Preparation and stability of dilute insecticide analytical standards for gas chromatography

Abstract

A convenient and economical procedure for preparing and storing accurately measured amounts (1.00 mg) of insecticide analytical standards is described. The validity of the method was evaluated in a 2-year study of the storage stability of carbofuran, chlorfenvinphos, diazinon, dichlorvos (DDVP), stability of carbofuran, chlorfenvinphos, diazinon, dichlorvos, disulfoton and disulfoton sulphone. Solutions (1 mg ml^–1) of each insecticide were prepared in hexane, toluene or acetone and aliquots sealed in glass ampoules were stored at –20, 1 and 20 °C. After 0.25, 0.5, 1.0 and 2.0 years the mean concentrations of all compounds, except dichlorvos, were within 0.9% of fresh solutions of the original standards; dichlovos was 3.6% greater. Neither the type of solvent nor the storage temperature had significant (P= 0.05) effects on the concentrations but there were large differences in purity between different batches of primary standards of all the organophosphorus insecticides.