Auswahl der wissenschaftlichen Literatur zum Thema „PTR-ToF-MS“

Abstract. Our understanding of formation processes, physical properties and climate/health effects of organic aerosols is still limited in part due to limited knowledge of organic aerosol composition. We present speciated measurements of organic aerosol composition by two methods: in-situ thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and offline two-dimensional gas chromatography with a time-of-flight mass spectrometer (GC×GC/TOF-MS). 153 compounds were identified using the GC×GC/TOF-MS, 123 of which were matched with 64 ions observed by the TD-PTR-MS. A reasonable overall correlation of 0.67 (r2) was found between the total matched TD-PTR-MS signal (sum of 64 ions) and the total matched GC×GC/TOF-MS signal (sum of 123 compounds). A reasonable quantitative agreement between the two methods was observed for most individual compounds with concentrations which were detected at levels above 2 ng m−3 using the GC×GC/TOF-MS. The analysis of monocarboxylic acids standards with TD-PTR-MS showed that alkanoic acids with molecular masses below 290 amu are detected well (recovery fractions above 60%). However, the concentrations of these acids were consistently higher on quartz filters (quantified offline by GC×GC/TOF-MS) than those suggested by in-situ TD-PTR-MS measurements, which is consistent with the semivolatile nature of the acids and corresponding positive filter sampling artifacts.

Abstract. Our understanding of formation processes, physical properties, and climate/health effects of organic aerosols is still limited in part due to limited knowledge of organic aerosol composition. We present speciated measurements of organic aerosol composition by two methods: in situ thermal-desorption proton-transfer-reaction mass spectrometry (TD-PTR-MS) and offline two-dimensional gas chromatography with a time-of-flight mass spectrometer (GC × GC/TOF-MS). Using the GC × GC/TOF-MS 153 compounds were identified, 123 of which were matched with 64 ions observed by the TD-PTR-MS. A reasonable overall correlation of 0.67 (r2) was found between the total matched TD-PTR-MS signal (sum of 64 ions) and the total matched GC × GC/TOF-MS signal (sum of 123 compounds) for the Los Angeles area. A reasonable quantitative agreement between the two methods was observed for most individual compounds with concentrations which were detected at levels above 2 ng m−3 using the GC × GC/TOF-MS. The analysis of monocarboxylic acids standards with TD-PTR-MS showed that alkanoic acids with molecular masses below 290 amu are detected well (recovery fractions above 60 %). However, the concentrations of these acids were consistently higher on quartz filters (quantified offline by GC × GC/TOF-MS) than those suggested by in situ TD-PTR-MS measurements, which is consistent with the semivolatile nature of the acids and corresponding positive filter sampling artifacts.

Abstract. During summer 2010, a proton transfer reaction – time of flight – mass spectrometer (PTR-TOF-MS) and a quadrupole proton transfer reaction mass spectrometer (PTR-MS) were deployed simultaneously for one month in an orange orchard in the Central Valley of California to collect continuous data suitable for eddy covariance (EC) flux calculations. The high time resolution (5 Hz) and high mass resolution (up to 5000 m/Δm) data from the PTR-TOF-MS provided the basis for calculating the concentration and flux for a wide range of volatile organic compounds (VOC). Throughout the campaign, 664 mass peaks were detected in mass-to-charge ratios between 10 and 1278. Here we present PTR-TOF-MS EC fluxes of the 27 ion species for which the vertical gradient was simultaneously measured by PTR-MS. These EC flux data were validated through spectral analysis (i.e., co-spectrum, normalized co-spectrum, and ogive). Based on inter-comparison of the two PTR instruments, no significant instrumental biases were found in either mixing ratios or fluxes, and the data showed agreement within 5% on average for methanol and acetone. For the measured biogenic volatile organic compounds (BVOC), the EC fluxes from PTR-TOF-MS were in agreement with the qualitatively inferred flux directions from vertical gradient measurements by PTR-MS. For the 27 selected ion species reported here, the PTR-TOF-MS measured total (24 h) mean net flux of 299 μg C m−2 h−1. The dominant BVOC emissions from this site were monoterpenes (m/z 81.070 + m/z 137.131 + m/z 95.086, 34%, 102 μg C m−2 h−1) and methanol (m/z 33.032, 18%, 72 μg C m−2 h−1). The next largest fluxes were detected at the following masses (attribution in parenthesis): m/z 59.048 (mostly acetone, 12.2%, 36.5 μg C m−2 h−1), m/z 61.027 (mostly acetic acid, 11.9%, 35.7 μg C m−2 h−1), m/z 93.069 (para-cymene + toluene, 4.1%, 12.2 μg C m−2 h−1), m/z 45.033 (acetaldehyde, 3.8%, 11.5 μg C m−2 h−1), m/z 71.048 (methylvinylketone + methacrolein, 2.4%, 7.1 μg C m−2 h−1), and m/z 69.071 (isoprene + 2-methyl-3-butene-2-ol, 1.8%, 5.3 μg C m−2 h−1). Low levels of emission and/or deposition (<1.6% for each, 5.8% in total flux) were observed for the additional reported masses. Overall, our results show that EC flux measurements using PTR-TOF-MS is a powerful new tool for characterizing the biosphere-atmosphere exchange including both emission and deposition for a large range of BVOC and their oxidation products.

Abstract. Volatile organic compound (VOC) mixing ratios measured by five independent instruments are compared at a forested site dominated by ponderosa pine (Pinus Ponderosa) during the BEACHON-ROCS field study in summer 2010. The instruments included a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), a Proton Transfer Reaction Quadrupole Mass Spectrometer (PTR-MS), a Fast Online Gas-Chromatograph coupled to a Mass Spectrometer (GC/MS; TOGA), a Thermal Dissociation Chemical Ionization Mass Spectrometer (PAN-CIMS) and a Fiber Laser-Induced Fluorescence Instrument (FILIF). The species discussed in this comparison include the most important biogenic VOCs and a selected suite of oxygenated VOCs that are thought to dominate the VOC reactivity at this particular site as well as typical anthropogenic VOCs that showed low mixing ratios at this site. Good agreement was observed for methanol, the sum of the oxygenated hemiterpene 2-methyl-3-buten-2-ol (MBO) and the hemiterpene isoprene, acetaldehyde, the sum of acetone and propanal, benzene and the sum of methyl ethyl ketone (MEK) and butanal. Measurements of the above VOCs conducted by different instruments agree within 20%. The ability to differentiate the presence of toluene and cymene by PTR-TOF-MS is tested based on a comparison with GC-MS measurements, suggesting a study-average relative contribution of 74% for toluene and 26% for cymene. Similarly, 2-hydroxy-2-methylpropanal (HMPR) is found to interfere with the sum of methyl vinyl ketone and methacrolein (MVK+MAC) using PTR-(TOF)-MS at this site. A study-average relative contribution of 85% for MVK+MAC and 15% for HMPR was determined. The sum of monoterpenes measured by PTR-MS and PTR-TOF-MS was generally 20–25% higher than the sum of speciated monoterpenes measured by TOGA, which included α-pinene, β-pinene, camphene, carene, myrcene, limonene, cineole as well as other terpenes. However, this difference is consistent throughout the study, and likely points to an offset in calibration, rather than a difference in the ability to measure the sum of terpenes. The contribution of isoprene relative to MBO inferred from PTR-MS and PTR-TOF-MS was smaller than 12% while GC-MS data suggested an average of 21% of isoprene relative to MBO. This comparison demonstrates that the current capability of VOC measurements to account for OH reactivity associated with the measured VOCs is within 20%.

