Modified Storherr method for determination of organophosphorus pesticides in nonfatty food Total Diet composites

The method for Storherr et al. for organophosphorus pesticide residues in nonfatty foods has been modified to permit its use in analyzing the composites of nonfatty foods in the Food and Drug Administration Total Diet Program. Modifications were designed to permit the examination by gas-liquid chromatography (GLC) of the larger weight (100 mg) of sample equivalent required by the Total Diet Program. To achieve a limit of quantitation of 2 ppb parathion, the organophosphorus pesticides are determined by GLC equipped with flame photometric detector (P-mode) and/or KCL thermionic detector. Recovery data, ranging from 70 to 133%, are presented for fortification (2-10 ppb) of organophosphorus pesticides in 7 nonfatty food Total Diet composites. The modified Storherr method was successfully tested in an intralaboratory method trial of 2 Total Diet composites (potatoes and legumes) fortified at 5-13 ppb with malathion, parathion, paraoxon, and monocrotophos. In addition, the modified Storherr method was compared to existing FDA Total Diet methodology for the determination of incurred organophosphorus residues. Residue levels found by both methods were similar for malathion (30 ppb), parathion (7 ppb), and diazinon (1 ppb), but only the modified Storherr method was capable of determining about 10 ppb dimethoate and phorate in the cereals and grains composite.