Development and Application of a New QuEChERS Method Coupled with UPLC-QTOF-MS/MS for Analysis of Tiafenacil and Its Photolysis Products in Water

This research centered on the novel pyrimidinedione herbicide, tiafenacil. Residues of tiafenacil and its three photolysis products (PP1 to PP3) in water were analyzed using advanced QuEChERS and UPLC-QTOF-MS/MS techniques, reaching a low limit of quantitation (LOQ) of 10 μg/L. Calibration curves exhibited a high degree of linearity (<i>R</i>² ≥ 0.993) over a concentration range of 0.01 to 1.00 mg/L. Method validation demonstrated high precision, with intraday relative standard deviation RSDr ≤7.9% and interday RSD_R ≤ 6.1%, along with high accuracy (recoveries from 94.4% to 105.0%). Using density functional theory (DFT) at the B3LYP/6-311g (d) level, we calculated the electronic properties of tiafenacil and its PPs (PP1 to PP3). Additionally, frontier molecular orbital (FMO) and fukui function analyses were conducted to explore HOMO-LUMO energies, determine energy band gaps for these substances, and predict reactive sites for their electrophilic, nucleophilic, and radical reactions. Significantly, ecotoxicity assessment, including ECOSAR predictions and acute toxicity tests, revealed that the PPs exhibited higher ecotoxicity to aquatic organisms than tiafenacil. Field experiments showed a half-life of 18.9 days for tiafenacil in water, fitting a first-order kinetic model (<i>R</i>² = 0.999), with a degradation of 41.5% after 14 days and approximately 89.2% after 60 days. This study significantly advances our understanding of tiafenacil's environmental fate, evaluates its associated risks, and offers valuable insights for its responsible application.