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2013
[Schuhfried2013] Schuhfried, E., M. Probst, J. Limtrakul, S. Wannakao, E. Aprea, L. Cappellin, T. D. Märk, F. Gasperi, and F. Biasioli, "Sulfides: chemical ionization induced fragmentation studied with proton transfer reaction-mass spectrometry and density functional calculations.", J Mass Spectrom, vol. 48, no. 3: Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität Innsbruck, Technikerstr. 25, A-6020, Innsbruck, Austria., pp. 367–378, Mar, 2013.
Link: http://dx.doi.org/10.1002/jms.3153
Abstract
We report the energy-dependent fragmentation patterns upon protonation of eight sulfides (organosulfur compounds) in Proton Transfer Reaction-Mass Spectrometry (PTR-MS). Studies were carried out, both, experimentally with PTR-MS, and with theoretical quantum-chemical methods. Charge retention usually occurred at the sulfur-containing fragment for short chain sulfides. An exception to this is found in the unsaturated monosulfide allylmethyl sulfide (AMS), which preferentially fragmented to a carbo-cation at m/z 41, C3H5(+). Quantum chemical calculations (DFT with the M062X functional 6-31G(d,p) basis sets) for the fragmentation reaction pathways of AMS indicated that the most stable protonated AMS cation at m/z 89 is a protonated (cyclic) thiirane, and that the fragmentation reaction pathways of AMS in the drift tube are kinetically controlled. The protonated parent ion MH(+) is the predominant product in PTR-MS, except for diethyl disulfide at high collisional energies. The saturated monosulfides R-S-R' (with R<R') have little or no fragmentation, at the same time the most abundant fragment ion is the smaller R-S(+) fragment. The saturated disulfides R-S-S-R display more fragmentation than the saturated monosulfides, the most common fragments are disulfide containing fragments or long-chain carbo-cations. The results rationalize fragmentation data for saturated monosulfides and disulfides and represent a detailed analysis of the fragmentation of an unsaturated sulfide. Apart from the theoretical interest, the results are in support of the quantitative analysis of sulfides with PTR-MS, all the more so as PTR-MS is one of a few techniques that allow for ultra-low quantitative analysis of sulfides.
2012
[Aprea2012] Aprea, E., F. Morisco, F. Biasioli, P. Vitaglione, L. Cappellin, C. Soukoulis, V. Lembo, F. Gasperi, G. D'Argenio, V. Fogliano, et al., "Analysis of breath by proton transfer reaction time of flight mass spectrometry in rats with steatohepatitis induced by high-fat diet.", J Mass Spectrom, vol. 47, no. 9: IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Department, Via E. Mach, 1, 38010, S. Michele a/A, Italy. eugenio.aprea@iasma.it, pp. 1098–1103, Sep, 2012.
Link: http://dx.doi.org/10.1002/jms.3009
Abstract
Breath testing has been largely used as a diagnostic tool, but the difficulties in data interpretation and sample collection have limited its application. We developed a fast (< 20?s), on-line, non-invasive method for the collection and analysis of exhaled breath in awake rats based on proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) and applied it to investigate possible relationships between pathologies induced by dietary regime and breath composition. As a case study, we investigated rats with dietary induced non-alcoholic steatohepatitis (NASH) and modifications induced by coffee addition to the diet. We considered two different diets (standard and high fat) complemented with two different drinking possibilities (water or decaffeinated coffee) for a total of four groups with four rats each. Several spectrometric peaks were reliable markers for both dietary fat content and coffee supplementation. The high resolution and accuracy of PTR-ToF-MS allowed the identification of related compounds such as methanol, dimethyl sulphide, dimethyl sulphone and ammonia. In conclusion, the rapid and minimally invasive breath analysis of awake rats permitted the identification of markers related to diet and specific pathologic conditions and provided a useful tool for broader metabolic investigations.
[Schuhfried2012] Schuhfried, E., E. Aprea, L. Cappellin, C. Soukoulis, R. Viola, T. D. Maerk, F. Gasperi, and F. Biasioli, "Desorption kinetics with PTR-MS: Isothermal differential desorption kinetics from a heterogeneous inlet surface at ambient pressure and a new concept for compound identification", International journal of mass spectrometry, vol. -: Elsevier, pp. -, 2012.
