Photoionization of Benzophenone in the Gas Phase: Theory and Experiment

Integrating density functional theory and chemical ionization mass spectrometry techniques to assess benzophenone derivatives in food packaging: implications for enhancing food quality and safety

Benzophenone and related derivatives are widely used as photoinitiators for food packaging to cure inks or lacquers with ultraviolet (UV) light on cardboard and paper. However, there are concerns about the potential health risks of their migration into food. Knowing the physical and chemical properties of benzophenone and its derivatives could play a significant role in their quantification and analysis using chemical ionization mass spectrometry (CI-MS) methods. These parameters are evaluated using B3LYP/6-311++** density functional theory (DFT) implemented on Gaussian code. Ion-molecule chemistry through the selection of reagent ions, reaction energetics and kinetics, thermodynamic stability, and reactivity of molecules deemed to foster VOC identification and quantification via CI-MS techniques. The VOCs under study are expected to undergo exothermic reactions from H3 O+ , NH4 + , NO+ , and O2 + ions, except endothermic proton transfer from NH4 + to 2-hydroxy-4-methoxybenzophenone and 2,3,4-trihydroxy benzophenone. These compounds possess less proton affinities than NH3 and are least stable in their protonated forms. The DFT computed properties provide the basis for developing reliable and accurate methods to detect and measure the presence of benzophenone and its derivatives in packaging materials and food products.

Energetics and ionization dynamics of two diarylketone molecules: benzophenone and fluorenone

Single photon ionization and subsequent unimolecular ion decomposition were studied on jet-cooled benzophenone and fluorenone separately, using VUV synchrotron radiation in a photoion/photoelectron coincidence setup. Slow PhotoElectron Spectra (SPES) were recorded in coincidence with either the parent or the fragment ions for hν < 12.5 eV. Dissociative ionization is observed for benzophenone only. The full interpretation of the measurements, including the identification of the neutral and ionic species when dissociative ionization is at play, benefits from high level ab initio computations for determining the equilibrium structures and the energetics of the neutral and ionized molecules and of their fragments. Electronically excited states of the parent molecular ions were calculated also. From this analysis, an accurate experimental determination of the energetics of the benzophenone and fluorenone ions and of their fragmentation channels is available: adiabatic ionization energies of benzophenone at 8.923 ± 0.005 eV and of fluorenone at 8.356 ± 0.007 eV; and appearance energies of benzophenone fragment ions at 11.04 ± 0.02 eV (loss of C₆H₅), 11.28 ± 0.02 eV (loss of H) and 11.45 ± 0.02 eV (loss of CO). The corresponding fragmentation mechanisms are explored, showing likely concerted bonds rearrangement. Possible pre-ionizing fragmentation is discussed in light of the spectra presented. The structural rigidity of fluorenone diarylketone seems to be the origin of the inhibition of the fragmentation of its cation.