Abstract. Volatile organic compound (VOC) mixing ratios measured by five independent instruments are compared at a forested site dominated by ponderosa pine (Pinus Ponderosa) during the BEACHON-ROCS field study in summer 2010. The instruments included a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), a Proton Transfer Reaction Quadrupole Mass Spectrometer (PTR-MS), a Fast Online Gas-Chromatograph coupled to a Mass Spectrometer (GC/MS; TOGA), a Thermal Dissociation Chemical Ionization Mass Spectrometer (PAN-CIMS) and a Fiber Laser-Induced Fluorescence Instrument (FILIF). The species discussed in this comparison include the most important biogenic VOCs and a selected suite of oxygenated VOCs that are thought to dominate the VOC reactivity at this particular site as well as typical anthropogenic VOCs that showed low mixing ratios at this site. Good agreement was observed for methanol, the sum of the oxygenated hemiterpene 2-methyl-3-buten-2-ol (MBO) and the hemiterpene isoprene, acetaldehyde, the sum of acetone and propanal, benzene and the sum of methyl ethyl ketone (MEK) and butanal. Measurements of the above VOCs conducted by different instruments agree within 20%. The ability to differentiate the presence of toluene and cymene by PTR-TOF-MS is tested based on a comparison with GC-MS measurements, suggesting a study-average relative contribution of 74% for toluene and 26% for cymene. Similarly, 2-hydroxy-2-methylpropanal (HMPR) is found to interfere with the sum of methyl vinyl ketone and methacrolein (MVK + MAC) using PTR-(TOF)-MS at this site. A study-average relative contribution of 85% for MVK + MAC and 15% for HMPR was determined. The sum of monoterpenes measured by PTR-MS and PTR-TOF-MS was generally 20–25% higher than the sum of speciated monoterpenes measured by TOGA, which included α-pinene, β-pinene, camphene, carene, myrcene, limonene, cineole as well as other terpenes. However, this difference is consistent throughout the study, and likely points to an offset in calibration, rather than a difference in the ability to measure the sum of terpenes. The contribution of isoprene relative to MBO inferred from PTR-MS and PTR-TOF-MS was smaller than 12% while GC-MS data suggested an average of 21% of isoprene relative to MBO. This comparison demonstrates that the current capability of VOC measurements to account for OH reactivity associated with the measured VOCs is within 20%.

Abstract. During summer 2010, a proton transfer reaction-time of flight-mass spectrometer (PTR-TOF-MS) and a standard proton transfer reaction mass spectrometer (PTR-MS) were deployed simultaneously for one month in an orange orchard in the Central Valley of California to collect continuous data suitable for eddy covariance (EC) flux calculations. The high time resolution (5 Hz) and high mass resolution (up to 5000 m Δ m−1) data from the PTR-TOF-MS provided the basis for calculating the concentration and flux for a wide range of volatile organic compounds (VOC). Throughout the campaign, 664 mass peaks were detected in mass-to-charge ratios between 10 and 1278. Here we present PTR-TOF-MS EC fluxes of the 27 ion species for which the vertical gradient was simultaneously measured by PTR-MS. These EC flux data were validated through spectral analysis (i.e. co-spectrum, normalized co-spectrum, and ogive). Based on inter-comparison of the two PTR instruments, no significant instrumental biases were found in either mixing ratios or fluxes, and the data showed agreement within 5% on average for methanol and acetone. For the measured biogenic volatile organic compounds (BVOC), the EC fluxes from PTR-TOF-MS were in agreement with the qualitatively inferred flux directions from vertical gradient measurements by PTR-MS. For the 27 selected ion species reported here, the PTR-TOF-MS measured total (24 h) mean net flux of 299 μg C m−2 h−1. The dominant BVOC emissions from this site were monoterpenes (m/z 81.070 + m/z 137.131 + m/z 95.086, 34%, 102 μg C m−2 h−1) and methanol (m/z 33.032, 18%, 72 μg C m−2 h−1). The next largest fluxes were detected at the following masses (attribution in parenthesis): m/z 59.048 (mostly acetone, 12.2%, 36.5 μg C m−2 h−1), m/z 61.027 (mostly acetic acid, 11.9%, 35.7 μg C m−2 h−1), m/z 93.069 (para-cymene + toluene, 4.1%, 12.2 μg C m−2 h−1), m/z 45.033 (acetaldehyde, 3.8%, 11.5 μg C m−2 h−1), m/z 71.048 (methylvinylketone + methacrolein, 2.4%, 7.1 μg C m−2 h−1), and m/z 69.071 (isoprene + 2-methyl-3-butene-2-ol, 1.8%, 5.3 μg C m−2 h−1). Low levels of emission and/or deposition (<1.6% for each, 5.8% in total flux) were observed for the additional reported masses. Overall, our results show that EC flux measurements using PTR-TOF-MS is a powerful new tool for characterizing the biosphere-atmosphere exchange including both emission and deposition for a large range of BVOC and their oxidation products.

Abstract. Volatile organic compounds (VOCs) play important roles in the tropospheric atmosphere. In this study, VOCs were measured at an urban site in Guangzhou, one of the megacities in the Pearl River Delta (PRD), using a gas chromatograph–mass spectrometer/flame ionization detection (GC–MS/FID) and a proton transfer reaction time-of-flight mass spectrometer (PTR-ToF-MS). Diurnal profile analyses show that stronger chemical removal by OH radicals for more reactive hydrocarbons occurs during the daytime, which is used to estimate the daytime average OH radical concentration. In comparison, diurnal profiles of oxygenated volatile organic compounds (OVOCs) indicate evidence of contributions from secondary formation. Detailed source analyses of OVOCs, using a photochemical age-based parameterization method, suggest important contributions from both primary emissions and secondary formation for measured OVOCs. During the campaign, around 1700 ions were detected in PTR-ToF-MS mass spectra, among which there were 462 ions with noticeable concentrations. VOC signals from these ions are quantified based on the sensitivities of available VOC species. OVOC-related ions dominated PTR-ToF-MS mass spectra, with an average contribution of 73 % ± 9 %. Combining measurements from PTR-ToF-MS and GC–MS/FID, OVOCs contribute 57 % ± 10 % to the total concentration of VOCs. Using concurrent measurements of OH reactivity, OVOCs measured by PTR-ToF-MS contribute greatly to the OH reactivity (19 % ± 10 %). In comparison, hydrocarbons account for 21 % ± 11 % of OH reactivity. Adding up the contributions from inorganic gases (48 % ± 15 %), ∼ 11 % (range of 0 %–19 %) of the OH reactivity remains `missing”, which is well within the combined uncertainties between the measured and calculated OH reactivity. Our results demonstrate the important roles of OVOCs in the emission and evolution budget of VOCs in the urban atmosphere.

Abstract. The recently developed PTR-TOF instrument was evaluated to measure methanol fluxes emitted from grass land using the eddy covariance method. The high time resolution of the PTR-TOF allowed storing full mass spectra up to m/z 315 with a frequency of 10 Hz. Three isobaric ions were found at a nominal mass of m/z 33 due to the high mass resolving power of the PTR-TOF. Only one of the three peaks contributed to eddy covariance fluxes. The exact mass of this peak agrees well with the exact mass of protonated methanol (m/z 33.0335). The eddy covariance methanol fluxes measured with PTR-TOF were compared to virtual disjunct eddy covariance methanol fluxes simultaneously measured with a conventional PTR-MS. The methanol fluxes from both instruments show excellent agreement.