Link: http://www.sciencedirect.com/science/article/pii/S1387380612000292
Abstract
Proton transfer reaction-mass spectrometry (PTR-MS) is a soft ionization mass spectrometric technique for monitoring volatile organic compounds (VOCs) with a very low limit of detection (LOD) (parts per trillion by volume) and excellent time resolution (split seconds). This makes PTR-MS a particularly interesting instrument for investigating surface desorption kinetics of volatile organic compounds (VOCs) under realistic conditions, i.e., at ambient pressure from a heterogeneous surface. Here, we report on the investigation of heterogeneous inlet surface kinetics with PTR-MS and based thereon, develop concepts to assist compound identification in PTR-MS. First, we studied differential isothermal desorption kinetics using heterogeneous inlet surface data measured by Mikoviny et al. [7] with their newly developed high-temp-PTR-MS. The best fit to their data is obtained with bimodal pseudo-first order kinetics. In addition, we explored the normalization of the data and calculated data points of the desorption isotherms. We found evidence that the interesting part of the isotherm can be linearized in a double log plot. Then we investigated the idea to use memory effects of the inlet system to assist compound identification. At the moment, the main problem is the dependence of the kinetics on the initial equilibrium gas phase adsorption concentration, and thus, the surface coverage. As a solution, we suggest an empirical, quasi-concentration independent, yet compound specific parameter: the normalized desorption time tnd describing the decline of the signal to 1/e2 of the initial concentration, normalized to an initial concentration of 10,000 counts per second (cps). Furthermore, we investigated property–property and structure–property relationships of this new parameter. Further possible improvements are discussed as well.
[Tasin2012] Tasin, M., L. Cappellin, and F. Biasioli, "Fast direct injection mass-spectrometric characterization of stimuli for insect electrophysiology by proton transfer reaction-time of flight mass-spectrometry (PTR-ToF-MS).", Sensors (Basel), vol. 12, no. 4: IASMA Research and Innovation Centre, Fondazione Edmund Mach, San Michele all'Adige, Italy. marco.tasin@slu.se, pp. 4091–4104, 2012.
Link: http://dx.doi.org/10.3390/s120404091
Abstract
Electrophysiological techniques are used in insect neuroscience to measure the response of olfactory neurons to volatile odour stimuli. Widely used systems to deliver an olfactory stimulus to a test insect include airstream guided flow through glass cartridges loaded with a given volatile compound on a sorbent support. Precise measurement of the quantity of compound reaching the sensory organ of the test organism is an urgent task in insect electrophysiology. In this study we evaluated the performances of the recent realised proton transfer reaction-time of flight mass-spectrometry (PTR-ToF-MS) as a fast and selective gas sensor. In particular, we characterised the gas emission from cartridges loaded with a set of volatile compounds belonging to different chemical classes and commonly used in electrophysiological experiments. PTR-ToF-MS allowed a fast monitoring of all investigated compounds with sufficient sensitivity and time resolution. The detection and the quantification of air contaminants and solvent or synthetic standards impurities allowed a precise quantification of the stimulus exiting the cartridge. The outcome of this study was twofold: on one hand we showed that PTR-ToF-MS allows monitoring fast processes with high sensitivity by real time detection of a broad number of compounds; on the other hand we provided a tool to solve an important issue in insect electrophysiology.
[JLTing2012] Ting, V. J. L., C. Soukoulis, P. Silcock, L. Cappellin, A. Romano, E. Aprea, P. J. Bremer, T. D. Märk, F. Gasperi, and F. Biasioli, "In Vitro and In Vivo Flavor Release from Intact and Fresh-Cut Apple in Relation with Genetic, Textural, and Physicochemical Parameters", Journal of food science, vol. 77, no. 11: Wiley Online Library, pp. C1226–C1233, 2012.
Link: http://onlinelibrary.wiley.com/doi/10.1111/j.1750-3841.2012.02947.x/full
Abstract
Flavor release from 6 commercial apple cultivars (Fuji, Granny Smith, Golden Delicious, Jonagold, Morgen Dallago, and Red Delicious) under static conditions (intact or fresh-cut samples) and during consumption of fresh-cut samples (nosespace) was determined by proton transfer reaction mass spectrometry. Textural (firmness, fracturability, flesh elasticity, and rupture) and physicochemical (pH, acidity, and water content) properties of the apples were also measured. Static headspace analysis of intact fruits revealed Fuji and Granny Smith apples had the lowest concentration for all measured flavor compounds (esters, aldehydes, alcohols, and terpenes), whereas Red Delicious apples had the highest. Fresh-cut samples generally showed a significant increase in total volatile compounds with acetaldehyde being most abundant. However, compared to intact fruits, cut Golden and Red Delicious apples had a lower intensity for ester related peaks. Five parameters were extracted from the nosespace data of peaks related to esters (m/z 43, 61), acetaldehyde (m/z 45), and ethanol (m/z 47): 2 associated with mastication (duration of mastication–tcon; time required for first swallowing event–tswal), and 3 related with in-nose volatile compound concentration (area under the curve–AUC; maximum intensity–Imax; time for achieving Imax–tmax). Three different behaviors were identified in the nosespace data: a) firm samples with low AUC and tswal values (Granny Smith, Fuji), b) mealy samples with high AUC, Imax, tswal values, and low tcon (Morgen Dallago, Golden Delicious), and c) firm samples with high AUC and Imax values (Red Delicious). Strengths and limitations of the methodology are discussed.
