Simultaneous Determination of Residues of 46 Pesticides in Lycium Ruthenicum Murr. by Ultra-High Performance Liquid Chromatography-Tandem Mass Spectrometry after QuEChERS Purification

A method for the simultaneous determination of residues of 46 pesticides in Lycium ruthenicum Murr. by ultra-high performance liquid chromatography-tandem mass spectrometry after QuEChERS purification was proposed. Lycium ruthenicum Murr. sample was freeze-dried, crushed and sieved. An aliquot (5.00 g) was taken, and 15 μL of 100 μg·L^-1 internal standard solution and 5 mL of water were added. The mixture was swirled well, soaked for 10 min, and extracted with 10 mL of acetonitrile solution containing 1% (volume fraction) acetic acid, and 4.0 g of anhydrous magnesium sulfate and 1.0 g of sodium chloride were added. After shake, vibration and centrifugation, the supernatant was transferred to the centrifuge tube preloaded with 1.0 g of anhydrous magnesium sulfate. After vibration and centrifugation again, 2 mL of the supernatant was added into the centrifuge tube containing 20 mg of N-propyl ethylene diamineethy, 20 mg of octadecylsilane bonded silica gel and 25 mg of graphitized carbon black. After vibration and centrifugation, the supernatant was taken for determination. Eclipse Plus C₁₈ column was used as the stationary phase, and 0.1% (volume fraction) formic acid solution containing 10 mmol·L^-1 ammonium formate-acetonitrile were used as the mobile phase system for gradient elution. The separated targets were detected by triple quadrupole mass spectrometry detector with drying temperature of 350℃ and sheath temperature of 300℃. Standard curves were drawn with the matrix matching mixed standard solutions, and internal standard method was used for quantification. It was shown that the matrix effect values of 46 pesticides in the sample purified by QuEChERS ranged from -48.4% to 39.5%, and the linear ranges of working curves of 46 pesticides were 6.0-600.0 μg·kg^-1, with detection limits in the range of 0.2-4.2 μg·kg^-1. Test for recovery was made on the blank samples by standard addition method, giving results in the range of 47.5%-129%, and RSDs (n=6) of the determined values were in the range of 3.0%-17%. This method was applied to analysis of 12 batches of Lycium ruthenicum Murr. samples. Thirteen pesticides were detected in 6 batches of Lycium ruthenicum Murr. samples, and the other pesticides were not detected. According to GB 2763-2021, the detection amounts of 12 pesticides met the requirements, but the detection amount of carbofuran(22.9±2.3)μg·kg^-1 in 1 batch of sample did not meet the requirements for residue limits (20 μg·kg^-1).