Abstract. The recently developed PTR-TOF instrument was evaluated to measure methanol fluxes emitted from grass land using the eddy covariance method. The high time resolution of the PTR-TOF allowed storing full mass spectra up to m/z 315 with a frequency of 10 Hz. Three isobaric ions were found at a nominal mass of m/z 33 due to the high mass resolving power of the PTR-TOF. Only one of the three peaks contributed to eddy covariance fluxes. The exact mass of this peak agrees well with the exact mass of protonated methanol (m/z 33.0335). The eddy covariance methanol fluxes measured with PTR-TOF were compared to virtual disjunct eddy covariance methanol fluxes simultaneously measured with a conventional PTR-MS. The methanol fluxes from both instruments show excellent agreement.

Abstract. This paper reports the fluxes and mixing ratios of biogenically emitted volatile organic compounds (BVOCs) 4 m above a mixed oak and hornbeam forest in northern Italy. Fluxes of methanol, acetaldehyde, isoprene, methyl vinyl ketone + methacrolein, methyl ethyl ketone and monoterpenes were obtained using both a proton transfer reaction-mass spectrometer (PTR-MS) and a proton transfer reaction-time of flight-mass spectrometer (PTR-ToF-MS) together with the methods of virtual disjunct eddy covariance (PTR-MS) and eddy covariance (PTR-ToF-MS). Isoprene was the dominant emitted compound with a mean day-time flux of 1.9 mg m-2 h-1. Mixing ratios, recorded 4 m above the canopy, were dominated by methanol with a mean value of 6.2 ppbv over the 28 day measurement period. Comparison of isoprene fluxes calculated using the PTR-MS and PTR-ToF-MS showed very good agreement while comparison of the monoterpene fluxes suggested a slight over estimation of the flux by the PTR-MS. A basal isoprene emission rate for the forest of 1.7 mg m-2 h-1 was calculated using the MEGAN isoprene emissions algorithms (Guenther et al., 2006). A detailed tree species distribution map for the site enabled the leaf-level emissions of isoprene and monoterpenes recorded using GC-MS to be scaled up to produce a "bottom-up" canopy-scale flux. This was compared with the "top-down" canopy-scale flux obtained by measurements. For monoterpenes, the two estimates were closely correlated and this correlation improved when the plant species composition in the individual flux footprint was taken into account. However, the bottom-up approach significantly underestimated the isoprene flux, compared with the top-down measurements, suggesting that the leaf-level measurements were not representative of actual emission rates.

L'étude du comportement dynamique des substances actives pendant l'épandage de produits insecticides ménagers commerciaux dans les atmosphères intérieures nécessite le développement et l'adaptation de procédures analytiques de mesure en ligne ayant une résolution temporelle élevée. Un HS-PTR-MS et un HR-ToF-AMS ont par conséquent été utilisés pour mesurer les contaminants à la fois en phase gazeuse et particulaire. Les substances actives ciblées par cette étude appartiennent à la famille des pyréthrinoïdes, présentes dans différentes formulations commerciales du type diffuseurs électriques et sprays aérosols, qui ont été appliqués dans une pièce d'étude simulant une atmosphère réelle dans la maison expérimentale MARIA du Centre Scientifique et Technique du Bâtiment. Les résultats de ces mesures montrent des pics de concentration compris entre 1,5 et 8,5 µg.m-3, après 8 heures de branchement des diffuseurs électriques. Les pics de concentration des substances actives après l'application des sprays peuvent atteindre plusieurs dizaines de µg.m-3. La ventilation et la sédimentation des aérosols apparaissent comme des mécanismes majeurs d'élimination des polluants du compartiment air. Par ailleurs, une distribution importante des substances actives avec les surfaces de la pièce (murs, sol, plafond, particules en suspension et poussières) est observée. L'évaluation de l'exposition par inhalation aux produits insecticides étudiés montre qu'il n'existe a priori pas de risque pour la santé. Néanmoins, une évaluation intégrée, prenant en compte toutes les voies d'exposition est nécessaire avant de conclure à une absence de risque sanitaire
The study of the dynamic behaviour of the active substances during the application of commercial household insecticide products in indoor atmospheres requires the development of the adaptation of on-line analytical procedures with high time resolution. A HS-PTR-MS and a HR-ToF-AMS have therefore been used to measure contaminants both in the gaseous and particulate phase. The active substances targeted by this study belong to the pyrethroids, which are present in different commercial formulations like electric vaporizers and sprays that were applied in a full-scale test room simulating a real atmosphere in the experimental house MARIA of the French scientific and technical centre for building. The results of these measurements show that peak concentrations during a 8h-emission of electric vaporizers range from 1,5 et 8,5 µg.m-3. The peak concentrations of active substances during spraying can reach several dozens of µg.m-3. Ventilation and deposition of aerosols are major elimination mechanisms of pollutants from the air compartment. Moreover, an important distribution of active substances with the surfaces of the room (walls, floor, ceiling, suspended particles and dust) is observed. The evaluation of inhalation exposure to the studied insecticide products show that adverse effects are not likely to occur. Nevertheless, to conclude that these products are safe, it is necessary to perform an integrated evaluation, taking into account all exposure routes

Volatile organic compounds (VOCs) are ubiquitous in the Earth’s atmosphere. VOCs are produced from biogenic sources such as forests, or anthropogenic sources such as fossil fuel combustion. Many areas of research involve measuring VOCs, from atmospheric science, to medical science and homeland security with implications for health, the environment, and safety. It is crucial that VOCs are detected quickly and with a high sensitivity: proton transfer reaction - mass spectrometry (PTR-MS) offers a solution and potential enhancements of the PTR-MS technique are discussed here. A drift tube capable of simultaneously functioning as an ion funnel is demonstrated in PTR-MS for the first time enabling a much higher proportion of ions to exit the drift tube and enter the mass spectrometer than would otherwise be the case. An increase in the detection sensitivity for VOCs of up to two orders of magnitude and an increase in Limit of Detection of one order of magnitude is delivered, allowing lower concentrations of VOCs to be detected. An alternate way to change how the drift tube behaves is to alter the buffer gas. The collision energy within the drift tube is investigated in order to ascertain what advantages changing the buffer gas from nitrogen to argon yields with respect to sensitivity and fragmentation of analytes. For several compounds, the sensitivity is increased and fragmentation reduced. If sensitivity can be increased and/or fragmentation reduced within a complex mixture of analyte ions, then analysis of these mixtures will be simplified. Finally, a standard PTR-MS instrument is compared with the ion funnel equipped PTR-MS instrument in an urban, megacity (ClearfLo campaign, London, UK) in order to test the instrument and enhanced sensitivity for field measurements.

