Development of a headspace solid-phase microextraction/gas chromatography-mass spectrometry method for determination of organophosphorus pesticide residues in cow milk

In the past few years, organophosphorus compounds become one of the most widely used classes of pesticides due to their acute toxicity against a wide variety of pests. In this work, a method based on solid-phase microextraction in mode headspace (HS-SPME) coupled to gas chromatography-mass spectrometry (GC-MS) was developed and optimized through multivariate factorial design to determine residues of organophosphorus pesticides in cow's milk. Different parameters of the method were evaluated, such as fiber type, temperature, extraction and desorption times, sample volume, effect of salt addition and stirring velocities. The evaluated pesticides were dichlorvos, sulfotep, demeton-S, dimpylate, disulfoton, parathion, methyl parathion, fenitrothion, chlorpyrifos and ethion. The best results were obtained using polydimethylsiloxane/divinylbenzene fiber and headspace mode at 90 °C for 45 min, along with stirring at 600 rpm and desorption for 5 min at 250 °C. Under the optimized conditions, the proposed methodology was able to determine all of the pesticides with variation coefficients between 6.1% and 29.5%. Detection and quantification limits ranged from 2.16 to 10.85 μg L− 1 and from 6.5 to 32.9 μg L− 1, respectively. To evaluate residues of these pesticides in milk, cows were exposed to the pesticides of interest and milk was collected after 24 h. The developed method was able to detect trace amounts of these pesticides in the collected milk samples.