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We compute the proton transfer rates to a range of volatile organic compounds (VOCs) related to cork taint in wine. These rates are useful to support quantification in proton-transfer-reaction mass spectrometry (PTR-MS) and in selected-ion flow-tube mass spectrometry (SIFT-MS). We apply the average dipole orientation theory and the parameterized trajectory method to evaluate the rate coefficients for proton transfer occurring in ion-molecule collision, from both H 3 O + and NH + 4 to the VOCs. The main input ingredients for these methods are the electric dipole moment and polarizability of the VOC molecules, which we evaluate by means of quantum chemical calculations based on density functional theory. We provide new data for proton transfer rate coefficients of compounds responsible for cork taint and off-flavor in wine such as chloroanisoles, bromoanisoles, methylisoborneol, guaiacol, and terpenes.

Density-functional theory (DFT) is used to obtain the molecular data essential for predicting the reaction kinetics of chemical-ionization-mass spectrometry (CI-MS), as applied in the analysis of volatile organic compounds (VOCs). We study charge-transfer reactions from NO+ and O2 + reagent ions to VOCs related to cork-taint and off-flavor in wine. We evaluate the collision rate coefficients of ion–molecule reactions by means of collision-based models. Many NO+ and O2 + reactions are known to proceed at or close to their respective collision rates. Factors affecting the collision reaction rates, including electric-dipole moment and polarizability, temperature, and electric field are addressed, targeting the conditions of standard CI-MS techniques. The molecular electric-dipole moment and polarizability are the basic ingredients for the calculation of collision reaction rates in ion–molecule collision-based models. Using quantum-mechanical calculations, we evaluate these quantities for the neutral VOCs. We also investigate the thermodynamic feasibility of the reactions by computing the enthalpy change in these charge-transfer reactions.

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