Purge and Trap Method for Determination of Fumigants in Whole Grains, Milled Grain Products, and Intermediate Grain-Based Foods

Abstract

A method developed for the determination of 1,2-dibromoethane in whole grains and grain-based products has been modified and expanded to include 8 other fumigants. Samples are stirred with water and purged with nitrogen for 0.5 h in a water bath at 100 degrees C. The fumigants are collected on a trap composed of Tenax TA and XAD-4 resin, eluted with hexane, and determined by gas chromatography (GC) using electron capture detection or Hall electrolytic conductivity detection. Flame photometric detection in the sulfur mode is used to determine carbon disulfide. Thick-film, wide-bore capillary columns were used exclusively in both the determination and confirmation of the halogenated fumigants. The higher levels of fumigants are also confirmed by full scan GC/mass spectrometry. Samples are analyzed for carbon disulfide, methylene chloride, chloroform, 1,2-dichloroethane, methyl chloroform, carbon tetrachloride, trichloroethylene, 1,2-dibromoethane, and tetrachloroethylene. A total of 25 whole grains, milled grain products, and intermediate grain-based foods analyzed by this method contained fumigant levels up to 51 ppm (carbon tetrachloride in wheat). Recoveries from fortified samples ranged from 82 to 104%. Chromatograms from this purge and trap method are clean, so that low parts per billion and sub-parts per billion levels can be quantitated for the halogenated analytes. The quantitation level for carbon disulfide is 12 ppb.