Based on the acetonitrile-salt-H₂O aquatic two phase system, an effective sample pretreatment method was developed for the analysis of pyrethroids pesticides residues in fish by gas chromatography (GC). The fluorescence quenching method and GC were applied to study the form of pyrethroids pesticides in protein matrix of aquatic products. The influence factors on formation of acetonitrile-salt-H₂O system were discussed in depth. Meanwhile, the influence of the protein on extraction of pyrethroids pesticides from fish was detailedly investigated. The results showed that pyrethroids strongly bound with BSA by the hydrophobic interaction. In the φ(acetonitrile) 80%, a slow but full protein denaturation takes place, which causes the unfolding of protein and the release of pyrethroids. Then the drug residues was extracted into upper phase with high extraction efficiencies. Furthermore, the polarity of φ(acetonitrile) 80% is greater than φ (acetonitrile) 100%, the fat-soluble impurities are extracted less in φ(acetonitrile) 80% aqueous solution than that of in φ(acetonitrile) 100%. Therefore the purification steps were greatly simplified. The anhydrous magnesium sulfate (MgSO₄) and primary secondary amine (PSA) were added in upper phase to eliminate the moisture and other impurities. Then, the pyrethroids pesticides in extract (upper phase) was directly analyzed by GC. This method has been applied to the determination of pyrethroids pesticides residues in fish. The detection limits were in the range of 8～14 ng/mL, and the spiked recovery of fish were 81.1%～96.4%.

Key words: pyrethroids pesticides, aqueous two-phase system, protein, acetonitrile, gas chromatography