[Ting2012] Ting, V. J. L., C. Soukoulis, P. Silcock, L. Cappellin, A. Romano, E. Aprea, P. J. Bremer, T. D. Maerk, F. Gasperi, and F. Biasioli, "In vitro and in vivo flavor release from intact and fresh-cut apple in relation with genetic, textural, and physicochemical parameters.", J Food Sci, vol. 77, no. 11: Research and Innovation Centre, Foundation Edmund Mach, via Mach 1, San Michele all' Adige, (TN), Italy., pp. C1226–C1233, Nov, 2012.
Link: http://dx.doi.org/10.1111/j.1750-3841.2012.02947.x
Abstract
Flavor release from 6 commercial apple cultivars (Fuji, Granny Smith, Golden Delicious, Jonagold, Morgen Dallago, and Red Delicious) under static conditions (intact or fresh-cut samples) and during consumption of fresh-cut samples (nosespace) was determined by proton transfer reaction mass spectrometry. Textural (firmness, fracturability, flesh elasticity, and rupture) and physicochemical (pH, acidity, and water content) properties of the apples were also measured. Static headspace analysis of intact fruits revealed Fuji and Granny Smith apples had the lowest concentration for all measured flavor compounds (esters, aldehydes, alcohols, and terpenes), whereas Red Delicious apples had the highest. Fresh-cut samples generally showed a significant increase in total volatile compounds with acetaldehyde being most abundant. However, compared to intact fruits, cut Golden and Red Delicious apples had a lower intensity for ester related peaks. Five parameters were extracted from the nosespace data of peaks related to esters (m/z 43, 61), acetaldehyde (m/z 45), and ethanol (m/z 47): 2 associated with mastication (duration of mastication-t(con); time required for first swallowing event-t(swal)), and 3 related with in-nose volatile compound concentration (area under the curve-AUC; maximum intensity-I(max); time for achieving I(max)-t(max)). Three different behaviors were identified in the nosespace data: a) firm samples with low AUC and t(swal) values (Granny Smith, Fuji), b) mealy samples with high AUC, I(max), t(swal) values, and low t(con) (Morgen Dallago, Golden Delicious), and c) firm samples with high AUC and I(max) values (Red Delicious). Strengths and limitations of the methodology are discussed. PRACTICAL APPLICATION: Volatile compounds play a fundamental role in the perceived quality of food. Using apple cultivars, this research showed that in vivo proton transfer reaction mass spectrometry (PTR-MS) could be used to determine the relationship between the release of volatile flavor compounds and the physicochemical parameters of a real food matrix. This finding suggests that in vivo PTR-MS coupled with traditional physicochemical measurements could be used to yield information on flavor release from a wide range of food matrices and help in the development of strategies to enhance food flavor and quality.
[Papurello2012] Papurello, D., C. Soukoulis, E. Schuhfried, L. Cappellin, F. Gasperi, S. Silvestri, M. Santarelli, and F. Biasioli, "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.", Bioresour Technol, 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.
Link: http://dx.doi.org/10.1016/j.biortech.2012.09.033
Abstract
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.
[Soukoulis2012] Soukoulis, C., F. Biasioli, E. Aprea, E. Schuhfried, L. Cappellin, T. D. Märk, and F. Gasperi, "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.
Link: http://link.springer.com/article/10.1007/s11947-010-0487-1
Abstract
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] Cappellin, L., C. Soukoulis, E. Aprea, P. Granitto, N. Dallabetta, F. Costa, R. Viola, T. D. Märk, F. Gasperi, and F. Biasioli, "PTR-ToF-MS and data mining methods: a new tool for fruit metabolomics", Metabolomics, vol. 8, no. 5: Springer, pp. 761–770, 2012.
Link: http://link.springer.com/article/10.1007/s11306-012-0405-9
Abstract
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] Heenan, S., C. Soukoulis, P. Silcock, A. Fabris, E. Aprea, L. Cappellin, T. D. Märk, F. Gasperi, and F. Biasioli, "PTR-TOF-MS monitoring of in vitro and in vivo flavour release in cereal bars with varying sugar composition", Food chemistry, vol. 131, no. 2: Elsevier, pp. 477–484, 2012.
Link: http://www.sciencedirect.com/science/article/pii/S0308814611012660
Abstract
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.
