Determination of Organophosphorus Pesticide Residues in Vegetable Oils by Single-Step Multicartridge Extraction and Cleanup and by Gas Chromatography

The method presented is applicable to the determination of organophosphorus (OP) pesticide residues in vegetable oils. The method performs in a single step an on-column extraction and cleanup of OP pesticide residues by means of a system of three cartridges. A solution of 1 g oil in n -hexane is loaded into an Extrelut-NT3 cartridge (large-pore diatomaceous material). The OP pesticide residues are extracted by eluting the cartridge with 20 mL acetonitrile, which is cleaned up by passing through a silica and a C18 cartridge connected on-line to the Extrelut NT-3 cartridge. A few milligrams of lipid is carried over into the eluate, which after concentration and solvent exchange is directly amenable to determination by gas chromatography (GC) with flame photometric detector with optical filter for phosphorus compounds (FPD-P). Recovery values for 45 OP pesticide residues are reported at two spiking levels. In the lower concentration range tested (0.09–0.60 mg/kg), satisfactory results (74–86%) were obtained for 39 OP pesticides; exceptions were formothion (5%), disulfoton (32%), phosalone (54%), demeton-S -methyl sulfone (60%), fenthion (62%), and borderline phosphamidone (68%). In the higher concentration range tested (0.38–2.35 mg/kg), satisfactory results (82–109%) were obtained for 43 OP pesticides; exceptions were formothion (48%) and disulfoton (53%). Compared to conventional techniques, such as liquid-liquid partition and size-exclusion chromatography (SEC), the method described is faster and simpler, requires minimal solvents and essentially only disposable items, and does not require skilled operators or maintenance of costly apparatus.