2012.
Proton Transfer Reaction-Mass Spectrometry (PTR-MS) in its recently developed implementation based on a time-of-flight mass spectrometer (PTR-ToF-MS) has been evaluated as a possible tool for rapid non-destructive investigation of the volatile compounds present in the metabolome of apple cultivars and clones. Clone characterization is a cutting-edge problem in technical management and royalty application, not only for apple, aiming at unveiling real properties which differentiate the mutated individuals. We show that PTR-ToF-MS coupled with multivariate and data mining methods may successfully be employed to obtain accurate varietal and clonal apple fingerprint. In particular, we studied the VOC emission profile of five different clones belonging to three well known apple cultivars, such as ‘Fuji’, ‘Golden Delicious’ and ‘Gala’. In all three cases it was possible to set classification models which can distinguish all cultivars and some of the clones considered in this study. Furthermore, in the case of ‘Gala’ we also identified estragole and hexyl 2-methyl butanoate contributing to such clone characterization. Beside its applied relevance, no data on the volatile profiling of apple clones are available so far, our study indicates the general viability of a metabolomic approach for volatile compounds in fruit based on rapid PTR-ToF-MS fingerprinting.
[Heenan2012] "PTR-TOF-MS monitoring of in vitro and in vivo flavour release in cereal bars with varying sugar composition",
, vol. 131, no. 2: Elsevier, pp. 477–484, 2012.
In the present study, PTR-TOF-MS was applied to better understand the influence of sugar composition on flavour release in a strawberry flavoured cereal bar system. To achieve this, measurements were made both statically from the headspace above cereal bar samples (in vitro) and dynamically from flavour release in the nose space during consumption (in vivo). An artificial strawberry flavour of known constituents (17 flavour active volatile compounds) was used in the preparation of cereal bars. For in vitro measurements, eight samples varying in the glucose syrup solids 42DE to polydextrose ratio were assessed. Measurements clearly showed that the level of glucose syrup solids substitution by polydextrose influenced the release of the added flavour compounds. In addition, distinguishable differences were detected for the release of volatile compounds between samples with different levels of glucose syrup solids and polydextrose during in vivo measurements. The improved mass resolution, sensitivity and speed of PTR-TOF-MS enabled direct comparisons between the rate compounds reached the nose space, maximum nose space concentration of compounds, and the time after which compounds were no longer detected in the nose-space.
[Brilli2012] "Qualitative and quantitative characterization of volatile organic compound emissions from cut grass.",
Environ Sci Technol
, vol. 46, no. 7: Ionicon Analytik GmbH, Eduard-Bodem-Gasse 3, 6020 Innsbruck, Austria., pp. 3859–3865, Apr, 2012.
Mechanical wounding of plants triggers the release of a blend of reactive biogenic volatile organic compounds (BVOCs). During and after mowing and harvesting of managed grasslands, significant BVOC emissions have the potential to alter the physical and chemical properties of the atmosphere and lead to ozone and aerosol formation with consequences for regional air quality. We show that the amount and composition of BVOCs emitted per unit dry weight of plant material is comparable between laboratory enclosure measurements of artificially severed grassland plant species and in situ ecosystem-scale flux measurements above a temperate mountain grassland during and after periodic mowing and harvesting. The investigated grassland ecosystem emitted annually up to 130 mg carbon m(-2) in response to cutting and drying, the largest part being consistently represented by methanol and a blend of green leaf volatiles (GLV). In addition, we report the plant species-specific emission of furfural, terpenoid-like compounds (e.g., camphor), and sesquiterpenes from cut plant material, which may be used as tracers for the presence of given plant species in the ecosystem.
[Cappellin2012a] "On quantitative determination of volatile organic compound concentrations using proton transfer reaction time-of-flight mass spectrometry.",
Environ Sci Technol
, vol. 46, no. 4: IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Area, Via E. Mach, 1, 38010, S. Michele a/A, Italy., pp. 2283–2290, Feb, 2012.
Proton transfer reaction - mass spectrometry (PTR-MS) has become a reference technique in environmental science allowing for VOC monitoring with low detection limits. The recent introduction of time-of-flight mass analyzer (PTR-ToF-MS) opens new horizons in terms of mass resolution, acquisition time, and mass range. A standard procedure to perform quantitative VOC measurements with PTR-ToF-MS is to calibrate the instrument using a standard gas. However, given the number of compounds that can be simultaneously monitored by PTR-ToF-MS, such a procedure could become impractical, especially when standards are not readily available. In the present work we show that, under particular conditions, VOC concentration determinations based only on theoretical predictions yield good accuracy. We investigate a range of humidity and operating conditions and show that theoretical VOC concentration estimations are accurate when the effect of water cluster ions is negligible. We also show that PTR-ToF-MS can successfully be used to estimate reaction rate coefficients between H(3)O(+) and VOC at PTR-MS working conditions and find good agreement with the corresponding nonthermal theoretical predictions. We provide a tabulation of theoretical rate coefficients for a number of relevant volatile organic compounds at various energetic conditions and test the approach in a laboratory study investigating the oxidation of alpha-pinene.
[Juerschik2012] "Rapid and facile detection of four date rape drugs in different beverages utilizing proton transfer reaction mass spectrometry (PTR-MS).",
J Mass Spectrom
, vol. 47, no. 9: IONICON Analytik GmbH., Eduard-Bodem-Gasse 3, 6020, Innsbruck, Austria., pp. 1092–1097, Sep, 2012.