[Cappellin2012a] Cappellin, L., T. Karl, M. Probst, O. Ismailova, P. M. Winkler, C. Soukoulis, E. Aprea, T. D. Maerk, F. Gasperi, and F. Biasioli, "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.
Link: http://dx.doi.org/10.1021/es203985t
Abstract
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.
2011
[Cappellin2011a] Cappellin, L., F. Biasioli, P. M. Granitto, E. Schuhfried, C. Soukoulis, F. Costa, T. D. Maerk, and F. Gasperi, "On data analysis in PTR-TOF-MS: From raw spectra to data mining", Sensors and actuators B: Chemical, vol. 155, no. 1: Elsevier, pp. 183–190, 2011.
Link: http://www.sciencedirect.com/science/article/pii/S0925400510009135
Abstract
Recently the coupling of proton transfer reaction ionization with a time-of-flight mass analyser (PTR-TOF-MS) has been proposed to realise a volatile organic compound (VOC) detector that overcomes the limitations in terms of time and mass resolution of the previous instrument based on a quadrupole mass analysers (PTR-Quad-MS). This opens new horizons for research and allows for new applications in fields where the rapid and sensitive monitoring and quantification of volatile organic compounds (VOCs) is crucial as, for instance, environmental sciences, food sciences and medicine. In particular, if coupled with appropriate data mining methods, it can provide a fast MS-nose system with rich analytical information. The main, perhaps even the only, drawback of this new technique in comparison to its precursor is related to the increased size and complexity of the data sets obtained. It appears that this is the main limitation to its full use and widespread application. Here we present and discuss a complete computer-based strategy for the data analysis of PTR-TOF-MS data from basic mass spectra handling, to the application of up-to date data mining methods. As a case study we apply the whole procedure to the classification of apple cultivars and clones, which was based on the distinctive profiles of volatile organic compound emissions.
[Biasioli2011] Biasioli, F., C. Yeretzian, T. D. Märk, J. Dewulf, and H. Van Langenhove, "Direct-injection mass spectrometry adds the time dimension to (B) VOC analysis", TrAC Trends in Analytical Chemistry, vol. 30, no. 7: Elsevier, pp. 1003–1017, 2011.
Link: http://www.sciencedirect.com/science/article/pii/S0165993611001269
Abstract
In the past decade, we have witnessed rapid development of direct-injection mass spectrometric (DIMS) technologies that combine ever-improving mass and time resolution with high sensitivity and robustness. Here, we review some of the most significant DIMS technologies, which have been applied to rapid monitoring and quantification of volatile organic compounds (VOCs) and biogenic VOCS (BVOCs). They include MS-e-noses, atmospheric-pressure chemical ionization (APCI), proton-transfer-reaction mass spectrometry (PTR-MS), and selected ion-flow-tube mass spectrometry (SIFT-MS). DIMS-based MS-e-noses provide the possibility to screen large sample sets and may yield rich analytical information. APCI is a widespread ionization method and pioneered DIMS in environmental and flavor-release applications. SIFT-MS and PTR-MS allow better control of precursor-ion generation and hence of the ionization process. SIFT-MS puts the focus on control of the ionization process, while PTR-MS does so on sensitivity. Most (B)VOCs of interest can be efficiently detected and often identified by DIMS, thanks also to the possibility of switching between different precursor ions and the recent realization of time-of-flight-based equipments. Finally, we give selected examples of applications for each of the key technologies, including research in food-quality control (MS-e-nose), flavor release (APCI), environmental sciences (PTR-MS) and health sciences (SIFT-MS).
[Cappellin2011] Cappellin, L., F. Biasioli, E. Schuhfried, C. Soukoulis, T. D. Maerk, and F. Gasperi, "Extending the dynamic range of proton transfer reaction time-of-flight mass spectrometers by a novel dead time correction.", Rapid Commun Mass Spectrom, vol. 25, no. 1: IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Area, Via E. Mach 1, 38010 S. Michele a/A, Italy., pp. 179–183, Jan, 2011.
Link: http://onlinelibrary.wiley.com/doi/10.1002/rcm.4819/abstract
Abstract
Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) allows for very fast simultaneous monitoring of volatile organic compounds (VOCs) in complex environments. In several applications, food science and food technology in particular, peaks with very different intensities are present in a single spectrum. For VOCs, the concentrations range from the sub-ppt all the way up to the ppm level. Thus, a large dynamic range is necessary. In particular, high intensity peaks are a problem because for them the linear dependency of the detector signal on VOC concentration is distorted. In this paper we present, test with real data, and discuss a novel method which extends the linearity of PTR-TOF-MS for high intensity peaks far beyond the limit allowed by the usual analytical correction methods such as the so-called Poisson correction. Usually, raw data can be used directly without corrections with an intensity of up to about 0.1 ions/pulse, and the Poisson correction allows the use of peaks with intensities of a few ions/pulse. Our method further extends the linear range by at least one order of magnitude. Although this work originated from the necessity to extend the dynamic range of PTR-TOF-MS instruments in agro-industrial applications, it is by no means limited to this area, and can be implemented wherever dead time corrections are an issue.