La miniaturisation et la complexification croissante des composants microélectroniques induit une sensibilisation et une fragilisation accrue des composants vis-à-vis des contaminations présentes dans les zones de productions appelées “salles blanches”. Dans ces espaces, le contrôle actuel de la contamination organique n’est pas suffisant puisqu’il ne permet pas d’éviter la contamination de surface des plaquettes de silicium et des optiques des robots de production utilisés pour la photolithographie. Un contrôle accru des concentrations des contaminants organiques dans les atmosphères des salles blanches devient donc nécessaire et de nouvelles méthodes analytiques doivent être développées et validées. Dans le cadre de ce travail, des méthodes d’analyse ont été développées et validées afin de disposer d’une gamme d’outils permettant un suivi rigoureux des contaminations. Ces outils permettent d’identifier et de quantifier les contaminations surfaciques des plaquettes de silicium par des composés organiques semi-volatils (phtalates et organophosphorés) mais aussi de déterminer les concentrations de composés organiques volatils présents dans l’atmosphère des salles blanches. Ces méthodes font appel aux technologies du WOS/ATD-GC-MS « Wafer Outgassing System/Automated Thermal Desorber–Gas Chromatography–Mass Spectrometry » et de la DART-ToF-MS « Direct Analysis in Real Time-Time of Flight–Mass Spectrometry » pour les analyses de surfaces et au PTR-ToF-MS « Proton Transfer Reaction – Time of Flight - Mass Spectrometry » pour l’analyse de l’atmosphère
The recent advances in the miniaturization and complexification of microelectronic components induce an increase in the sensitivity of these components regarding the organic contamination present in the production zone called “clean room”. Although, the control of organic contamination in the clean room is very rigorous it does not avoid the contamination of silicon wafer surfaces and robot lenses used in the photolithography process. The later implies that new analytical methodologies should be developed and validated. In this work, analytical methods were developed and validated in order to have a panel of tools which allows careful monitoring of organic contaminants. These tools allow the identification and quantitation of the contamination of silicon wafer surface by semi-volatiles organic compounds (phthalates and organophosphates) and the determination of volatile organic compounds concentrations in the clean room atmosphere. These methods uses the WOS/ATD-GC-MS « Wafer Outgassing System/Automated Thermal Desorber–Gas Chromatography–Mass Spectrometry » technology and the DART-ToF-MS « Direct Analysis in Real Time-Time of Flight–Mass Spectrometry » technology for wafer surface analysis and the PTR-ToF-MS « Proton Transfer Reaction – Time of Flight - Mass Spectrometry » technology for gas-phase analysis

The thesis is focused on electrical discharge in liquid solutions, in particular in ethanol solutions. In the theoretical section, the plasma is defined along with its important parameters, types of plasma generation and usage of plasma technologies. Main part is focused on the discharges in water solutions. Electric discharges in liquid solutions enable physical processes (shock waves, UV radiaton, electric current) as well as chemical ones (generation of radicals and ions). Both types of the processes are used in many fields – medicine (tool sterilization, destruction of pathogens), consumer technologies (surface adjustemen, processing of the textiles, surface clearing) of environmental protection (clearing water, decomposition of organic compounds). Goal of the thesis was to analyze discharge products on ethanol solution. Multiple samples were measured and concentration od selected products was monitored during the measurement – ethanol, acetone and acetaldehyde. PTR-TOF-MS method was used to collect and analyze the data. This method is well used thanks to quick response and immediate measurement. It produce the reset accurate enough for our purpose. It would be more efficient to use this method in combination with another analytical metohod in the future research, e.g. gas chromatography.

An intercomparison exercise of the world-harmonized light-duty vehicle test procedure (WLTP) aiming at measuring ethanol, formaldehyde and acetaldehyde emissions from a flex-fuel light-duty vehicle using E85 was conducted in the Vehicle Emission Laboratory (VELA) at the European Commission Joint Research Centre (EC-JRC), Ispra, Italy. The instruments used during the intercomparison allowed online measurements of these compounds directly from the diluted exhaust. Measurements were done either in real time or immediately after the test. The measurement and analysis of exhaust emissions over the world-harmonized light-duty vehicle test cycle was done by means of Fourier transform infrared spectroscopy (FTIR), proton transfer reaction-mass spectrometry (PTR-Qi-ToF-MS), photoacoustic spectroscopy (PAS) and gas chromatography (GC). Results showed that online systems can perform measurements from the vehicle diluted exhaust assuring a good repeatability (within instrument variance) and reproducibility (between instrument variance) of the results. Measurements from all the instruments were in good agreement (|Z-score| < 2). Results showed that online systems can perform measurements from the vehicle diluted exhaust assuring the reproducibility and repeatability of the results. Results obtained measuring at the tailpipe using a FTIR were in good agreement with those acquired measuring at the constant volume sampler (CVS). Considering the low sensitivity of the current technique used to measure hydrocarbons emissions towards oxygenated compounds (flame ionization detector; FID), non-methane organic gases (NMOG) were calculated applying their FID response factors to the measured emissions of ethanol, acetaldehyde and formaldehyde. NMOG resulted to be up to 74% higher than measured non-methane hydrocarbons (NMHC).

