Multiresidue determination of organophosphorus pesticides in corn oil using solid-phase extraction with lanthanum silicate sorbent and gas chromatography

Phosalone, malathion and diazinon were analyzed in corn oil using solid phase extraction (SPE)with lanthanum silicate as a new solid sorbent followed by gas chromatography with nitrogenphosphorus detection (GC-NPD). The efficiency of different eluents (methanol, dichloromethane,ethyl acetate, dichloromethane — ethyl acetate (1:1) and ethyl acetate — methanol (1:1)) werecompared for elution of organo-phosphorus pesticides on lanthanum silicate-SPE in corn oil.Recoveries with methanol as eluent were 87% for phosalone, 95% for malathion and 69% fordiazinon with standard deviations of 5-14% in the concentration range of 0.5-2 mg kg-1. Thelimits of detection for these organophosphorus pesticides, were lower than maximum residuelimits (MRLs) established by WHO/FAO. Thin layer chromatography was performed using bedof lanthanum silicate ion exchanger to ensure the existence of the pesticides residue in the SPEextract.They were determined using gas chromatograph equipped with nitrogen phosphorusdetector.