Rapid Determination of Residues of 96 Herbicides in Plant Derived Foods by Ultra-High Performance Liquid Chromatography-Quadrupole/Electrostatic Field Orbitrap High Resolution Mass Spectrometry

A method for the determination of residues of 96 common herbicides in plant derived foods was proposed by automatic QuEChERS combined with ultra-high performance liquid chromatography-quadrupole/electrostatic field orbitrap high resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS), meanwhile a mass spectral library for accurate mass numbers of 96 herbicides was established, which could enable qualitative screening of non-target compounds. 10.00 g of a high moisture sample (not less than 80% water content) or 5.00 g (2.00 g for the tea sample) of a low moisture sample (less than 15% water content) was taken, and 5 mL of water was added into a low moisture sample, settling for 30 min. 50 μL of 10 mg·L^-1 internal standard (±)-haloxyfop-d₄ solution, 5 beads of 4 mm zirconia, 10 mL of a mixture of acetonitrile solution containing 1% (volume fraction) acetic acid and toluene at a volume ratio of 9∶1 and buffer salt kit were sequentially added into the sample, and then the mixture were vortexed and centrifuged in QuEChERS automatic sample preparation system pre-loaded with adsorbent (containing 600 g of anhydrous magnesium sulfate, 100 mg of C₁₈, 100 mg of graphitized carbon black). 1 mL of the supernatant was taken and passed through 0.22 μm membrane, and the resulting solution was separated on Waters ACQUITY UPLC HSS-T3 column, using a mixture of methanol solution containing 5 mmol·L^-1 ammonium formate and 0.1%(volume fraction, the same below)formic acid-0.1% formic acid solution containing 5 mmol·L^-1 ammonium formate as the mobile phase in positive ion mode, and a mixture of methanol solution containing 5 mmol·L^-1 ammonium formate-5 mmol·L^-1 ammonium formate solution as the mobile phase in negative ion mode for gradient elution. Parallel reaction monitoring (PRM) scan mode in HRMS was used for qualitative screening and quantitative analysis with internal standard method. As shown by the results, linear ranges of the 96 herbicides were 5.0-100 μg·L^-1, with lower limits of determination low to 0.01 mg·kg^-1. Recovery test was carried out by the standard addition method on the blank samples with three matrices, kiwifruit, rice and tea, giving the results in the range of 72.9%-105%, with RSDs (n=6) of the determined values in the range of 2.1%-11%. The method was used for routine sampling of 90 different types of plant derived foods, of which 6 samples (matrices of rice, wheat and tea) contained herbicide residues.