[Cappellin2010] "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.
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.
[Spitaler2007] "PTR-MS in enology: Advances in analytics and data analysis",
International Journal of Mass Spectrometry
, vol. 266, no. 1: Elsevier, pp. 1–7, 2007.
The present communication deals with the improvement of proton transfer reaction mass spectrometry (PTR-MS) wine headspace analyses. In contrast to previous PTR-MS investigations of wine, where wine headspace was ionized by protonated ethanol clusters, the headspace was diluted by a factor of 1:40 with N2 and ionized by H3O+ ions. This method is better suited for routine applications than the previously reported method since it is simpler, faster, and the mass spectra obtained are less complex. A test wine was mixed with ethanol and with water to yield ethanol contents ranging from 10 to 15% (v/v) and these mixtures were analyzed to assess whether any quantitative differences in the composition of volatiles were detectable. The data showed no impact of the ethanol content on the wine headspace composition. The new method was applied to eight different wine samples produced from two different grape varieties: Pinot Noir and Cabernet Sauvignon. Each variety was grown in two different locations in South Tyrol (Northern Italy) and harvested at two different dates. Quantitative (but not qualitative) differences in PTR-MS spectra between the two wine varieties were observed. Using principal component analysis of selected m/z signals differentiation between Pinot Noir and Cabernet Sauvignon samples was achievable.
[Biasioli2011a] "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.
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.
[Aprea2007] "PTR-MS study of esters in water and water/ethanol solutions: Fragmentation patterns and partition coefficients",
International journal of mass spectrometry
, vol. 262, no. 1: Elsevier, pp. 114–121, 2007.
Esters strongly influence the perceived aroma of alcoholic beverages and their rapid monitoring can play an important role in the quality control of these products. Proton transfer reaction mass spectrometry (PTR-MS) allows the rapid and non invasive monitoring of foodstuff but there is still a lack of information about the proton transfer induced fragmentation and on the effect of high ethanol concentration. PTR-MS fragmentation patterns of 21 esters are reported, most of them for the first time. For linear methyl and ethyl esters the fragmentation dependence on E/N was also evaluated. Acetate esters, with exception of methyl acetate, show as main peaks the characteristic fragment ions at m/z 61 and m/z 43, whereas propanoate esters, but methyl propanoate, exhibit as main peaks the typical signals at m/z 75 and m/z 57. For all the other esters, here reported, the spectra are dominated by the protonated molecular ion. For methyl and ethyl esters we also report, in many cases for the first time, the water-solution/air partition coefficients (Henry's law constant) and the ethanol-solution/air partition coefficients at different ethanol concentrations. The information provided in this work may be useful as a basis for further studies for the identification and quantification of esters in the headspace of alcoholic beverages extending the application field of PTR-MS.