In recent years, consumers have become increasingly interested in the quality aspects of food. Food quality, in turn, is strongly related to the sensory characteristics such as the flavor. Several scientific studies have shown that the Volatile Organic Compounds (VOCs) released by the food are related to the flavor and can be considered as assistive markers in the production chain. Today, the analysis of VOCs requires fast, non-invasive, and solvent free devices. It has been shown that the VOCs can be extracted, identified, and measured with a Gas Chromatography-Mass Spectrometry (GC-MS) without any pre-concentration or pre-treatment of the food. The main objective of this PhD thesis was to investigate the presence of volatile compounds in dairy products. More precisely, this study aimed in i) qualifying and quantifying VOCs in dairy products, ii) examining their formation and iii) integrating knowledge on VOCs by tracking their release during the whole production process from the raw materials till the final dairy product. In addition, statistical analysis was applied to link VOCs with the genetic characterization of animals, dairy system and individual cow-factors (e.g. stage of lactation, order of parity and milk yield). The identification and quantification of VOCs were performed using fast and non-invasive analytical approaches (Solid Phase Micro Extraction/Gas Chromatography-Mass Spectrometry SPME/GC-MS and Proton Transfer Reaction-Time of Flight-Mass Spectrometry PTR-ToF-MS) that can monitor the evolution of VOCs. To achieve the overall goal, the research was partitioned in four interrelated subparts as described below. The aim of the first chapter was to study the VOCs presence in the headspace of cheese. To this purpose, 150 cheeses ripened for two months were used. The cheeses were obtained through an individual model cheese-making approach using milk from individual Brown Swiss cows. Animals reared in 30 herds belonging to different dairy systems, from traditional (typical of the mountainous area) to modern ones. The study identified 55 VOCs classified in the chemical families of free fatty acids, esters, alcohols, aldehydes, ketones, lactones, terpenes, and pyrazines. We found that dairy system and individual cow characteristics (lactation stage, order of parity and daily milk yield) influenced the volatile compounds. In order, to test the instrument reproducibility and the model cheese-making procedure; data of GC analysis, order of injection of the sample into instrument, and vat were included in the statistical model. In many cases, these analytical factors did not affect the amount of VOCs released by cheese. In the second chapter, the potential of a new spectrometric technique (PTR-ToF-MS) was investigated to study cheese quality traits on a large scale. The PTR-ToF-MS allows direct injection of the sample headspace without extraction or pre-concentration steps, has a shorter analysis time (only a few seconds per sample) and greater sensitivity that permit to monitor on-line the evolution of volatile compounds. The resulting spectral information can provide a very detailed description of samples, which is useful for characterizing food quality and typicality. In particular, we analyzed the volatile fingerprint of 1,075 model cheeses produced using individual milk of Brown Swiss cows reared in 72 herds of different dairy systems. The output of PTR (spectrum) was characterized by more than 600 spectrometric peaks (variables). After removing interfering ions and background noise a set of 240 peaks was selected. Further, based on the results of the first contribution and literature, 61 peaks were identified. These peaks represent the major part of the cheese flavor. To summarize the amount of information, a multivariate analysis (PCA) was applied associating principal components (PC) with the 240 spectrometric peaks. Following, we tried to characterize the PCs through the correlations between PCs and the spectrometric peaks. The effects of dairy system, herd within dairy system, individual cows characteristics (lactation stage, order of parity and milk yield), and vat used for the cheese-making on the PCs and on the 240 peaks were analyzed. Dairy system was correlated with PC and 57 spectrometric peaks, especially when the herds were using Total Mixer Ration (TMR) as feeding technique, including or not maize silage in the diets. Regarding the individual animal characteristics, the most significant effect was the stage of lactation (139 peaks), followed by milk yield and parity, with 31 and 21 peaks, respectively. Finally, the vat used for the cheese-making was not found to be significant, confirming the good reproducibility of the model cheese-making procedure used to study cheese quality aspects. In the third chapter, the effect of cows’ genetics to the VOCs of ripened cheeses was assessed. Principal components and the 240 spectrometric peaks (as described above in the second contribution) were used fitting an animal model in a Bayesian framework. On average, heritability (h2) of 7% for PCs was found, which is similar to h2 of somatic cell count and much lower than the h2 of milk fat content and daily milk yield. It is interesting to note that only a small proportion of peaks showed very low h2 (<7%). The major part of them showed values similar to those found for PCs, while forty peaks presented heritability similar to that of milk yield and other milk quality traits. The variability attributed to the herd was different for the various PC. Results suggest a potential of improvement for several cheese VOCs through genetic selection in dairy cow breeding programs. The aim of the fourth chapter was to study the effect of summer transhumance on the quality traits of dairy products. Due to the extended work, this contribution was further splitted into two parts. In the first part, the evolution of milk and cheese quality characteristics were studied, while in the second part the evolution of VOC content of dairy products was analyzed. For the first part, chemical characteristics and technological properties of 11 dairy products obtained during summer transhumance of cows to Alpine pastures (Malga) were analyzed. Dairy products obtained throughout this period are known to give origin to high-value, healthier products, and extra tasty,. Bulk milk from 148 dairy cows reared day and night on Alpine pasture (1,860 m a.s.l.) was used. We performed 7 experimental cheese-making according to traditional mountain techniques, one every two weeks, using milk produced during the summer transhumance (from June to September). For each cheese-making we collected: milk from the evening milking (day before the cheese-making), the same milk the following morning (after natural creaming), the cream separated, the whole milk from the morning milking, the milk in vat obtained mixing the creamed evening milk with the whole morning milk, the fresh curd, the whey, the ricotta obtained from whey, and the residual scotta. Moreover, the curd was used to produce typical “Malga” cheese that was ripened for 6 and 12 months. The chemical characteristics were measured with infrared technology. Results highlighted variation in milk yield, milk chemical composition, cheese yield and curd recoveries and/or loss of nutrients in the traditional cheese-making. In particular, a reduction of milk yield, fat, protein and lactose contents of milk during summer transhumance was observed. Nevertheless, the return to lowland farming systems of the cows at the end of grazing season, positively affected milk yield and milk chemical composition. The average of cheese yield was 14.2%, while recoveries of fat, protein, total solids and energy were 85.1%, 77.8%, 49.4% and 58.1%, respectively. These results were in accordance to those found in the literature. For the second part of this chapter, the VOCs content of sample headspace was measured through SPME/GC-MS. Forth nine VOCs belonging to the chemical families of alcohols, aldehydes, free fatty acids, ketones, esters, lactones, terpenes, phenolic, and sulphur compounds were detected. In addition, the evolution of VOCs and their chemical family across the cheese- and ricotta-making processing as well as during the cheese ripening period was tracked. The comparison between VOCs concentration of 4 types of milk (whole evening, creaming milk, whole morning, milk in vat) showed that the creaming process significantly affected about half of all the volatile organic compounds analyzed, followed by the effects of milking (evening milking vs. morning milking) and the mixing (creamed milk mixed with whole morning milk). In general, the cream, in contrast to curd and ricotta, showed higher content of free fatty acids, sulphurs and terpenes compounds. Moreover, in ricotta a higher VOC concentration was observed compared to the curd, probably due to the high temperature required during the ricotta process. The effect of the progressive nutrient depletion of milk was investigated by contrasts between VOC concentration of milk in the vat, whey, and scotta. Although milk contains a greater amount of nutrients, whey and scotta have shown a higher concentration of VOCs with the exceptions of esters, sulphurs, terpenes and phenolic compounds. Finally, the effect of ripening was tested by comparing the quantity of VOCs of curd and of aged cheeses (6 and 12 months). The release of volatile compounds increased with increasing ripening period in relation with the enzymatic and microbiological activity of cheese. In summary, the spectrometric techniques (SPME/GC-MS and PTR-ToF-MS) used in this work demonstrated to be very efficient to characterize the volatile organic compounds of dairy products. The dairy system, and cow related factors affected the volatile fingerprint of ripened cheeses. Particularly, concerning the individual animal source of variation, lactation stage was the most important effect followed by the cow’s parity and the milk yield. On the basis of phenotypes used in this work, the traits collected offered the potential for a genetic analysis to be carried out. The genetic analysis demonstrated the existence of an exploitable genetic variability of the volatile profile of cheese that might be useful for an (in)direct selection of dairy cows for cheese quality traits in breeding programs. Nevertheless, further research is needed in this area. In the era of genomics for e.g., it might be interesting to associate genomic regions to specific VOCs. This information might be useful for genomic breeding programs. The evolution of volatile compounds across the production chain depends on specific technological aspects, such as the process of natural creaming, the temperature of coagulation, and the ripening period. The monitoring of volatile fingerprint permits to obtain dairy products with specific organoleptic characteristics useful to differentiate them on the market and to improve the supply chain efficiency on the basis of quality aspects.
