Determination of Residues of 6 Insecticides by Gas Chromagraphy-Tandem Mass Spectrometry Combined with QuEChERS Sample Preparation System

Pine forest soil samples were randomly collected, dried by air, removed impurities, ground and sieved. An aliquot (10 g) of the sample together with a zirconia ceramic bead bag (20 zirconia ceramic beads), 20 mL of acetonitrile and a QuEChERS extraction bag (containing 5.0 g of anhydrous magnesium sulfate and 1.0 g of sodium acetate) was taken and placed into the outer tube of the QuEChERS sample preparation system integration tube. A QuEChERS purification bag containing 1.0 g of anhydrous magnesium sulfate, 500 mg of PSA, 500 mg of C₁₈ and 15 mg of GCB was placed into the inner tube of the integration tube, and the integration tube was loaded into the QuEChERS sample preparation system. The mixture was shaken for 10 min and centrifuged for 5 min, and the above shaking and centrifugation processes were repeated once, to complete the extraction and purification of the sample. The purified solution was collected, and freeze centrifuged for 5 min. The supernatant was blown to near dryness at 50℃ by nitrogen, and the residue was dissolved by 1 mL of acetone. The resulting solution was passed through a 0.22 μm filter membrane, and the filtrate was analyzed by GC-MS/MS. Six insecticides (cyhalodiamide, fenvalerate, valerate, curmidophos, fensulfothion and fenitrothion) were separated by Rxi-5Sil MS column under temperature programmed conditions, ionized by EI source, detected by MRM mode, and quantified by external standard method. It was shown that linear relationships between values of the mass concentration and the peak area of the 6 insecticides were kept in the range of 0.01-3.00 mg·L^-1, with detection limits (3S/N) in the range of 0.012-0.021 μg·kg^-1. Test for recovery was made according to standard addition method, giving recoveries in the range of 86.2%-102%, and RSDs (n=5) of the determined values ranged from 1.6% to 4.2%. The proposed method was applied to the analysis of 5 actual samples, and fensulfothion, fenitrothion, fenvalerate and cyhalodiamide were detected, with detection amounts in the range of 14.22-125.35 μg·kg^-1.