Gas-liquid chromatographic determination of sodium 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate residues on soybeans and foliage, soil, milk, and liver.

Residues of sodium 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate and its free acid are determined by treating a sample extract with diazomethane to convert the residues to methyl 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate. This compound is purified by chromatography on Florisil and measured by electron capture gas-liquid chromatography. The method has been used on soybeans, soybean foliage, soil, milk, and liver. It can detect 0.01 ppm with recoveries of 70--75%.