[Soukoulis2011] Soukoulis, C., F. Biasioli, E. Aprea, L. Cappellin, and F. Gasperi, "Proton transfer reaction time-of-flight mass spectrometry to determine changes in flavor compounds during Lagrein red wine maturation in wooden and stainless steel vessels", XIII Weurman flavour research symposium, 27-30 September 2011, Zaragoza, Spain, 2011.
Link: http://www.ionicon.com/sites/default/files/uploads/doc/contributions_ptr_ms_Conference_6.pdf
[Schuhfried2011] Schuhfried, E., F. Biasioli, E. Aprea, L. Cappellin, C. Soukoulis, A. Ferrigno, T. D. Maerk, and F. Gasperi, "PTR-MS measurements and analysis of models for the calculation of Henry's law constants of monosulfides and disulfides.", Chemosphere, vol. 83, no. 3: Institut fuer Ionenphysik und Angewandte Physik, Leopold Franzens Universitaet Innsbruck, Technikerstr. 25, A-6020 Innsbruck, Austria., pp. 311–317, Apr, 2011.
Link: http://dx.doi.org/10.1016/j.chemosphere.2010.12.051
Abstract
Sulfides are known for their strong odor impact even at very low concentrations. Here, we report Henry's law constants (HLCs) measured at the nanomolar concentration range in water for monosulfides (dimethylsulfide, ethylmethylsulfide, diethylsulfide, allylmethylsulfide) and disulfides (dimethyldisulfide, diethylsulfide, dipropylsulfide) using a dynamic stripping technique coupled to Proton Transfer Reaction-Mass Spectrometry (PTR-MS). The experimental data were compared with literature values and to vapor/solubility calculations and their consistency was confirmed employing the extra-thermodynamic enthalpy-entropy compensation effect. Our experimental data are compatible with reported literature values, and they are typically lower than averaged experimental literature values by about 10%. Critical comparison with other freely available models (modeled vapor/solubility; group and bond additivity methods; Linear Solvation Energy Relationship; SPARC) was performed to validate their applicability to monosulfides and disulfides. Evaluation of theoretical models reveals a large deviation from our measured values by up to four times (in units of Matm(-1)). Two group contribution models were adjusted in view of the new data, and HLCs for a list of sulfur compounds were calculated. Based on our findings we recommend the evaluation and adaption of theoretical models for monosulfides and disulfides to lower values of solubility and higher values of fugacity.
[Biasioli2011a] Biasioli, F., F. Gasperi, C. Yeretzian, and T. D. Maerk, "PTR-MS monitoring of VOCs and BVOCs in food science and technology", TrAC Trends in Analytical Chemistry, vol. 30, no. 7: Elsevier, pp. 968–977, 2011.
Link: http://www.sciencedirect.com/science/article/pii/S0165993611001233
Abstract
Volatile organic compounds (VOCs) and biogenic VOCs (BVOCs), in particular, are a major topic in food science and technology. They play an important role in the perception of odor and flavor and, thus, in food appreciation. Their fast, non-invasive detection helps to control product quality and to monitor fundamental and industrial processes. Furthermore, there is increasing concern about the impact of VOCs and BVOCs from food production on our environment and health. In this contribution, we discuss food-related applications of proton transfer reaction mass spectrometry (PTR-MS), an emerging technique that allows direct, fast, sensitive monitoring of VOCs. After introducing the principles of PTR-MS, we review its applications in food science and technology, highlighting its capabilities from using complete mass spectra as characteristic fingerprints all the way to identifying and quantifying single compounds in a complex food matrix. We end with a description of fundamental studies from food sciences and outline new opportunities offered by recent technological advances.
[DelPulgar2011] Del Pulgar}, Jé. Sánchez {, C. Soukoulis, F. Biasioli, L. Cappellin, C. García, F. Gasperi, P. Granitto, T. D. Maerk, E. Piasentier, and E. Schuhfried, "Rapid characterization of dry cured ham produced following different PDOs by proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS).", Talanta, vol. 85, no. 1: Food Technology, Facultad de Veterinaria, UEx, Campus Universitario s/n, 10003 Cáceres, Spain., pp. 386–393, Jul, 2011.
