Improved method for determination of chlorothalonil and related residues in cranberries.

Tetrachloroisophthalonitrile (chlorothalonil) was applied under controlled conditions in 1985 to a cranberry bog for fungus control and for residue studies. Randomly selected samples of cranberries were analyzed for residues of chlorothalonil, its metabolite 4-hydroxy-2,5,6-trichloroisophthalonitrile, hexachlorobenzene, and pentachlorobenzonitrile by extraction, methylation, Florisil column cleanup, and electron capture gas chromatography. Because of interferences in the GC determinative step, previously reported methodology was modified. The total residues found in the test samples were well below the permissible limit for the parent and related compounds.