METHOD FOR THE DETERMINATION OF ORGANOPHOSPHORUS PESTICIDE RESIDUES IN OKRA (ABLEMOSCHUS ESCULENTUS) BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

A method basing on liquid chromatography-mass spectrometry (LC-MS/MS) was developed for sensitive determination of Organophosphorus pesticides namely Monochrotophos, Quinalphos and Chlorpyrifos in okra in Andhra Pradesh (South India). The method involves extraction of 10 g of homogenized okra samples (2 g of Sodium chloride + 8 g of Magnesium sulfate) with 10 mL of acetonitrile later cleaned up by dispersive solid phase extraction with the combination of primary secondary amine (PSA), graphitized carbon black (GCB), C18, and anhydrous magnesium sulfate. Final analysis was performed by liquid chromatography-dear() spray ionization-tandem mass spectrometry operated in the multiple reaction monitoring (MRM) mode, acquiring two specific precursor-production transitions per target compound. The average recoveries measured at 10 mu g/kg were in the range 81-106% for all of the compounds tested with relative standard deviations below 14%. The methodology has been proven to be highly efficient and robust and thus the method is highly suitable for monitoring the Maximum Residue Limits (MRL) compliance of the pesticides.