Diazinon is a nonsystemic organophosphate insecticide developed in the early 1950’s. It was heavily used as an all-purpose indoor/outdoor home pesticide, but was banned for home use in 2004. The thiophosphoric ester in diazinon can form toxic phosphine gases and phophorus oxides. The EURL (European Union Reference Laboratory), included diazinon as a target pesticide for the EUPT-CF9 a proficiency test for cereals and feedingstuff that require muli-residue methods. Primesep B2 and Obelisc R were used to retain carbofuran and separate it from impurities. Primesep B2 contains embedded basic ion-pairing groups and 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 diazinon, other organophosphate insecticides, and dozens of other pesticides.