Abstract:

Based on ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UPLC-QTOF-MS), UNIFI 1.7.0 software was used to establish a screening and confirmation method for the analysis of 91 pesticide residues, which was qualitatively validated and applied to tea screening in the circulation market. By analyzing the collected pesticide certified reference materials (CRM), a mass spectral database of 91 pesticides was constructed. The database contains multiple types of information, including formulas, theoretical exact masses, retention times, characteristic fragment ions, and adduct types. The samples were extracted with acetonitrile, purified on a solid-phase extraction column, and separated on an Acquity BEH C18 column. All the data (ESI+) were acquired in MS^E mode and analyzed using the UNIFI information system. Analyte detection was based on the retention time deviation ±0.1 min, accurate mass deviation ±5×10^-6, and major adduct forms including [M+H]⁺, [M+Na]⁺, [M+K]⁺, and [M+NH₄]⁺. Screening was performed by the software in an automated fashion. Compound identification was accomplished with retention time matching and accurate mass measurements of the primary diagnostic ions for each analyte. To ensure accuracy of the identification results, information from the MS/MS profiles must be compared with online mass spectral libraries such as PubChem and MassBank. The SANTE/11813/2017 protocol for the validation of the screening method was followed. A mixed standard solution was spiked to 21 tea samples at four levels (0.01 mg/kg, 0.05 mg/kg, 0.10 mg/kg, and 0.20 mg/kg) to determine the screening detection limit (SDL) of each pesticide, and a total of 1911 pesticide/sample combinations were evaluated. The results revealed 66 pesticides with an SDL of 0.01 mg/kg, eight pesticides with an SDL of 0.05 mg/kg, one pesticide with an SDL of 0.10 mg/kg, three pesticides with an SDL of 0.20 mg/kg, and 13 pesticides with an SDL greater than 0.20 mg/kg. One pesticide showed matrix-inhibitory effects in the screening tests. Finally, the established method was used to analyze the pesticide residues in 22 tea samples available on the market. Six pesticide compounds were found in the tea samples, all of which were confirmed to be positive after artificial identification. This method provides a reference for the high-throughput screening and detection of pesticide residues in tea as well as a research approach for the analysis of various chemical contaminants in other matrices.

Key words: ultra-performance liquid chromatography (UPLC), quadrupole-time-of-flight mass spectrometry (QTOF-MS), pesticide residues, tea, screening and confirmation, database, qualitative method validation