Negli ultimi anni, il consumatore è diventato sempre più sensibile agli aspetti qualitativi degli alimenti, i quali sono fortemente influenzati dalle caratteristiche sensoriali come l’aroma. Diversi lavori scientifici hanno dimostrato che i composti volatili (VOCs) rilasciati dall’alimento sono correlati con il suo aroma e possono essere considerati come traccianti delle filiere alimentari. Oggi, l’analisi dei VOCs richiede strumenti rapidi, sensibili, non invasivi e che abbiano bisogno dell’impiego di pochi solventi durante la preparazione del campione. E’ stato dimostrato che i VOCs possono essere estratti, misurati e identificati con la Gas Cromatografia di Massa (GC-MS) senza pre-concentrazioni o pre-trattamenti dell’alimento da analizzare. Gli obiettivi principali della tesi di dottorato erano di studiare la presenza di composti volatili nei prodotti lattiero-caseari. Più precisamente, questo studio aveva come obiettivi di i) qualificare e quantificare i VOCs nei prodotti lattiero-caseari, ii) esaminare la loro formazione e iii) integrare le conoscenze acquisite su questi composti attraverso tutta la filiera di produzione dalla materia prima fino al prodotto finito. Inoltre, analisi statistiche sono state utilizzate per collegare i VOCs con la caratterizzazione genetica degli animali, il sistema di allevamento e le caratteristiche individuali delle vacche (es. stadio di lattazione, ordine di parto e produzione giornaliera di latte). L’identificazione e la quantificazione dei VOCs sono state fatte utilizzando tecniche analitiche precise, veloci e non invasive (Solid Phase Micro Extraction/Gas Chromatography-Mass Spectrometry SPME/GC-MS and Proton Transfer Reaction-Time of Flight-Mass Spectrometry PTR-ToF-MS). Per rispondere agli obiettivi generali della tesi, l’attività di ricerca è stata divisa in cinque parti connesse tra di loro. L’obiettivo nel primo capitolo era di studiare i composti volatili presenti nello spazio di testa di campioni di formaggio. Per questo scopo, sono stati analizzati 150 formaggi stagionati per due mesi. I formaggi sono stati prodotti utilizzando una metodica di caseificazione individuale usando latte individuale di vacche di razza Bruna. Gli animali sono stati allevati in 30 aziende appartenenti a diversi sistemi di allevamento, da tradizionale (tipico della realtà montana) a moderno. In questo studio sono stati identificati 55 VOCs per ogni formaggio, classificati in diverse famiglie chimiche: acidi grassi, esteri, alcoli, aldeidi, chetoni, lattoni, terpeni e pirazine. Dai risultati emerge che il sistema di allevamento e le caratteristiche individuali delle vacche (stadio di lattazione, ordine di parto e produzione giornaliera di latte) influenzano i composti volatili. Inoltre, per testare la riproducibilità dello strumento e della metodica di caseificazione; la data di analisi cromatografica, l’ordine d’iniezione del campione nello strumento (GC), e la caldaia di caseificazione erano inclusi nel modello statistico. In molti casi, questi fattori analitici/strumentali non influenzano la quantità di VOCs rilasciata dai formaggi. Nel secondo capitolo, il potenziale di una nuova tecnica analitica (PTR-ToF-MS) è stato approfondito per studiare, su larga scala, le caratteristiche qualitative del formaggio. Il PTR-ToF-MS dal punto di vista analitico, permette un’iniezione diretta del campione senza estrazione o pre-concentrazione, ha un breve tempo di analisi (solo pochi secondi per campione) e grande sensibilità consentendo di monitorare in tempo reale l’evoluzione dei composti volatili. L’analisi produce uno spettro molto dettagliato che può essere utile per la caratterizzazione delle qualità e della tipicità dell’alimento. In particolare, è stata analizzata l’impronta aromatica di 1,075 formaggi prodotti utilizzando latte individuale di vacche di razza Bruna allevate in 72 aziende appartenenti a diversi sistemi di allevamento. L’impronta aromatica (spettro) era caratterizzata da più di 600 picchi (variabili) per ogni formaggio. Gli spettri sono stati analizzati e dopo la rimozione degli ioni interferenti e del rumore di fondo è stato selezionato un data set costituito da 240 picchi per ogni formaggio. In seguito, basandosi sui risultati del primo contributo e sulla letteratura sono stati identificati i picchi più importanti (61) in termini quantitativi e qualitativi. Per sintetizzare la quantità di informazioni ovvero estrarre delle componenti principali (PC) è stata fatta un’analisi multivariata (PCA) a partire dai 240 picchi spettrometrici. In seguito, le PCs sono state caratterizzate sulla base delle loro correlazioni con i 240 picchi spettrometrici. Sono stati analizzati gli effetti del sistema di allevamento, dell’azienda entro sistema di allevamento, le caratteristiche individuali delle vacche (stadio di lattazione, ordine di parto e produzione di latte), e caldaia di caseificazione sulle PCs e sui 240 picchi. Dai risultati emerge che il sistema di allevamento è correlato con le PC e 57 picchi, specialmente quando le aziende come tecnica di alimentazione utilizzano il carro miscelatore (TMR) con e senza insilati nella dieta. Considerando le caratteristiche individuali delle vacche, l’effetto più significativo è lo stadio di lattazione (139 picchi), seguito dalla produzione di latte e dall’ordine di parto, con 31 e 21 picchi, rispettivamente. Infine, la caldaia di caseificazione è un effetto spesso non significativo, confermando la buona riproducibilità della micro-caseificazione utilizzata anche per lo studio di aspetti qualitativi del formaggio. Nel terzo capitolo è stato studiato l’effetto della genetica dell’animale sui composti volatili dei formaggi. A tale scopo, sono state analizzate le componenti principali (estratte come discusso sopra nel secondo contributo) e i 240 picchi spettrometrici (PTR-ToF-MS) utilizzando un modello animale con un approccio Baesiano. Dai risultati emerge in media un’ereditabilità (h2) del 7 % per le componenti principali, la quale è simile all’h2 trovata per le cellule somatiche e leggermente più bassa di quella del contenuto di grasso nel latte e della produzione giornaliera di latte stimate in precedenza sugli stessi animali. E’ interessante osservare che solo una piccola quantità di picchi ha una bassa h2 (<7%). La maggior parte di essi presenta valori simili a quelli trovati per le PCs, mentre 40 picchi presentano ereditabilità simile a quella trovata per la produzione giornaliera di latte e ad altre caratteristiche qualitative del latte. La variabilità attribuita all'azienda è risultata diversa per le PCs. Questi risultati dimostrano che esiste un’interessante variabilità genetica di alcuni VOCs che potrebbe essere potenzialmente utilizzata nei programmi di miglioramento genetico. L’obiettivo nel quarto capitolo era di studiare l’effetto della transumanza sulle caratteristiche qualitative di prodotti lattiero-caseari. Vista la grande mole di dati, questo contributo è stato diviso in due parti tra loro connesse. Nella prima parte è stata studiata l’evoluzione della qualità del latte e del formaggio, mentre nella seconda parte è stata analizzata l’evoluzione dei composti volatili dei prodotti lattiero-caseari nel processo di caseificazione. Nella prima parte, sono state analizzate le proprietà fisiche, chimiche e tecnologiche di 11 prodotti lattiero-caseari raccolti durante la transumanza al pascolo Alpino (Malga) di vacche da latte. E’ risaputo che i prodotti ottenuti durante il periodo di alpeggio possono avere un valore aggiunto dovuto alle elevate proprietà nutrizionali, salutistiche e aromatiche. Per approfondire le conoscenze finora acquisite, è stata fatta questa prova in cui è stato utilizzato il latte di massa prodotto da 148 vacche allevate giorno e notte al pascolo (1,860 m s.l.m.). Durante l’esperimento, sono state fatte 7 caseificazioni seguendo tecniche tradizionali, una ogni 2 settimane, utilizzando il latte prodotto durante la transumanza (da giugno a settembre). Sono stati raccolti per ogni caseificazione: il latte della mungitura della sera (giorno prima della caseificazione), lo stesso latte il mattino successivo (dopo il processo di scrematura naturale), la panna di affioramento, il latte della mungitura del mattino, il latte in caldaia ottenuta dalla miscela tra il latte scremato della mungitura della sera con il latte della mungitura del mattino, la cagliata, il siero, la ricotta ottenuta dal siero e il residuo della lavorazione ossia la scotta. Inoltre, la cagliata è stata usata per produrre formaggi di “Malga” che sono stati stagionati per 6 e 12 mesi. Le caratteristiche chimico-fisiche sono state misurate con una tecnologia a infrarosso. I risultati dimostrano una variazione della produzione giornaliera e composizione chimica del latte, resa in formaggio e recupero/o perdita di nutrienti nel processo di caseificazione tradizionale. In particolare, si è osservata una riduzione della produzione giornaliera di latte, grasso, proteine e lattosio del latte durante la transumanza estiva. Tuttavia, si è anche osservato un effetto positivo sulla produzione e la composizione chimica del latte del ritorno delle vacche nelle aziende di fondo valle alla fine della stagione dell’alpeggio. La resa media di formaggio in questo lavoro è risultata del 14.2%, mentre i recuperi di grasso, proteine, solidi totali ed energia sono del 85.1%, 77.8%, 49.4% e 58.1%, rispettivamente. Questi risultati sono in linea con quelli trovato in letteratura. Nella seconda parte di questo contributo, è stato misurato il contenuto di composti volatili nello spazio di testa dei campioni con la tecnica SPME/GC-MS. Dopo l’analisi, sono stati identificati 49 VOCs appartenenti alle famiglie chimiche degli alcoli, aldeidi, acidi grassi, chetoni, esteri, lattoni, terpeni e composti solforati e fenolici. Inoltre, è stata studiata l’evoluzione dei VOCs e delle loro famiglie chimiche attraverso i processi di caseificazione, di produzione della ricotta e di stagionatura del formaggio. Il confronto tra la concentrazione dei VOCs dei 4 tipi di latte (intero e scremato della sera, intero del mattino, caldaia) ha dimostrato che il processo di scrematura influenza la concentrazione di metà dei composti volatili analizzati, seguito dall’effetto della mungitura (intero della sera vs. intero del mattino) e dall’effetto del mescolamento (latte scremato della sera mescolato in parti uguali con il latte del mattino). In generale, la panna, rispetto a cagliata e ricotta, ha un maggiore contenuto di acidi grassi, terpeni e composti solforati. Inoltre, la ricotta rispetto alla cagliata ha un’elevata concentrazione di VOC, probabilmente dovuta alla maggiore temperatura utilizzata durante il processo di produzione. L’effetto del progressivo depauperamento di nutriente del latte è stato studiato attraverso il confronto tra latte in caldaia, siero e scotta. Sebbene il latte abbia un maggiore contenuto di nutrienti, il siero e la scotta hanno una maggiore concentrazione di VOC ad eccezione delle famiglie chimiche degli esteri, terpeni, composti solforati e fenolici. Infine, l’effetto della maturazione è stato valutato attraverso il confronto tra le quantità di VOC della cagliata e dei formaggi stagionati (6 e 12 mesi). Il rilascio dei composti volatili incrementa con l’aumento del periodo di maturazione probabilmente dovuto a una maggiore attività enzimatica e microbiologica nel formaggio. In conclusione, le tecniche analitiche di spettrometria di massa utilizzate in questo lavoro (SPME/GC-MS e PTR-ToF-MS) hanno permesso di caratterizzare i composti volatili dei prodotti lattiero-caseari in maniera efficiente. Il sistema di allevamento, le caratteristiche individuali delle vacche hanno influenzato l’impronta aromatica di formaggi individuali stagionati. In particolare, riguardo alle caratteristiche individuali degli animali il principale effetto era lo stadio di lattazione seguito da ordine di parto e produzione giornaliera di latte. Sulla base dei fenotipi raccolti in questo lavoro è stato possibile effettuare un’analisi genetica, la quale ha dimostrato l’esistenza di un’interessante variabilità genetica connessa ai composti volatili del formaggio che potrebbe essere utile per una selezione (in)diretta delle vacche da latte sulla base di aspetti qualitativi in programmi di miglioramento genetico. Tuttavia sono necessarie altre ricerche in quest’area per esempio, nell’era della genomica, sarebbe interessante associare qualche regione specifica del genoma ai composti volatili. L’evoluzione dei composti volatile attraverso la filiera di produzione dipende da specifici aspetti tecnologici, come l’affioramento della panna, la temperatura di coagulazione e il periodo di stagionatura. Il monitoraggio dell’impronta aromatica permette di ottenere prodotti lattiero-caseari con delle specifiche caratteristiche organolettiche utili a differenziare il prodotto sul mercato e a migliorare l’efficienza dell’intera filiera produttiva sulla base di aspetti qualitativi.

