Banned in the U.S. and many other countries, Monocrotophos is a cheap and toxic organophosphate insecticide. It is especially toxic to birds, being blamed for widespread bird kills. Obelisc R was used to retain monocrotophos and separate it from impurities. Obelisc R contains embedded ionic and hydrophobic groups which can assist in fine tuning separations. Method is LC/MS compatible and can be used as a general approach for analyzing monocrotophos and other organophosphate insecticides.