In this work, we illustrate the application of proton transfer reaction mass spectrometry (PTR-MS) in the field of food and drink safety. We present proof-of-principle measurements of four different drinks (water, tea, red wine and white wine) each spiked separately with four different date rape drugs (chloral hydrate, tricholorethanol, γ-butyrolactone and butanediol). At first, the ideal PTR-MS operating conditions (reduced electric field strength and monitoring the most abundant [fragment] ion) for detection of the drugs were determined utilizing a time-of-flight-based PTR-MS instrument. We then dissolved small quantities of the drugs (below the activation threshold for effects on humans) into the various types of drinks and detected them using a quadrupole-based PTR-MS instrument via two different sampling methods: (1) dynamic headspace sampling and (2) direct liquid injection. Both methods have their advantages and drawbacks. Only with dynamic headspace sampling can rape drug contaminations be detected within a timeframe of seconds, and therefore, this method is the most promising use of PTR-MS as a fast, sensitive and selective monitor for the detection of food and drink contamination.
[Farneti2012] "Rapid tomato volatile profiling by using proton-transfer reaction mass spectrometry (PTR-MS).",
J Food Sci
, vol. 77, no. 5: Horticultural Supply Chains Group, Wageningen Univ., Droevendaalsesteeg 1, 6708 PD Wageningen, The Netherlands. firstname.lastname@example.org, pp. C551–C559, May, 2012.
The availability of rapid and accurate methods to assess fruit flavor is of utmost importance to support quality control especially in the breeding phase. Breeders need more information and analytical tools to facilitate selection for complex multigenic traits such as flavor quality. In this study, it is shown that proton-transfer reaction mass spectrometry (PTR-MS) is a suitable method to monitor at high sensitivity the emission of volatiles determining the tomato aromatic profile such as hexanal, hexenals, methanol, ethanol, and acetaldehyde. The volatiles emitted by 14 tomato varieties (at red stage) were analyzed by 2 solvent-free headspace methods: solid-phase microextraction/gas chromatography MS and PTR-MS. Multivariate statistics (principal component analysis and cluster analysis) of the PTR-MS results allow an unambiguous separation between varieties, especially with a clear fingerprinting separation between the different tomato types: round truss, cocktail, and cherry tomatoes. PTR-MS was also successfully used to monitor the changes in volatile profiles during postharvest ripening and storage.
[Dam2012] "Real-time analysis of sulfur-containing volatiles in Brassica plants infested with root-feeding Delia radicum larvae using proton-transfer reaction mass spectrometry.",
, vol. 2012: Department of Ecogenomics , Institute for Water and Wetland Research (IWWR) , Radboud University Nijmegen , Nijmegen, 6525 AJ , The Netherlands., pp. pls021, 2012.
Plants damaged by herbivores emit a variety of volatile organic compounds (VOCs). Here we used proton-transfer reaction mass spectrometry (PTR-MS) as a sensitive detection method for online analysis of herbivore-induced VOCs. Previously, it was found that Brassica nigra plants emit several sulfur-containing VOCs when attacked by cabbage root fly (Delia radicum) larvae with m/z 60 as a marker for the formation of allylisothiocyanate from the glucosinolate sinigrin. We tested the hypothesis that m/z 60 emission occurs only in plants with sinigrin in their roots. Additionally, we tested the hypothesis that methanethiol, dimethylsulfide and dimethyldisulfide are only emitted after larval infestation.Proton-transfer reaction mass spectrometry was used to track sulfur-containing VOCs from six different species of Brassica over time. The roots were either artificially damaged or infested with cabbage root fly larvae. Glucosinolate profiles of the roots were analysed using high-pressure liquid chromatography and compared with VOC emissions.Brassica nigra, B. juncea and B. napus primarily emitted m/z 60 directly after artificial damage or root fly infestation. Sulfide and methanethiol emissions from B. nigra and B. juncea also increased after larval damage but much later (6-12 h after damage). Brassica rapa, B. oleracea and B. carinata principally emitted methanethiol after artificial and after larval damage. Brassica oleracea and B. carinata showed some increase in m/z 60 emission after larval damage. Comparison with root glucosinolate profiles revealed that sinigrin cannot be the only precursor for m/z 60.The principal compound emitted after root damage is determined by the plant species, and not by damage type or root glucosinolate composition. Once determined, the principal compounds may be used as markers for identifying damaged or infested plants. Further analyses of plant enzymes involved in the breakdown of sulfur compounds is needed to reveal the origin of sulfur-containing VOCs from plants.
[Mallette2012] "Resolution of volatile fuel compound profiles from Ascocoryne sarcoides: a comparison by proton transfer reaction-mass spectrometry and solid phase microextraction gas chromatography-mass spectrometry.",
, vol. 2, no. 1: Department of Chemical and Biological Engineering, Montana State University, Bozeman MT 59717, USA. BPeyton@coe.montana.edu., pp. 23, 2012.
Volatile hydrocarbon production by Ascocoryne sacroides was studied over its growth cycle. Gas-phase compounds were measured continuously with a proton transfer reaction-mass spectrometry (PTR-MS) and at distinct time points with gas chromatography-mass spectrometry (GC-MS) using head space solid phase microextraction (SPME). The PTR-MS ion signal permitted temporal resolution of the volatile production while the SPME results revealed distinct compound identities. The quantitative PTR-MS results showed the volatile production was dominated by ethanol and acetaldehyde, while the concentration of the remainder of volatiles consistently reached 2,000 ppbv. The measurement of alcohols from the fungal culture by the two techniques correlated well. Notable compounds of fuel interest included nonanal, 1-octen-3-ol, 1-butanol, 3-methyl- and benzaldehyde. Abiotic comparison of the two techniques demonstrated SPME fiber bias toward higher molecular weight compounds, making quantitative efforts with SPME impractical. Together, PTR-MS and SPME GC-MS were shown as valuable tools for characterizing volatile fuel compound production from microbiological sources.