Application of two sample pretreatment methods in the determination of 111 residues of pesticides and related chemicals in aquatic products

Two sample pretreatment methods were developed and applied to determine 111 residues of pesticides in aquatic products. For Method I, the residues were extracted from homogenized tissue with acetone-ethyl acetate-n-hexane (1:1:1, v/v/v), and were then redissolved in acetonitrile; for Method II, the residues were extracted from homogenized tissue with acetonitrile-water under ultrasonication, and were then separated by liquid-liquid partition. The supernatants were purified using solid phase extraction (Envi-18 and PSA columns) prior to the GC-MS analysis. The determination was performed in selected ion monitoring (SIM) mode with external calibration for quantitative analysis. Under the optimal conditions, the detection limits (S/N = 3) for residues of pesticides were in the ranges of 0.001–0.026 mg/kg. The recoveries of Method I for the spiked standards at the concentration of 0.25 mg/kg were 72%–113% with the relative standard deviations (RSDs) of 3.4%–12.1%. The recoveries of Method II were 51%–127%, among which the recoveries for 94% pesticides were between 70% and 120%, with the RSDs of 3.2%–13.8%.