Modification of the AOAC method for determination of fumigants in wheat.

The official first action AOAC method for determination of residues of fumigants in grains has been modified for use by 6 laboratories in an FDA pesticide surveillance program. A 15% OV-17 gas-liquid chromatographic column, installed in a chromatograph equipped with a constant current 63Ni electron capture detector, provides for improved resolution, multiresidue capability, and lower limits of detection. A study was made of the behavior of chloroform, carbon tetrachloride, ethylene dichloride, trichloroethylene, tetrachloroethylene, and ethylene dibromide through the method. Recoveries from fortified wheat samples averaged 105-115%. Experimental evidence is presented which suggests that part of the consistent trend toward high recovery can be attributed to selective sorption of acetone by the CaCl2 used in the final drying step.