Link: http://dx.doi.org/10.1016/j.talanta.2011.03.077
Abstract
In the present study, the recently developed proton transfer reaction time of flight mass spectrometry (PTR-ToF-MS) technique was used for the rapid characterization of dry cured hams produced according to 4 of the most important Protected Designations of Origin (PDOs): an Iberian one (Dehesa de Extremadura) and three Italian ones (Prosciutto di San Daniele, Prosciutto di Parma and Prosciutto Toscano). In total, the headspace composition and respective concentration for nine Spanish and 37 Italian dry cured ham samples were analyzed by direct injection without any pre-treatment or pre-concentration. Firstly, we show that the rapid PTR-ToF-MS fingerprinting in conjunction with chemometrics (Principal Components Analysis) indicates a good separation of the dry cured ham samples according to their production process and that it is possible to set up, using data mining methods, classification models with a high success rate in cross validation. Secondly, we exploited the higher mass resolution of the new PTR-ToF-MS, as compared with standard quadrupole based versions, for the identification of the exact sum formula of the mass spectrometric peaks providing analytical information on the observed differences. The work indicates that PTR-ToF-MS can be used as a rapid method for the identification of differences among dry cured hams produced following the indications of different PDOs and that it provides information on some of the major volatile compounds and their link with the implemented manufacturing practices such as rearing system, salting and curing process, manufacturing practices that seem to strongly affect the final volatile organic profile and thus the perceived quality of dry cured ham.
[Galle2011] Galle, S. A., A. Koot, C. Soukoulis, L. Cappellin, F. Biasioli, M. Alewijn, and S. M. { van Ruth}, "Typicality and geographical origin markers of protected origin cheese from The Netherlands revealed by PTR-MS.", J Agric Food Chem, vol. 59, no. 6: RIKILT-Institute of Food Safety, Wageningen University and Research Centre , P.O. Box 230, 6700 EV Wageningen, The Netherlands., pp. 2554–2563, Mar, 2011.
Link: http://dx.doi.org/10.1021/jf104170r
Abstract
Volatile fingerprints of 30 cumin cheese samples of artisanal farmers' cheese of Leiden with EU Protected Designation of Origin (PDO) and 29 cumin cheese samples of varying commercial Dutch brands without PDO protection were used to develop authentication models. The headspace concentrations of the volatiles, as measured with high sensitivity proton-transfer mass spectrometry, were subsequently subjected to partial least-squares discriminant analysis (PLS-DA). Farmers' cheese of Leiden showed a distinct volatile profile with 27 and 9 out of the 60 predominant ions showing respectively significantly higher and lower concentrations in the headspace of the cheese in comparison to the other cumin cheeses. The PLS-DA prediction models developed classified in cross-validation 96% of the samples of PDO protected, artisanal farmers' cheese of Leiden correctly, against 100% of commercial cumin cheese samples. The characteristic volatile compounds were tentatively identified by PTR-time-of-flight-MS. A consumer test indicated differences in appreciation, overall flavor intensity, creaminess, and firmness between the two cheese groups. The consumers' appreciation of the cumin cheese tested was not influenced by the presence of a name label or PDO trademark.
2010
[Cappellin2010a] Cappellin, L., F. Biasioli, A. Fabris, E. Schuhfried, C. Soukoulis, T. D. Maerk, and F. Gasperi, "Improved mass accuracy in PTR-TOF-MS: Another step towards better compound identification in PTR-MS", International journal of mass spectrometry, vol. 290, no. 1: Elsevier, pp. 60–63, 2010.
Link: http://www.sciencedirect.com/science/article/pii/S1387380609003571
Abstract
Proton transfer reaction mass spectrometry (PTR-MS) provides on-line monitoring of volatile organic compounds (VOCs) with a low detection threshold and a fast response time. Commercially available set-ups are usually based on quadrupole analysers that, due to the unit mass resolution, do not provide useful analytical information besides the nominal mass of the ions detected. Recently new instruments based on time-of-flight (PTR-TOF-MS) analysers have been proposed and commercialized. They provide higher mass resolution and thus improve the analytical information contained in the spectra. Mass accuracy, however, is an issue that has not been considered in great detail in the published papers on PTR-TOF-MS so far. We show here that the mass accuracy obtained by a commercial apparatus can be improved by proper data analysis. In particular, internal calibration based on an improved algorithm allows for a mass accuracy that suffices for elemental determination in the most common situations. Achieving good mass accuracy is a fundamental step for further exploiting the analytical potential of PTR-MS.
[Cappellin2010] Cappellin, L., M. Probst, J. Limtrakul, F. Biasioli, E. Schuhfried, C. Soukoulis, T. D. Maerk, and F. Gasperi, "Proton transfer reaction rate coefficients between H< sub> 3 O< sup>+ and some sulphur compounds", International journal of mass spectrometry, vol. 295, no. 1: Elsevier, pp. 43–48, 2010.