The current study aims to contribute to better address the knowledge about the aging processes of wood and its modifications, but, what is more, it includes the use of volatile organic compounds (VOCs) analysis to provide evidence of aging processes and to monitor degradation progress, in order to identify the causes of damage of wood-based-material or even wood artefacts. To this aim, different experiments, both of spectroscopic characterization and emission analysis, on the chemical structure of aged wood were carried out, supplemented with investigations on recent wood and a thorough literature review.

In recent years, consumers have become increasingly interested in the quality aspects of food. Food quality, in turn, is strongly related to the sensory characteristics such as the flavor. Several scientific studies have shown that the Volatile Organic Compounds (VOCs) released by the food are related to the flavor and can be considered as assistive markers in the production chain. Today, the analysis of VOCs requires fast, non-invasive, and solvent free devices. It has been shown that the VOCs can be extracted, identified, and measured with a Gas ChromatographyMass Spectrometry (GC-MS) without any pre-concentration or pre-treatment of the food. The main objective of this PhD thesis was to investigate the presence of volatile compounds in dairy products. More precisely, this study aimed in i) qualifying and quantifying VOCs in dairy products, ii) examining their formation and iii) integrating knowledge on VOCs by tracking their release during the whole production process from the raw materials till the final dairy product. In addition, statistical analysis was applied to link VOCs with the genetic characterization of animals, dairy system and individual cow-factors (e.g. stage of lactation, order of parity and milk yield). The identification and quantification of VOCs were performed using fast and non-invasive analytical approaches (Solid Phase Micro Extraction/Gas Chromatography-Mass Spectrometry SPME/GC-MS and Proton Transfer Reaction-Time of Flight-Mass Spectrometry PTR-ToF-MS) that can monitor the evolution of VOCs. To achieve the overall goal, the research was partitioned in four interrelated subparts as described below. The aim of the first chapter was to study the VOCs presence in the headspace of cheese. To this purpose, 150 cheeses ripened for two months were used. The cheeses were obtained through an individual model cheese-making approach using milk from individual Brown Swiss cows. Animals reared in 30 herds belonging to different dairy systems, from traditional (typical of the mountainous area) to modern ones. The study identified 55 VOCs classified in the chemical families of free fatty acids, esters, alcohols, aldehydes, ketones, lactones, terpenes, and pyrazines. We found that dairy system and individual cow characteristics (lactation stage, order of parity and daily milk yield) influenced the volatile compounds. In order, to test the instrument reproducibility and the model cheese-making procedure; data of GC analysis, order of injection of the sample into instrument, and vat were included in the statistical model. In many cases, these analytical factors did not affect the amount of VOCs released by cheese. In the second chapter, the potential of a new spectrometric technique (PTR-ToF-MS) was investigated to study cheese quality traits on a large scale. The PTR-ToF-MS allows direct injection of the sample headspace without extraction or pre-concentration steps, has a shorter analysis time (only a few seconds per sample) and greater sensitivity that permit to monitor on-line the evolution of volatile compounds. The resulting spectral information can provide a very detailed description of samples, which is useful for characterizing food quality and typicality. In particular, we analyzed the volatile fingerprint of 1,075 model cheeses produced using individual milk of Brown Swiss cows reared in 72 herds of different dairy systems. The output of PTR (spectrum) was characterized by more than 600 spectrometric peaks (variables). After removing interfering ions and background noise a set of 240 peaks was selected. Further, based on the results of the first contribution and literature, 61 peaks were identified. These peaks represent the major part of the cheese flavor. To summarize the amount of information, a multivariate analysis (PCA) was applied associating principal components (PC) with the 240 spectrometric peaks. Following, we tried to characterize the PCs through the correlations between PCs and the spectrometric peaks. The effects of dairy system, herd within dairy system, individual cows characteristics (lactation stage, order of parity and milk yield), and vat used for the cheese-making on the PCs and on the 240 peaks were analyzed. Dairy system was correlated with PC and 57 spectrometric peaks, especially when the herds were using Total Mixer Ration (TMR) as feeding technique, including or not maize silage in the diets. Regarding the individual animal characteristics, the most significant effect was the stage of lactation (139 peaks), followed by milk yield and parity, with 31 and 21 peaks, respectively. Finally, the vat used for the cheese-making was not found to be significant, confirming the good reproducibility of the model cheese-making procedure used to study cheese quality aspects. In the third chapter, the effect of cows’ genetics to the VOCs of ripened cheeses was assessed. Principal components and the 240 spectrometric peaks (as described above in the second contribution) were used fitting an animal model in a Bayesian framework. On average, heritability (h2) of 7% for PCs was found, which is similar to h2 of somatic cell count and much lower than the h2 of milk fat content and daily milk yield. It is interesting to note that only a small proportion of peaks showed very low h2 (<7%). The major part of them showed values similar to those found for PCs, while forty peaks presented heritability similar to that of milk yield and other milk quality traits. The variability attributed to the herd was different for the various PC. Results suggest a potential of improvement for several cheese VOCs through genetic selection in dairy cow breeding programs. The aim of the fourth chapter was to study the effect of summer transhumance on the quality traits of dairy products. Due to the extended work, this contribution was further splitted into two parts. In the first part, the evolution of milk and cheese quality characteristics were studied, while in the second part the evolution of VOC content of dairy products was analyzed. For the first part, chemical characteristics and technological properties of 11 dairy products obtained during summer transhumance of cows to Alpine pastures (Malga) were analyzed. Dairy products obtained throughout this period are known to give origin to high-value, healthier products, and extra tasty,. Bulk milk from 148 dairy cows reared day and night on Alpine pasture (1,860 m a.s.l.) was used. We performed 7 experimental cheese-making according to traditional mountain techniques, one every two weeks, using milk produced during the summer transhumance (from June to September). For each cheese-making we collected: milk from the evening milking (day before the cheese-making), the same milk the following morning (after natural creaming), the cream separated, the whole milk from the morning milking, the milk in vat obtained mixing the creamed evening milk with the whole morning milk, the fresh curd, the whey, the ricotta obtained from whey, and the residual scotta. Moreover, the curd was used to produce typical “Malga” cheese that was ripened for 6 and 12 months. The chemical characteristics were measured with infrared technology. Results highlighted variation in milk yield, milk chemical composition, cheese yield and curd recoveries and/or loss of nutrients in the traditional cheese-making. In particular, a reduction of milk yield, fat, protein and lactose contents of milk during summer transhumance was observed. Nevertheless, the return to lowland farming systems of the cows at the end of grazing season, positively affected milk yield and milk chemical composition. The average of cheese yield was 14.2%, while recoveries of fat, protein, total solids and energy were 85.1%, 77.8%, 49.4% and 58.1%, respectively. These results were in accordance to those found in the literature. For the second part of this chapter, the VOCs content of sample headspace was measured through SPME/GC-MS. Forth nine VOCs belonging to the chemical families of alcohols, aldehydes, free fatty acids, ketones, esters, lactones, terpenes, phenolic, and sulphur compounds were detected. In addition, the evolution of VOCs and their chemical family across the cheese- and ricotta-making processing as well as during the cheese ripening period was tracked. The comparison between VOCs concentration of 4 types of milk (whole evening, creaming milk, whole morning, milk in vat) showed that the creaming process significantly affected about half of all the volatile organic compounds analyzed, followed by the effects of milking (evening milking vs. morning milking) and the mixing (creamed milk mixed with whole morning milk). In general, the cream, in contrast to curd and ricotta, showed higher content of free fatty acids, sulphurs and terpenes compounds. Moreover, in ricotta a higher VOC concentration was observed compared to the curd, probably due to the high temperature required during the ricotta process. The effect of the progressive nutrient depletion of milk was investigated by contrasts between VOC concentration of milk in the vat, whey, and scotta. Although milk contains a greater amount of nutrients, whey and scotta have shown a higher concentration of VOCs with the exceptions of esters, sulphurs, terpenes and phenolic compounds. Finally, the effect of ripening was tested by comparing the quantity of VOCs of curd and of aged cheeses (6 and 12 months). The release of volatile compounds increased with increasing ripening period in relation with the enzymatic and microbiological activity of cheese. In summary, the spectrometric techniques (SPME/GC-MS and PTR-ToF-MS) used in this work demonstrated to be very efficient to characterize the volatile organic compounds of dairy products. The dairy system, and cow related factors affected the volatile fingerprint of ripened cheeses. Particularly, concerning the individual animal source of variation, lactation stage was the most important effect followed by the cow’s parity and the milk yield. On the basis of phenotypes used in this work, the traits collected offered the potential for a genetic analysis to be carried out. The genetic analysis demonstrated the existence of an exploitable genetic variability of the volatile profile of cheese that might be useful for an (in)direct selection of dairy cows for cheese quality traits in breeding programs. Nevertheless, further research is needed in this area. In the era of genomics for e.g., it might be interesting to associate genomic regions to specific VOCs. This information might be useful for genomic breeding programs. The evolution of volatile compounds across the production chain depends on specific technological aspects, such as the process of natural creaming, the temperature of coagulation, and the ripening period. The monitoring of volatile fingerprint permits to obtain dairy products with specific organoleptic characteristics useful to differentiate them on the market and to improve the supply chain efficiency on the basis of quality aspects.

