The good, the bad and the aged: Predicting sensory quality of anhydrous milk fat by PTR/SRI-Tof-MS analysis and data mining

Revealing dynamic changes of the volatile profile of food samples using PTR-MS

Volatile compounds carry valuable information regarding the properties of foodstuffs. Volatiles emitted from food can be used as, for example, indicators of quality, shelf-life, or authenticity. A better understanding of the multitude of transformations which occur during food processing could facilitate the optimisation of production, increase the desirability of food products, and also their wholesomeness. However, as some of these transformations are fast-paced, it is necessary to monitor them using techniques which enable real-time determination of volatiles, such as proton transfer reaction-mass spectrometry (PTR-MS). Recent years have seen a marked increase in its use in food analysis, since it can be used to obtain insight into the dynamics of the monitored processes and can be the basis for precise quality control methods for food processing. This review highlights recent works in which PTR-MS was used in monitoring during foodstuffs production, preparation and storage.

Nonuniform Electric Field-Enhanced In-Source Declustering in High-Pressure Photoionization/Photoionization-Induced Chemical Ionization Mass Spectrometry for Operando Catalytic Reaction Monitoring

Photoionization mass spectrometry (PI-MS) is a powerful and highly sensitive analytical technique for online monitoring of volatile organic compounds (VOCs). However, due to the large difference of PI cross sections for different compounds and the limitation of photon energy, the ability of lamp-based PI-MS for detection of compounds with low PI cross sections and high ionization energies (IEs) is insufficient. Although the ion production rate can be improved by elevating the ion source pressure, the problem of generating plenty of cluster ions, such as [MH]⁺·(H₂O)_n (n = 1 and 2) and [M₂]⁺, needs be solved. In this work, we developed a new nonuniform electric field high-pressure photoionization/photoionization-induced chemical ionization (NEF-HPPI/PICI) source with the abilities of both HPPI and PICI, which was accomplished through ion-molecule reactions with high-intensity H₃O⁺ reactant ions generated by photoelectron ionization (PEI) of water molecules. By establishing a nonuniform electric field in a three-zone ionization region to enhance in-source declustering and using 99.999% helium as the carrier gas, not only the formation of cluster ions was significantly diminished, but the ion transmission efficiency was also improved. Consequently, the main characteristic ion for each analyte both in HPPI and PICI occupied more than 80%, especially [HCOOH·H]⁺ with a yield ratio of 99.2% for formic acid. The analytical capacity of this system was demonstrated by operando monitoring the hydrocarbons and oxygenated VOC products during the methanol-to-olefins and methane conversion catalytic reaction processes, exhibiting wide potential applications in process monitoring, reaction mechanism research, and online quality control.