Link: http://www.sciencedirect.com/science/article/pii/S138738061000206X
Abstract
Volatile sulphur compounds (VSCs) are key compounds in many fields of basic and applied science and technology, such as environmental sciences, food science, geochemistry, petrochemistry, agriculture, biology and medicine. Proton transfer reaction mass spectrometry (PTR-MS) allows for on-line monitoring of volatile organic compounds (VOCs) and, in particular, of VSCs with ultra low detection limits and a fast response time. In principle, with PTR-MS, absolute quantification of VOC concentrations without calibration is possible, provided the branching ratios are known. However, for this, the reaction rate coefficients between VOCs and the hydronium ion have also to be known. Several well-established theories may be used to determine ion-neutral molecule reaction rate coefficients. In the case of H3O+–VOC reactions proceeding in a PTR-MS drift tube, a key factor to be considered is the centre-of-mass energy, which is generally much higher than the thermal energy, due to the additional translational (drift) energy of the ion. Nevertheless, it is common practice to employ collision theories that do not show an explicit dependence on the centre-of-mass energy. First we review basic aspects of ion-neutral reactions in the PTR-MS drift tube and various methods to calculate reaction rate coefficients. Next, we calculate, on the basis of quantum chemical methods and different theoretical approaches for ion-molecule collisions, reaction rate coefficients between selected sulphur compounds and H3O+. Finally, we discuss proper methods for the calculations of ion-neutral molecule reaction rate coefficients in the context of PTR-MS and the corresponding experimental parameters involved.
[Soukoulis2010] Soukoulis, C., E. Aprea, F. Biasioli, L. Cappellin, E. Schuhfried, T. D. Maerk, and F. Gasperi, "Proton transfer reaction time-of-flight mass spectrometry monitoring of the evolution of volatile compounds during lactic acid fermentation of milk.", Rapid Commun Mass Spectrom, vol. 24, no. 14: IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Area, Via E. Mach, 1, 38010, S.Michele a/A, (TN), Italy., pp. 2127–3134, Jul, 2010.
Link: http://dx.doi.org/10.1002/rcm.4617
Abstract
We apply, for first time, the recently developed proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) apparatus as a rapid method for the monitoring of lactic acid fermentation (LAF) of milk. PTR-TOF-MS has been proposed as a very fast, highly sensitive and versatile technique but there have been no reports of its application to dynamic biochemical processes with relevance to the food industry. LAF is a biochemical-physicochemical dynamic process particularly relevant for the dairy industry as it is an important step in the production of many dairy products. Further, LAF is important in the utilization of the by-products of the cheese industry, such as whey wastewaters. We show that PTR-TOF-MS is a powerful method for the monitoring of major volatile organic chemicals (VOCs) formed or depleted during LAF, including acetaldehyde, diacetyl, acetoin and 2-propanone, and it also provides information about the evolution of minor VOCs such as acetic acid, 2,3-pentanedione, ethanol, and off-flavor related VOCs such as dimethyl sulfide and furfural. This can be very important considering that the conventional measurement of pH decrease during LAF is often ineffective due to the reduced response of pH electrodes resulting from the formation of protein sediments. Solid-phase microextraction gas chromatography/mass spectrometry (SPME-GC/MS) data on the inoculated milk base and final fermented product are also presented to supporting peak identification. We demonstrate that PTR-TOF-MS can be used as a rapid, efficient and non-invasive method for the monitoring of LAF from headspace, supplying important data about the quality of the final product and that it may be used to monitor the efficacy of manufacturing practices.
[Fabris2010] Fabris, A., F. Biasioli, P. M. Granitto, E. Aprea, L. Cappellin, E. Schuhfried, C. Soukoulis, T. D. Maerk, F. Gasperi, and I. Endrizzi, "PTR-TOF-MS and data-mining methods for rapid characterisation of agro-industrial samples: influence of milk storage conditions on the volatile compounds profile of Trentingrana cheese.", J Mass Spectrom, vol. 45, no. 9: IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Area, Via E. Mach, 1, 38010, S. Michele a/A, Italy., pp. 1065–1074, Sep, 2010.