Given the ubiquity of limonene in cleaning and cosmetic products, investigating its gasphase oxidation products from reactions with OH radicals and ozone has become important for human health. The present study investigates limonene gas-phase reaction with OH radicals under controlled NOx or NOx-free conditions using facilities from the 760 L Environmental Simulation Chamber made of Quartz (ESC-Q-UAIC) together with state-of-the-art instruments such as proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS, model 6000 X2, IONICON). The obtained kinetic results (klimonene+OH = (16.42 � 2.20) ? 10-11 cm3?molecule-1?s-1), based on the relative rate techniques with 1,3,5-trimethylbenzene and cyclohexene as reference compounds, are in good agreement with the previous kinetic studies. The PTR-ToF-MS mass spectra acquired within the NOx-free experiments revealed signals at mass-to-charge ratios of 101.060, 139.112, and 169.122, that may be assigned to potentially harmful oxidation products, namely 4-oxopentanal (C5H8O2), 4-acetyl-1-methylcyclohexene (C9H14O), and 3-isopropenyl-6-oxo-heptanal (C10H16O2), respectively. Additionally, observed differences between NOx and NOx-free experiments highlight that NOx strongly suppresses the formation of secondary organic aerosols during limonene oxidation and favours the formation of 4-acetyl-1-methylcyclohexene.