AB-INITIO CALCULATION OF THE RATES OF THE REACTIONS BETWEEN VOLATILE ORGANIC COMPOUNDS IN WINE AND CATIONS FOR MASS SPECTROMETRY
Tesi di Dottorato
Data di Pubblicazione:
2020
Citazione:
AB-INITIO CALCULATION OF THE RATES OF THE REACTIONS BETWEEN VOLATILE ORGANIC COMPOUNDS IN WINE AND CATIONS FOR MASS SPECTROMETRY / M. Kumar ; coordinatore: M. Paris ; co-supervisore: P. Pisieri, F. Biasioli ; supervisore: N. Manini. Dipartimento di Fisica Aldo Pontremoli, 2020 Dec 18. 33. ciclo, Anno Accademico 2020. [10.13130/kumar-manjeet_phd2020-12-18].
Abstract:
Wine is a complex mixture housing many aroma and flavor compounds giving it a unique
texture and bouquet. These volatile organic compounds (VOCs), if present near the sensory
threshold limits, may contribute positively to wine quality; however, excessive amounts can
detract from quality, and are considered as a fault in wine. It is believed that nearly 10% of
the world’s wine is affected from various types of faults.
The most common and potent wine taint is 2,4,6-trichloroanisole (2,4,6-TCA), commonly known as cork-taint molecule resulting from the cork stopper of wine bottles. 2,4,6-
TCA produces intense ’musty’, ’mouldy’ ’earthy’ smelling in wine.
Similar off-flavor smells are associated to compounds including geosmin and 2-methoxy-
3,5-dimethylpyrazine. We studied 74 such VOCs frequently present in wine. Determining
concentration of VOCs in wine requires detection techniques to be fast, in real time, and
with a detection limit as low as few parts per trillion by volume. The most frequently used
techniques based on direct injection mass spectrometry, namely proton transfer reaction
mass spectrometry (PTR-MS) and selected ion flow tube mass spectrometry (SIFT-MS),
are being successfully employed in the measurements of VOCs concentrations.
Quantification using these techniques usually relies on compound-by-compound instrument calibration. The calibration procedures are generally laborious and time-consuming.
The theoretical evaluation of the rate coefficients of ion-molecule reactions occurring in
PTR-MS/SIFT-MS flow (drift) tubes is a practical alternative to calibration.
In this thesis, we compute and report the rate coefficients for ion-molecule reactions,
relevant for different experimental conditions, such as varied temperature and electric fields
inside the drift tube. We have used well-established models based on capture cross-section
collision and classical trajectories. These models rely on physical properties such as electric dipole moment and polarizability of the volatile molecules. To compute these quantities
we resorted to ab initio density functional theory.
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
M. Kumar
Link alla scheda completa: