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

Abstract

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.