Real-Time Proton Transfer Reaction Mass Spectrometry for Pesticide Detection: A DFT-Based Feasibility Evaluation

This feasibility study evaluates the application of proton transfer reaction mass spectrometry (PTR-MS) for the online measurement of pesticides. Although PTR-MS has established its efficacy in detecting volatile organic compounds, its potential for pesticide detection remains underexplored. DFT calculations were performed at the B3LYP/6-311++G(d,p) level to predict essential molecular properties, including dipole moments, polarizabilities, proton affinities, and ionization energies. These calculations provided insights into the thermodynamics of ion-molecule reactions, revealing that most pesticides exhibit favorable ionization reactions with H₃O⁺ and NO⁺, whereas NH₄ ⁺ may present challenges for certain compounds like fenitrothion. Additionally, we calculated ion-molecule reaction rate constants, which facilitate quantification without prior standard calibration. This study lays the groundwork for the future development of real-time pesticide residue monitoring techniques based on PTR-MS, with potential application in food safety and environmental monitoring.