Theoretical Investigation of Charge Transfer from NO+ and O2+ Ions to Wine-Related Volatile Compounds for Mass Spectrometry

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 O-2(+) 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 O-2(+) 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.

Automated summary

This study applies density-functional theory (DFT) to obtain molecular data for predicting the reaction kinetics of chemical-ionization-mass spectrometry (CI-MS) in the analysis of volatile organic compounds (VOCs). The collision rate coefficients of ion-molecule reactions are evaluated using collision-based models. Factors affecting collision reaction rates, including electric-dipole moment and polarizability, temperature, and electric field, are investigated. Molecular electric-dipole moment and polarizability are determined for neutral VOCs to calculate collision reaction rates. The thermodynamic feasibility of the reactions is also examined by computing the enthalpy change.