Cypermethrin residues determination in the milk of a lactating dairy cow by gas chromatography-ion trap mass spectrometry.

The aim of this work was to detect and quantitate residues of the pyrethroid insecticide cypermethrin in the milk of a lactating dairy cow. The efficiency of the method was settled through recovery experiments in which certain amounts of the pyrethroid cypermethrin were spiked up to milk. For this purpose, the matrix solid-phase dispersion method was applied followed by clean-up with silica-gel column. The extracts obtained were analyzed by gas chromatography-ion trap mass spectrometry. With the aid of the selected ion storage technique, it was feasible to select specific ions from the analyte of interest, which could be separated from the organic matrix. After the establishment of optimum conditions for the detection of pyrethroid residues of cypermethrin, samples of milk were collected from a cow submitted to a veterinary treatment for elimination of parasites using an insecticide with 50 g/L of active ingredient in its formula. The data obtained showed milk contamination with a maximum concentration of 0.168 mg/kg 24 h after insecticide treatment. Considering the maximum residual limit for cypermethrin in milk of 0.010 mg/kg, samples collected 15 and 24 h after treatment showed concentrations about 16 times above this value, and samples collected 11 days after treatment showed concentrations about 7 times above this value. Seventeen days after treatment, cypermethrin was not detected in the milk.