Simultaneous determination of 76 pesticide residues in the traditional Chinese medicine by magnetic hydrophilic-lipophilic-balanced materials assisted matrix solid phase dispersion extraction-high performance liquid chromatography-tandem mass spectrometry

Traditional Chinese medicine (TCM) is gaining popularity worldwide, but its quality is often affected by excessive pesticide residues during cultivation and production. A sensitive and reliable method for the simultaneous determination of multi-residue pesticides in TCMs is the key to guarantee the quality and safety of TCMs. In this study, broad-spectrum hydrophilic-lipophilic balanced magnetic adsorbents were prepared for the magnetic matrix solid phase dispersion (MMSPD) extraction of 76 pesticides from three different TCMs before their detection by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Unlike the traditional matrix solid phase dispersion (MSPD), which required tedious SPE column packing, an external magnetic field was employed in our method for magnetic isolation and extraction from TCM samples, followed by grounding adsorption. First, broad-spectrum hydrophilic-lipophilic balanced magnetic adsorbents, Fe3O4@PLS, were successfully fabricated by the swelling polymerization of divinyl benzene (DVB) and N-vinyl pyrrolidone (NVP) on the surface of Fe3O4 magnetic particles. The prepared materials were systematically characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffractometry (XRD) for their morphologies, chemical structure, and crystalline structure. Then, the obtained magnetic particles (Fe3O4@PLS) were applied to MMSPD for the simultaneous extraction and analysis of the 76 pesticides in honeysuckle, chrysanthemum, and pseudo-ginseng root (dry) prior to detection by HPLC-MS/MS. In order to establish the optimal extraction conditions, the key parameters affecting the MMSPD extraction efficiency were optimized, including the amount of magnetic materials Fe3O4@PLS (5, 10, 12, 15, 20 mg), volume fractions of methanol in water for matrix purification (0%, 5%, 10%, 20%, 25%), grinding adsorption time for dispersion (2, 3, 4, 5, 6 min), type (methanol, methanol containing 0.1% (v/v) formic acid, acetonitrile, acetonitrile containing 0.1% (v/v) formic acid) and volume (0.5, 1, 2, 2.5, 5 mL) of elution solvent, and vortex time for desorption (1, 2, 3, 4, 5 min). Finally, the optimal conditions were set as follows: 10 mg of the magnetic adsorbent Fe3O4@PLS, 10 mL 20% (v/v) of methanol in water with a vortex time of 1 min for matrix purification, grinding time of 5 min for dispersion and adsorption, 0.5 mL acetonitrile containing 0.1% (v/v) formic acid as the elution solvent, and vortex time of 1 min for desorption. Then, the 76 pesticides were separated on an Agilent ZORBAX Eclipse Plus C18 column (100 mm×3.0 mm, 1.8 μm) with gradient elution and analyzed in multiple reaction monitoring (MRM) mode by positive electrospray ionization (ESI+). Under the optimal conditions, good linearities were obtained for the 76 pesticides in the concentration ranges of 10 to 200 μg/kg, with correlation coefficients (r2)≥0.9965. The limits of detection (LODs, S/N=3) were in the range of 0.6-3.0 μg/kg, and the limits of quantification (LOQs, S/N=10) ranged from 2.0 to 10.0 μg/kg. The proposed method was successfully applied to 76 pesticide residue analysis in honeysuckle, chrysanthemum, and pseudo-ginseng root (dry). At three spiked levels, the recoveries were 69.1%-112.2%, 67.1%-102.8% and 70.1%-105.1%, with RSDs of 2.0%-12.4%, 2.1%-13.2% and 2.0%-13.5% for honeysuckle, chrysanthemum, and pseudo-ginseng root(dry), respectively. The prepared magnetic material Fe3O4@PLS has the characteristics of both strong magnetic responsibility and high broad-spectrum adsorption property for hydrophilic (e. g., carbendazim) and lipophilic (e. g., edifenphos) pesticides. The implementation of the MMSPD method before the analysis of the 76 pesticides by HPLC-MS/MS has the following advantages: less consumption of the magnetic materials, sample, and organic solvent; simple operation; high sensitivity; and satisfactory accuracy and precision. Hence, this is a potential method for the simultaneous determination of multiple pesticide residues in complex non-liquid TCM samples.