Link: http://onlinelibrary.wiley.com/doi/10.1002/jms.1797/abstract
Abstract
Proton transfer reaction-mass spectrometry (PTR-MS), a direct injection mass spectrometric technique based on an efficient implementation of chemical ionisation, allows for fast and high-sensitivity monitoring of volatile organic compounds (VOCs). The first implementations of PTR-MS, based on quadrupole mass analyzers (PTR-Quad-MS), provided only the nominal mass of the ions measured and thus little chemical information. To partially overcome these limitations and improve the analytical capability of this technique, the coupling of proton transfer reaction ionisation with a time-of-flight mass analyser has been recently realised and commercialised (PTR-TOF-MS). Here we discuss the very first application of this new instrument to agro-industrial problems and dairy science in particular. As a case study, we show here that the rapid PTR-TOF-MS fingerprinting coupled with data-mining methods can quickly verify whether the storage condition of the milk affects the final quality of cheese and we provide relevant examples of better compound identification in comparison with the previous PTR-MS implementations. In particular, 'Trentingrana' cheese produced by four different procedures for milk storage are compared both in the case of winter and summer production. It is indeed possible to set classification models with low prediction errors and to identify the chemical formula of the ion peaks used for classification, providing evidence of the role that this novel spectrometric technique can play for fundamental and applied agro-industrial themes.
2009
[Gasperi2009] Gasperi, F., E. Aprea, F. Biasioli, S. Carlin, I. Endrizzi, G. Pirretti, and S. Spilimbergo, "Effects of supercritical CO< sub> 2 and N< sub> 2 O pasteurisation on the quality of fresh apple juice", Food chemistry, vol. 115, no. 1: Elsevier, pp. 129–136, 2009.
Link: http://www.sciencedirect.com/science/article/pii/S0308814608014234
Abstract
Supercritical pasteurisation is receiving increasing attention as an alternative technology for foodstuff pasteurisation, but often the possible effects on the perceptible quality are not sufficiently considered. To address this latter issue, besides standard microbial analysis, we here investigate the impact of CO2/N2O supercritical pasteurisation (100 bar, 36 °C and 10 min treatment time) on the quality traits of fresh apple juice, linked to consumer perception. Discriminative sensory analysis (triangle test) and basic chemical characterization (total solids, sugars, organic acids, polyphenols) could not clearly demonstrate any induced modification of the treated juice, while head space analysis of volatile compounds (both by GC–MS and PTR–MS) indicated a general depletion of the volatile compounds that must be considered in the development of a stabilization method based on supercritical gases.
[Aprea2009a] Aprea, E., F. Biasioli, S. Carlin, I. Endrizzi, and F. Gasperi, "Investigation of volatile compounds in two raspberry cultivars by two headspace techniques: solid-phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS) and proton-transfer reaction-mass spectrometry (PTR-MS).", J Agric Food Chem, vol. 57, no. 10: IASMA Research and Innovation Centre, Fondazione Edmund Mach, Food Quality and Nutrition Area, Via E Mach 1, S Michele all'Adige, TN 38010, Italy. eugenio.aprea@iasma.it, pp. 4011–4018, May, 2009.
Link: http://pubs.acs.org/doi/abs/10.1021/jf803998c
Abstract
The volatile compounds emitted by two raspberry varieties ( Rubus idaeus , cv. Polka and Tulameen) were analyzed, in both the case of fresh fruits and juices, by two headspace methods that are rapid, solvent-free, and with reduced or no sample pretreatment: solid-phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS) and proton-transfer reaction-mass spectrometry (PTR-MS). Multivariate analysis of the SPME/GC-MS results allows for an unambiguous sample discrimination for both mashed fruits and juices. PTR-MS instrumental fingerprint provides, in a faster way, similar qualitative information on the overall flavor profile. The two cultivars show both qualitative and quantitative differences. SPME/GC-MS analysis shows that alcohols and aldehydes are more abundant in the headspace of Tulameen as, e.g., hexanal and hexanol that induce herbaceous odor notes. This observation has been confirmed by sensory analysis. PTR-MS was also used to monitor rapid processes that modify the original aromatic profile, such as lipo-oxigenase activity induced by tissue damages occurring during industrial transformation, accidental mechanical damages, or as a consequence of chewing.

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Selected PTR-MS related Reviews

F. Biasioli, C. Yeretzian, F. Gasperi, T. D. Märk: PTR-MS monitoring of VOCs and BVOCs in food science and technology, Trends in Analytical Chemistry 30 (7) (2011).
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J. de Gouw, C. Warneke, T. Karl, G. Eerdekens, C. van der Veen, R. Fall: Measurement of Volatile Organic Compounds in the Earth's Atmosphere using Proton-Transfer-Reaction Mass Spectrometry. Mass Spectrometry Reviews, 26 (2007), 223-257.
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W. Lindinger, A. Hansel, A. Jordan: Proton-transfer-reaction mass spectrometry (PTR–MS): on-line monitoring of volatile organic compounds at pptv levels, Chem. Soc. Rev. 27 (1998), 347-375.
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Lists with PTR-MS relevant publications of the University of Innsbruck can be found here: Atmospheric and indoor air chemistry, IMR, Environmental Physics and Nano-Bio-Physics

 

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